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Prospects of Gasoline Compression Ignition (GCI) Engine Technology in Transport Sector
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Abstract
Compression ignition (CI) engines are mainly fuelled by diesel-like high cetane fuels, and they have higher overall efficiency due to higher compression ratio compared to their spark ignition (SI) engine counterparts. However, modern diesel engines are more expensive, complicated, and emit high nitrogen oxides (NOx) and particulate matter (PM). Simultaneous control of soot and NOx emissions in diesel engines is quite challenging and expensive. Thermal efficiency of SI engines, on the other hand is limited by the tendency of abnormal combustion at higher compression ratios therefore use of high octane fuel is essential for developing more efficient higher compression ratio SI engines in near future. In the foreseeable future, refineries will process heavier crude oil to produce relatively inferior petroleum products to power the IC engines. Also, fuel demand will shift more towards diesel and jet fuels, which would lead to availability of surplus amounts of low octane gasoline with oil marketing companies, with little apparent use for operating the engines. This low octane gasoline will be cheaper and would be available in excess quantities in foreseeable future as the demand for gasoline will further drop due to increase in the fuel economy of modern generation gasoline fuelled vehicles. For addressing these issues, Gasoline compression ignition (GCI) engine technology is being developed, which is a futuristic engine technology that takes advantage of higher volatility, and higher auto-ignition temperature of gasoline and higher compression ratio (CR) of a diesel engine simultaneously to take care of soot and NOx emissions without compromising diesel engine like efficiency. GCI engines can efficiently operate on low octane gasoline (RON of ~70) with better controls at part load conditions. However cold starting, high CO and HC emissions, combustion stability at part load, and high combustion noise at medium-to-full load operations are some of the challenges associated with GCI engine technology. Introductory sections of this chapter highlights future energy and transport scenario, trends of future fuel demand, availability of low octane fuels and development in advanced engine combustion technologies such as HCCI, PCCI, RCCI, and GDI. GCI engine development, its combustion characteristics and controls are discussed in detail. Particular emphasis is given to the effect of various control strategies on GCI combustion, performance and emissions, fuel
quality requirement and adaption of GCI technology in modern CI engines. In addition, this chapter reviews initial experimental studies to assess the potential benefits
of GCI technology.
... The intensity and duration of the hottest part of the flame during combustion affect the amount of NOx (Akal et al., 2020;Cho & He, 2007;Thiyagarajan et al., 2022). Due to the heat generated during compression, diesel fuel spontaneously ignites in the engine because the amount of air in the cylinder of a diesel engine is roughly twice that of a petrol engine (Solanki et al., 2020). Remarkably, the findings show that CO emissions from diesel engines are lower than NOx emissions. ...
The study delves into how vehicle engine characteristics impact the release of air pollutants from various vehicle fleets in Lagos, Nigeria. It involved the direct measurement of emissions from the exhaust pipes of 88 vehicles using gas analyzers. The vehicle fleet encompassed motorcycles, tricycles, private cars, minibuses, large buses, and trucks. A statistical analysis was conducted on carbon monoxide (CO) and nitrogen oxide (NOx) emissions to develop a model equation based on vehicle type, engine type, vehicle age, and purchase status. Results indicate that personal cars and minibuses predominantly emit CO from gasoline engines, whereas large buses and trucks significantly contribute to NOx emissions from diesel engines. Further scrutiny revealed that 66% of the vehicles examined were over 10 years old, resulting in a 65% increase in emission levels. Approximately 60% of gasoline and 75% of diesel vehicles exceeded the permissible emission limits, leading to air quality deterioration and heightened health risks. The study underscores the risks associated with ageing vehicles and different engine types, emphasizing the imperative for a gradual transition to low-carbon or electric vehicles in developing African cities to combat air pollution and mitigate health hazards. ARTICLE HISTORY
... A GCI engine benefits from the higher auto-ignition temperature and higher compression ratios of diesel engines [9]. In the GCI concept, gasoline-like fuels, which are difficult to ignite compared to diesel fuels, are injected using different injection strategies to achieve partially premixed combustion. ...
Internal combustion (IC) engines play an important role in the global economy by powering various transport applications. However, it is a leading cause of urban air pollution; therefore, new combustion strategies are being developed to control emissions. One promising advanced low-temperature combustion (LTC) technology is gasoline compression ignition (GCI). This experimental study assesses the performance of a two-cylinder engine, emissions, and exhaust particulate characteristics using G80 (80% v/v gasoline and 20% v/v diesel) blend operating in GCI mode vis-à-vis baseline conventional diesel combustion (CDC) mode using diesel. The effects of double pilot injection, Pilot-1 proportion (10-30%), and main injection timing were investigated on the GCI combustion. Experiments were performed at different engine loads (3, 4, and 5 bar brake mean effective pressure [BMEP]) at a constant engine speed (2000 rpm). GCI combustion showed higher brake thermal efficiency (BTE) than CDC mode at medium loads. Hydrocarbon (HC) and carbon monoxide (CO) emissions increased in GCI mode, but oxides of nitrogen (NOx) were reduced than the baseline CDC mode. High pilot ratio and late main injection timing tests showed higher HC and CO emissions in the GCI mode at low engine loads. The GCI mode engine emitted higher nucleation mode particles and nanoparticles than baseline CDC mode at high engine loads. Using a triple injection strategy, GCI engines simultaneously reduced NOx and particulate matter (PM) emissions, especially at high loads. Controlling these emissions in baseline CDC mode engines is otherwise quite challenging.
... The GCI combustion mode is an advanced low-temperature combustion (LTC) technique. LTC techniques take advantage of the high autoignition of SI engines and the high compression ratio of CI engines (Solanki et al., 2020;Wei et al., 2020), resulting in low soot and NOx emission in exhaust gas while maintaining high efficiency. GCI engines operate on fully premixed homogeneous combustion (e.g., homogeneous charge compression ignition [HCCI]), partially premixed combustion (PPC; G. Kalghatgi et al., 2010;Rezaei et al., 2013;Sellnau et al., 2014), and diffusion-controlled combustion modes under low, medium, and high load conditions, respectively. ...
In this study, conventional gasoline with a RON of 95 and gasoline–ethanol blend (20% ethanol in volume [E20]) were experimentally compared in terms of combustion characteristics and performance. First, second injection timing (SOI2) was investigated to study combustion characteristics while maintaining the dilution level at 25%. In this part, two fuels with high octane numbers were used to investigate the influence of ethanol on combustion characteristics under gasoline compression ignition (GCI) mode. The in-cylinder pressure and heat-release rate (HRR) indicated that the fueling of the engine with E20 leads to the maximum peak pressure and easier position of maximum HRR in comparison with pure gasoline in all cases of the second injection. The main HRR curve of E20 moves closer to the top dead center (TDC) compared with that of gasoline. This HRR behavior indicates that the overall HRR of E20 is more compact than that of gasoline. Second, SOI2 was fixed at two cases of −6, −3 crank angle degree (CAD) after TDC (ATDC), charge dilution and boosted pressure were investigated to study the sensitivity of dilution on combustion characteristics with gasoline–ethanol blend fuel. The in-cylinder pressure and HRR indicated a two-stage combustion phenomenon for a low dilution ratio (from 0% to 15%) and a single stage with a peak at approximately 5–6 CAD ATDC at high dilution.
div class="section abstract"> The combustion instability at low loads is one of the key technology risks that needs to be addressed with the development of gasoline compression ignition (GCI) engine. The misfires and partial burns due to combustion instability leads to excessive hydrocarbon (HC) and carbon monoxide (CO) emissions. This study aims to improve the combustion robustness and reduce the emissions at low loads. The GCI engine used in this study has unique hardware features of a spark plug placed adjacent to the centrally mounted gasoline direct injector and a shallow pent roof combustion chamber coupled with a bowl in piston geometry. The engine experiments were performed in a single cylinder GCI engine at 3 bar indicated mean effective pressure (IMEP) and 1500 rpm for certified gasoline with research octane number (RON) = 91. Enabling strategies such as internal exhaust gas recirculation (i-EGR), compression ratio (CR = 16 & 18) and spark assisted ignition were investigated to improve the combustion robustness. Several other control variables such as intake temperature, intake pressure, fuel injection pressure, fuel injection timing, and exhaust back pressure were used to optimize the operation under low load conditions.
The experimental study revealed that exhaust rebreathing supports the combustion stability but with the difficulty of precise back pressure control. For CR = 16 piston, exhaust re-breathing (i-EGR) combined with spark assistance enables to achieve a coefficient of variation (COV) below 2% with NO<sub>X</sub> emission of around 0.1 g/kWh. At higher CR = 18, pressure and temperature conditions are favorable to support the auto-ignition driven combustion without exhaust rebreathing. For improved combustion stability, spark assistance is needed with CR = 18 piston. Optimum spark shortened the burn rate, improved the combustion stability, and reduced the HC emissions. The effects of the flame initiated by the spark plug on the overall combustion is limited to the vicinity of spark arc. Overall, when fuel mixture is stratified under partially premixed compression ignition (PPCI) conditions, spark is needed to strengthen the ignition behavior without disturbing the major auto-ignition combustion behavior.
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Various low-temperature combustion strategies (namely, homogeneous charge compression ignition, reactivity controlled compression ignition, and partially premixed charge compression ignition) have shown the potential to comply with upcoming and prevailing stringent emissions legislations. Low octane gasoline has emerged as an ideal fuel candidate for premixed charge combustion under diesel-like conditions in gasoline compression ignition (GCI) engines. GCI is an excellent technology to rectify future global energy demand imbalance, because it aims to replace diesel (which is in short supply) with low octane fractions/naphtha (which is in surplus supply) in compression ignition engines. However, this novel combustion concept requires modifications in the conventional design of diesel engines. The combustion chamber shape and in-cylinder flows play a crucial role in charge distribution and temperature stratification. Therefore, understanding the combined effect of combustion chamber geometry and in-cylinder flows is essential for future engine designs. GCI combustion engine simulations for varying swirl ratios (SRs) were performed in CONVERGE CFD software to understand the effect of in-cylinder air motion on the mixture stratification and combustion. A 1/7th sector geometry for a conventional re-entry piston bowl was modeled and then simulated. Two different mechanisms were used for model validation. The results indicated that the large-scale flow structures govern the fuel distribution in the combustion chamber. The charge convection because of increased swirl has a substantial effect on the combustion characteristics of the engine. A distinguished ignition kernel was observed for all test cases. An interfacial region with counter-rotating vortices formed a lean mixture zone, hindering flame propagation and combustion. A lower SR, shallow depth piston, and modifications to avoid flame quenching in the squish zone need to be further investigated to optimize the engine performance.
Transport is almost entirely powered by internal combustion engines (ICEs) burning petroleum-derived liquid fuels and the global demand for transport energy is large and is increasing. Available battery capacity will have to increase by several hundred fold for even light duty vehicles (LDVs), which account for less than half of the global transport energy demand, to be run on electricity alone. However the greenhouse gas (GHG) impact of battery electric vehicles (BEVs) would be worse than that of conventional vehicles if electricity generation and the energy used for battery production are not sufficiently decarbonized. If coal continues to be a part of the energy mix, as it will in China and India, and if power generation is near urban centers, even local urban air quality in terms of particulates, nitrogen oxides and sulfur dioxide would get worse. The human toxicity impacts associated with the mining of metals needed for batteries are very serious and will have to be addressed. Large prior investments in charging infrastructure and electricity generation will be needed for widespread forced adoption of BEVs to occur. There will be additional costs in the short term associated with various subsidies required to promote such a change and in the longer term, the loss of revenue from fuel taxes which contribute significantly to public finances in most countries. ICEs will continue to power transport, particularly commercial transport, to a large extent for decades to come and will continue to improve. There will also be a role for low-carbon and other alternative fuels where they make sense. However such alternatives also start from a low base and face constraints on rapid and unlimited growth so that they are unlikely to make up much more than 10% of the total transport energy demand by 2040. As the energy system is decarbonized and battery technology improves there will be an increasing role for BEVs and hydrogen which could replace liquid hydrocarbons in transport and the required infrastructure will evolve. Meanwhile, there will certainly be increasing electrification, particularly of LDVs in the form of hybridization to improve ICEs.
The worldwide demand for transport fuels will increase significantly but will still be met substantially (a share of around 90%) from petroleum-based fuels. This increase in demand will be significantly skewed towards commercial vehicles and hence towards diesel and jet fuels, leading to a probable surplus of lighter low-octane fuels. Current diesel engines are efficient but expensive and complicated because they try to reduce the nitrogen oxide and soot emissions simultaneously while using conventional diesel fuels which ignite very easily. Gasoline compression ignition engines can be run on gasoline-like fuels with a long ignition delay to make low-nitrogen-oxide low-soot combustion very much easier. Moreover, the research octane number of the optimum fuel for gasoline compression ignition engines is likely to be around 70 and hence the surplus low-octane components could be used without much further processing. Also, the final boiling point can be higher than those of current gasolines. The potential advantages of gasoline compression ignition engines are as follows. First, the engine is at least as efficient and clean as current diesel engines but is less complicated and hence could be cheaper (lower injection pressure and after-treatment focus on control of carbon monoxide and hydrocarbon emissions rather than on soot and nitrogen oxide emissions). Second, the optimum fuel requires less processing and hence would be easier to make in comparison with current gasoline or diesel fuel and will have a lower greenhouse-gas footprint. Third, it provides a path to mitigate the global demand imbalance between heavier fuels and lighter fuels that is otherwise projected and improve the sustainability of refineries. The concept has been well demonstrated in research engines but development work is needed to make it feasible on practical vehicles, e.g. on cold start, adequate control of exhaust carbon monoxide and hydrocarbons and control of noise at medium to high loads. Initially, gasoline compression ignition engines technology has to work with current market fuels but, in the longer term, new and simpler fuels need to be supplied to make the transport sector more sustainable.
Gasoline Compression Ignition (GCI) engines based on Gasoline Partially Premixed Combustion (GPPC) showed potential for high efficiency and reduced emissions of NOx and Soot. However, because of the high octane number of gasoline, misfire and unstable combustion dramatically limit low load operating conditions. In previous work, seeding the intake of the engine with ozone showed potential for increasing the fuel reactivity of gasoline. The objective of this work was to evaluate the potential of ozone to overcome the low load limitations of a GCI engine. Experiments were performed in a single-cylinder light-duty CI engine fueled with 95 RON gasoline. Engine speed was set to 1500 rpm and intake pressure was set to 1 bar in order to investigate typical low load operating conditions. In the first part of the work, the effect of ozone on gasoline autoignition was investigate while the start of the fuel injection varied between 60 CAD and 24 CAD before TDC. Results showed that earlier injection timings improved the promoting effect of ozone on gasoline autoignition mainly because of the extension of the fuel-ozone residence time. Moreover, results showed how the nitrogen monoxide (NO) contained in the residual burn gases can react with O 3 molecules before they can decompose releasing the O responsible for the autoignition enhancement. In the second part of the work, results showed that seeding the intake of the engine with of 383 ppm of ozone, allowed to improve the gasoline reactivity and to reduce the intake temperature from 130°C to 40°C at a constant IMEP of 3 bar. Analysis showed that while ozone is employed to reduce the intake temperature, combustion initiated and developed at lower temperature with advantages in term of NOx emissions. Also unburned hydrocarbon HC emission reduced, while CO emission increased. In order to take advantage of the effect of ozone, the injection strategy had to be adapted: a first injection during the intake stroke was necessary to get the promoting effect of ozone while a second injection during compression stroke was employed to induce the fuel stratification necessary for controlling the combustion phasing and to avoid excessive heat release rate.
Most of the researchers wanted to work with diesel engine because of complexity in the gasoline engine. Author tried to review gasoline direct injection (GDI) a new technology in the gasoline engine with the objective to motivate the researchers to work with this field. This paper reviews the benefits of direct injection in the gasoline engine in terms of fuel consumption and emission. The effect of stratified and homogeneous mode on the performance parameter along with combustion system (wall guided/ spray guided and air guided), its extend feasibility and complexity in the individual and combine mode of operation is reviewed in detail. The review comes up with the need of optimization in mixture formation to reduce in-cylinder wall wetting, increase combustion stability, and extend up to which charge cooling occurs and feasibility of stratified mode operation in GDI engine. Optical diagnostic and CFD are the tools which can help in optimizing this complex system
As demand evolves, as specifications change, and as new fuel opportunities arise, what are the implications for refiners up to mid-century?
Many research studies have shown that low temperature combustion in compression ignition engines has the ability to yield ultra-low NOx and soot emissions while maintaining high thermal efficiency. To achieve low temperature combustion, sufficient mixing time between the fuel and air in a globally dilute environment is required, thereby avoiding fuel-rich regions and reducing peak combustion temperatures, which significantly reduces soot and NOx formation, respectively. It has been demonstrated that achieving low temperature combustion with diesel fuel over a wide range of conditions is difficult because of its properties, namely, low volatility and high chemical reactivity. On the contrary, gasoline has a high volatility and low chemical reactivity, meaning it is easier to achieve the amount of premixing time required prior to autoignition to achieve low temperature combustion. In order to achieve low temperature combustion while meeting other constraints, such as low pressure rise rates and maintaining control over the timing of combustion, in-cylinder fuel stratification has been widely investigated for gasoline low temperature combustion engines. The level of fuel stratification is, in reality, a continuum ranging from fully premixed (i.e. homogeneous charge of fuel and air) to heavily stratified, heterogeneous operation, such as diesel combustion. However, to illustrate the impact of fuel stratification on gasoline compression ignition, the authors have identified three representative operating strategies: partial, moderate, and heavy fuel stratification. Thus, this article provides an overview and perspective of the current research efforts to develop engine operating strategies for achieving gasoline low temperature combustion in a compression ignition engine via fuel stratification. In this study, computational fluid dynamics modeling of the in-cylinder processes during the closed valve portion of the cycle was used to illustrate the opportunities and challenges associated with the various fuel stratification levels.
Premixed Charge Compression Ignition (PCCI), a Low Temperature Combustion (LTC) strategy for diesel engines is of increasing interest due to its potential to simultaneously reduce soot and NO x emissions. However, the influence of mixture preparation on combustion phasing and heat release rate in LTC is not fully understood. In the present study, the influence of injection timing on mixture preparation, combustion and emissions in PCCI mode is investigated by experimental and computational methods. A sequential coupling approach of 3D CFD with a Stochastic Reactor Model (SRM) is used to simulate the PCCI engine. The SRM accounts for detailed chemical kinetics, convective heat transfer and turbulent micro-mixing. In this integrated approach, the temperature-equivalence ratio statistics obtained using KIVA 3V are mapped onto the stochastic particle ensemble used in the SRM. The coupling method proved to be advantageous in terms of computational expense and emission prediction capability, as compared with direct coupling of CFD and chemical kinetics. The results show that the fuel rich pockets in the late injection timing are desirable for triggering auto-ignition and advancing the combustion phasing. Furthermore, the model is utilised to study the impact of combustion chamber design (open bowl, vertical side wall bowl and re-entry bowl) on PCCI combustion and emissions. The piston bowl geometry was observed to influence the in-cylinder mixing and the pollutant formation for the conditions studied.
The demand for transport energy is increasing, but this increase is heavily skewed toward heavier fuels such as diesel
and jet fuel while the demand for gasoline might decrease. As spark-ignition engines develop to become more efficient,
abnormal combustion such as knock and preignition will become more likely. High antiknock quality fuels, those with
high research octane number and preferably low motor octane number, will enable future spark-ignition engines to reach
their full potential. Higher fuel antiknock quality is also likely to mitigate ‘‘superknock’’ resulting from preignition—an
abnormal combustion problem in turbocharged spark-ignition engines. In many parts of the world, fuel antiknock specifications
are set on the assumption that higher motor octane number contributes to increased knock resistance.
Specifications for fuel antiknock quality have a great impact on fuels manufacture and will need to be revised as this mismatch
between existing specifications and engine requirements widens. The primary challenge for diesel engines is to
reduce emissions of soot and NOx while maintaining high efficiency, and this becomes much easier if such engines are
run on fuels of extremely low cetane. Significant development is needed before such engines can be seen on practical
vehicles. In the long term, compression ignition engines are likely to use fuels with research octane number in the range
of 70–85 (cetane number\;30) but with no strict requirements on volatility. Such fuels would require less processing
in the refinery than today’s fuels. Such an engine/fuels system will be at least as efficient as today’s diesel engine but could
be significantly cheaper and also open a path to mitigate the imbalance in demand growth between heavy and light fuels
that is expected to arise otherwise. The review concludes with a possible long-term fuel scenario.
SAE 2007-01-0006
A Swedish MK1 diesel fuel and a European gasoline of
~95 RON have been compared in a single cylinder CI
engine operating at 1200 RPM with an intake pressure
of 2 bar abs., intake temperature of 40°C and 25%
stoichiometric EGR at different fuelling rates and using
different injection strategies. For the same operating
conditions, gasoline always gives much lower smoke
compared to the diesel fuel because of its higher ignition
delay; this usually allows the heat release to be separate
in time from the injection event. NOx can be controlled
by EGR. With dual injection, for diesel fuel, there can be
significant heat release during the compression stroke
because of the pilot injection earlier in the compression
stroke. For a fixed total fuelling rate, compared to single
injection, this reduces fuel efficiency and increases the
lowest achievable level of smoke. With gasoline, pilot
injection helps reduce the maximum heat release rate
for a given IMEP and enables heat release to occur later
with low cyclic variation compared to single injection.
This enables higher mean IMEP to be reached with
lower smoke, NOx and maximum heat release rate
compared to single injection. One of the operating points
reached with gasoline with double injection had mean
IMEP of 15.95 bar (stdev. 0.112 bar), AVL smoke
opacity of 0.33% (FSN < 0.07), ISNOx of 0.58 g/kWh,
ISFC of 179 g/kWh, ISHC of 2.9 g/kWh, ISCO of 6.8
g/kWh and peak pressure of ~ 120 bar. At the same
operating conditions, to get such low level of smoke with
Swedish MK1 diesel fuel, IMEP has to be below 6.5 bar.
There is scope for further improvements by increasing
intake pressure and the EGR level and through
optimisation of the injection and mixture preparation
strategy e.g. more injection pulses and injector design
e.g. more holes.
If fuels that are more resistant to autoignition are injected near top dead centre in compression ignition engines, they ignite much later than diesel fuel does, and combustion occurs when the fuel and air have had more chance to mix. This helps to reduce nitrogen oxide and smoke emissions. Moreover, this can be achieved at much lower injection pressures than for a diesel fuel. However, it is preferable to have fuels with a lower research octane number than those of commonly available gasolines, because this makes low-load operation easier while retaining the advantages at higher loads. A practical approach to making such fuels is to blend the gasoline and diesel fuel available in the market. Such fuel blends have a wide volatility range since they contain high-boiling-point components from the diesel but have a lower research octane number than that of the gasoline used but have a much longer ignition delay than that of the diesel fuel. This work describes the results of running a single-cylinder diesel engine on three such fuel blends. The engine could be run on such blends with extremely low smoke and low nitrogen oxide emissions at speeds of up to 4000 r/min and loads (indicated mean effective pressures) of up to 10 bar with an injection pressure of only 400 bar. The smoke levels at comparable nitrogen oxide levels were extremely high with diesel fuel in these conditions, even with an injection pressure of 1100 bar. The engine could also be run at near-idle conditions on these blends but with higher hydrocarbon and carbon monoxide emissions but much lower nitrogen oxide emissions and maximum pressure rise rate compared with those of the diesel fuel. The wider volatility range might be of benefit in avoiding over-mixing and over-leaning, which could lead to poor combustion stability. The paper also considers the trade-offs between the nitrogen oxide, smoke, hydrocarbon and carbon monoxide emissions and the maximum pressure rise rate and discusses approaches to optimise this type of combustion.
Fuels that are more resistant to autoignition allow more time for mixing before combustion occurs and help to reduce nitrogen oxides (NOx) and smoke in a diesel engine. However, hydrocarbon (HC) and carbon monoxide (CO) emissions are high at low loads because combustion is more likely to take place in lean mixture packets with better mixing caused by longer ignition delays. These problems can be significantly alleviated by managing the mixture strength by changing the injection pressure and the nozzle geometries. A single-cylinder diesel engine is run on a mixture of gasoline and diesel with a research octane number of 91, at different speeds, loads, and exhaust gas recirculation levels using three different nozzles. It is much easier to obtain low NOx and low smoke emissions with this fuel than with a European diesel fuel using the standard nozzle. Larger injector holes and lower injection pressures help to reduce the HC and CO emissions at low loads and also enable the gasoline-like fuel to run at a higher speed of 4000 r/min at a reasonably high load (indicated mean effective pressure) of 10 bar.
A comparative study using diesel fuel and gasoline has been conducted focusing on the injection process. In this paper an experimental study has been carried out comparing the effects of the different fuels on the mass flow rate, momentum flux and spray visualization in non-reactive conditions with a conventional common rail system with a multi-hole injector and two different nozzle designs. Analysis of the results for both fuels show no significant variations of the momentum flux between fuels while mass flow appears to be higher for diesel with respect to gasoline when the injector needle is fully open. The use of gasoline in these injectors seems relevant in the opening and closing phases of the injector. The high-speed imaging under non-evaporative conditions revealed that both diesel and gasoline spray penetration are “quite” similar and the statistical analysis of the results shows good agreement with the literature, furthermore new parametric correlation for gasoline is presented in this work. No major differences in the spray cone angle have been found either, showing consistency with the momentum flux measurements.
Previous work has showed that it may be advantageous to use fuels of lower cetane numbers compared to today’s diesel fuels in compression ignition engines. The benefits come from the longer ignition delays that these fuels have. There is more time available for the fuel and air to mix before combustion starts which is favourable for achieving low emissions of NOx and smoke though premixing usually leads to higher emissions of CO and unburned hydrocarbons.
In the present work, operation of a single-cylinder light-duty compression ignition engine on four different fuels of different octane numbers, in the gasoline boiling range, is compared to running on a diesel fuel. The gasoline fuels have research octane numbers (RON) of 91, 84, 78, and 72. These are compared at a low load/low speed condition (4 bar IMEP / 1200 rpm) in SOI sweeps as well as at a higher load and speeds (10 bar IMEP / 2000 and 3000 rpm) in EGR sweeps. There is a NOx advantage for the 91 RON and 84 RON fuels at the lower load. At the higher load, NOx levels can be reduced by increasing EGR for all gasolines while maintaining much lower smoke levels compared to the diesel. In the conditions studied, the optimum RON range might be between 75 and 85.
Gasoline compression ignition (GCI) is a promising advanced combustion mode to improve the fuel economy and reduce emissions. The intake conditions have significant effects on GCI combustion. To explore the proper intake conditions and fuels to achieve high efficiency under all loads, several experimental tests were carried out to investigate the effects of intake pressure and intake temperature on GCI combustion and emissions in this paper. Four primary reference fuels (PRF) with the research octane number (RON) of 90, 80, 70 and 60 were applied in this paper, which are recorded as PRF90, PRF80, PRF70 and PRF60. The results show that high efficiency under all loads could be achieved indeed by choosing proper intake pressure, intake temperature and fuels. The increase in intake pressure could significantly improve the fuel economy and decrease the CO, THC and NOx emissions. The increase in intake temperature increased the thermal efficiency under low loads and decreased the CO and THC emissions, but increased the NOx emissions simultaneously. However, with the increase in loads, the increased intake temperature reduced the volumetric efficiency, thus worsening the fuel economy. In addition, the influence of intake temperature on GCI combustion decreased with the decrease in RON. In general, high efficiency could be achieved by applying PRF70 and intake heating under low loads, as well as PRF70 under medium loads and PRF90 under high loads without intake heating, combined with supercharge under all loads. The highest indicated thermal efficiency (ITE) could reach 47% with PRF70 under medium loads.
Particulates emission is a common problem for both conventional compression ignition (CI) and spark ignition (SI) engines, and it creates issues related to environment, human health, and engine efficiency. For particulate reduction, the use of after-treatment systems/devices has been debated since last two decades; however, cost and system complexity issues are the main hurdles for adaptation of these systems in the engines. Therefore, advanced combustion technologies have been developed to achieve cleaner combustion, especially lower oxides of nitrogen (NOx) and particulates. Most of these advanced combustion strategies are categorized as low temperature combustion (LTC). LTC is a novel combustion technology, in which simultaneous reduction of NOx and particulates can be achieved without affecting the engine performance. LTC strategies include mainly homogeneous charge compression ignition (HCCI), partially-premixed charge compression ignition (PCCI), and reactivity controlled compression ignition (RCCI) combustion. In LTC strategies, early fuel injection provides sufficient time for fuel–air mixing before combustion, or a homogeneous fuel–air mixture is supplied to the combustion chamber, which results in complete absence of fuel-rich regions, leading to lower particulate formation. This chapter discusses all these advanced combustion technologies and describes the effect of different control parameters on particulate characteristics emitted from these strategies. A section including particulate formation mechanism and its structure has been included in this chapter for better understanding of the effects of different parameters on particulate emissions. This chapter presents the current technology status and the future research directions for these technologies so that these combustion concepts can be adapted for developing new generation vehicles.
Gasoline compression ignition (GCI) is a promising combustion concept with high thermal efficiency, low emissions, and minimal modification of standard engine hardware. With a relaxed constraint on the engine-out NOx emissions, different GCI operating parameters such as exhaust gas recirculation (EGR), injection timing, injection pressure, pilot-main injection interval, and pilot mass were swept to find their optimal calibrations. The entire operating map of a heavy duty diesel engine using GCI combustion with multi-injection strategies was also investigated. Results show that the use of pilot injection is effective in controlling the premixing heat release rate, reducing the combustion noise and emissions, and improving controllability, and allows for advancing combustion timing within the imposed mechanical constrains. With the engine-out NOx calibration of around 4.5 g/kW-h for typical Euro 6 compliant engines, the double injection strategy is applied over the entire operating map in GCI mode, and similar engine performance and emissions can be achieved by GCI combustion compared to conventional diesel combustion (CDC) mode, just using lower injection pressures. The peak brake thermal efficiency (BTE) of 44% over the entire operating map is demonstrated with minimal pumping and friction losses while keeping the peak cylinder pressure (PCP) within 16 MPa.
Fuel efficiency and emission performance sensitivity to fuel reactivity was examined using Delphi’s second-generation Gasoline Direct-Injection Compression Ignition (Gen 2.0 GDCI) multi-cylinder engine. The study was designed to compare a US market gasoline (RON 92 E10) to a higher reactivity gasoline (RON 80) at four operating conditions ranging from light load of 800 rpm / 2.0 bar gross indicated-mean-effective pressure (IMEPg) to medium load of 2000 rpm / 10.0 bar IMEPg. The experimental assessment indicated that both gasolines could achieve good performance and Tier 3 emission targets at each of the four operating conditions. Relative to the RON 92 E10 gasoline, better fuel consumption and engine-out emissions performance was achieved when using RON 80 gasoline; consistent with our previously reported single-cylinder engine research [1]. More specifically, a fuel consumption improvement was observed at the low load operating conditions (800 rpm / 2.0 bar IMEPg and 2000 rpm / 2.6 bar IMEPg) when using the RON 80 gasoline, compared to using market RON 92 E10 gasoline mainly due to better combustion stability that is directly associated with the fuel’s higher reactivity. For mid-load operation (1500 rpm / 6.0 bar IMEPg and 2000 rpm / 10.0 bar IMEPg), significantly lower fuel consumption was achieved when using the higher reactivity (RON 80) gasoline due to significantly lower boost pressure requirements and an enhanced combustion process. Clear differences in low temperature heat release (LTHR) behavior for this partially premixed compression ignition (PPCI) combustion process was also observed between the two gasolines. Specifically for the Delphi Gen 2.0 GDCI multi-cylinder engine, fuel consumption and engine-out emission targets were able to achieve when using both current market RON 92 E10 gasoline and a higher reactivity RON 80 gasoline. Furthermore, the higher reactivity RON 80 gasoline exhibited further improvement of light-to-medium load performance and emissions.
The present study aims to evaluate the effects of engine speed on gasoline compression ignition (GCI) combustion implementing double injection strategies. The double injection comprises of near-BDC first injection for the formation of a premixed charge and near-TDC second injection for the combustion phasing control. The engine performance and emissions testing of GCI combustion has been conducted in a single-cylinder light-duty diesel engine equipped with a common-rail injection system and fuelled with a conventional gasoline with 91 RON. The double injection strategy was investigated for various engine speeds ranging 1200~2000 rpm and the second injection timings between 12°CA bTDC and 3°CA aTDC. From the tests, GCI combustion shows high sensitivity to the second injection timing and combustion phasing variations such that the advanced second injection causes advanced combustion phasing and extended pre-combustion mixing time, and thereby increasing engine efficiency and decreasing ISFC. This leads to the reduced smoke/ uHC/CO emissions but increased combustion noise and NOx emissions, similar to the trends in conventional diesel combustion. It is found that the increased engine speed requires a higher fuel mass per injection to maintain similar IMEP values, leading to lower efficiency, higher ISFC, and increased combustion noise. The heat release rate increases with increasing engine speed but the combustion phasing is largely unchanged. A typical smoke-NOx trade-off is found with increased smoke and decreased NOx emissions at higher engine speed, primarily due to reduced charge premixing time, which suggests the partially premixed charge-based GCI combustion behaves similar to conventional diesel combustion with overall lower smoke and NOx emissions.
Gasoline Compression Ignition (GCI) engines using a low octane gasoline-like fuel (LOF) have good potential to achieve lower NOx and lower particulate matter emissions with higher fuel efficiency compared to the modern diesel compression ignition (CI) engines. In this work, we conduct a well-to-wheels (WTW) analysis of the greenhouse gas (GHG) emissions and energy use of the potential LOF GCI vehicle technology. A detailed linear programming (LP) model of the US Petroleum Administration for Defense District Region (PADD) III refinery system - which produces more than 50% of the US refined products - is modified to simulate the production of the LOF in petroleum refineries and provide product-specific energy efficiencies. Results show that the introduction of the LOF production in refineries reduces the throughput of the catalytic reforming unit and thus increases the refinery profit margins. The overall efficiency of the refinery does not change significantly because both the purchased energy and the refinery fuel production increase in response to the introduction of the LOF production. The refinery energy efficiency of LOF is approximately 0.8 and 1.6 percentage points higher than that of gasoline and diesel, respectively. Taking into account a 25% fuel economy gain relative to the regular gasoline internal combustion engine vehicle (ICEV), the per-mile-based WTW GHG emissions of the LOF GCI ICEV are estimated to be 22% and 9% lower than those of the today’s gasoline and diesel ICEVs, respectively; and the per-mile-based WTW fossil energy use is 18% and 6% lower than gasoline and diesel ICEVs, respectively.
The use of low-octane gasoline on Gasoline Compression Ignition (GCI) engines is considered as a competitive alternative to the conventional vehicle propulsion technologies. In this study, a process-based, well-to-wheel conceptualized life cycle assessment model is established to estimate the life cycle energy consumption and greenhouse gas (GHG) emissions of the conventional gasoline-Spark Ignition (SI) and low-octane gasoline-GCI pathways. It is found that compared with the conventional pathway, the low-octane gasoline-GCI pathway leads to a 24.6% reduction in energy consumption and a 22.8% reduction in GHG emissions. The removal of the isomerization and catalytic reforming units in the refinery and the higher energy efficiency in the vehicle use phase are the substantial drivers behind the reductions. The results indicate that by promoting the use of low-octane gasoline coupled with the deployment of GCI vehicles, considerable reductions of energy consumption and GHG emissions in the transport sector can be achieved. However, significant technical and market barriers are still to be overcome. The inherent problems of NOx and PM exhaust emissions associated with GCI engines need to be further addressed with advanced combustion techniques. Besides, the yield of low-octane gasoline needs to be improved through adjusting the refinery configurations.
Gasoline Direct Injection Compression Ignition (GDCI) is a partially premixed low temperature combustion process that has demonstrated high fuel efficiency with full engine load range capabilities, while emitting very low levels of particulate matter (PM) and oxides of nitrogen (NOx). In the current work, a comparison of engine combustion, performance, and emissions has been made among E10 gasoline and several full-boiling range naphtha fuels on a Gen 2 single-cylinder GDCI engine with compression ratio of 15:1. Initial results with naphtha demonstrated improved combustion and efficiency at low loads. With naphtha fuel, hydrocarbon and carbon monoxide emissions were generally reduced at low loads but tended to be higher at mid-loads despite the increased fuel reactivity. At higher loads, naphtha required less boost pressure compared to gasoline, however, up to 20% additional EGR was required to maintain combustion phasing. The higher reactivity of naphtha did cause some reduction of peak load for the operating strategy tested, when constrained to the targets used in this study. For all fuels, particle size distributions were bimodal and had similar numbers of particles larger than 40 nm, while there were some differences in numbers of smaller particles. Based on an efficiency loss analysis, the fuels exhibited generally similar performance over the load range.
Partially Premixed Combustion (PPC) provides the potential of simultaneous reduction of NOx and soot for diesel engines. This work attempts to characterize the operating range and conditions required for PPC. The characterization is based on the evaluation of emission and in-cylinder measurement data of engine experiments. It is shown that the combination of low compression ratio, high EGR rate and engine operation close to stoichiometric conditions enables simultaneous NOx and soot reduction at loads of 8bar, 12bar, and 15bar IMEP gross. The departure from the conventional NOx-soot trade-off curve has to be paid with a decline in combustion efficiency and a rise in HC and CO emissions. It is shown that the low soot levels of PPC come along with long ignition delay and low combustion temperature. A further result of this work is that higher inlet pressure broadens the operating range of Partially Premixed Combustion.
In recent years several new gasoline engine technologies were introduced in order to reduce fuel consumption. Controlled autoignition seems to be an alternative to stratified part load operation, which is handicapped due to it's lean aftertreatment system for world wide application. The principal advantages of controlled auto ignition combustion under steady state operation - combining fuel economy benefits similar to stratified charge systems with nearly negligible NOx and soot emissions -are already well known. With the newly developed AVL- CSI system (Compression and Spark Ignition), a precise combustion control is achieved even under transient operation. For compensation of production and operation tolerances a cost optimized cylinder individual control was developed. Completely new functionalities of the engine management system are applied. This lean GDI concept complies with future emission standards without DeNOx catalyst and can be applied worldwide. This paper covers the practical application of the AVL CSI combustion system including the required valve actuation variability and the demanded control system for the real world operation in a passenger car vehicle.
Gasoline compression ignition (GCI) engines could be more efficient than most advanced SI engines while running on lower octane fuel. GCI engines may utilize a mixture of different fuels and fuel components such as gasoline and diesel or diesel and naphtha. The risks and hazards associated with such mixtures must be studied to ensure safe fuel storage, shipping and dispensing. In this work, flash point and vapor pressure measurements of different binary multi-component hydrocarbon mixtures are presented along with calculated lower and upper flammability limits. An equation has been developed to correlate flash point with other fuel properties. The flash point of a mixture approaches the flash point of the more volatile component, falling rapidly in some cases, as the more volatile component concentration increases. Vapor pressure is inversely related to flash point for a given mixture. Diesel/light straight run naphtha mixtures and diesel/gasoline mixtures exhibit similar flash point versus vapor pressure trends. Flammability limits were calculated using Le Chatelier’s Mixing Rule and modified Burgess–Wheeler Law. Hydrocarbon mixtures have similar lower and upper flammability limits over a range of temperatures. The vapor pressure of fuels and fuel blends has been used to determine the safe operating region as a function of blending formula and temperature. This work demonstrates that normal butane can be used to formulate blends of gasoline and naphtha with diesel, which are safe to handle and meet seasonal vapor pressure requirements.
The Premixed Charge Compression Ignition (PCCI) engine has the potential to reduce soot and NO x emissions while maintaining high thermal efficiency at part load conditions. However, several technical barriers must be overcome. Notably ways must be found to control ignition timing, expand its limited operation range and limit the rate of heat release. In this paper, comparing with single fuel injection, the superiority of multiple-pulse fuel injection in extending engine load, improve emissions and thermal efficiency trade-off using high exhaust gas recirculation (EGR) and boost in diesel PCCI combustion is studied by engine experiments and simulation study. It was found that EGR can delay the start of hot temperature reactions, reduce the reaction speed to avoid knock combustion in high load, is a very useful method to expand high load limit of PCCI. EGR can reduce the NO x emission to a very small value in PCCI. At low engine load using high EGR, low soot, CO, UHC and NO x emissions can be simultaneously achieved. There are no significantly differences in mixture formation before ignition, emissions and thermal efficiency using single and multi-injection at low load. At low load, with the increase of EGR rate, smoke emission of PCCI doesn't increase obviously because the homogeneous mixture avoids fuel-rich. At higher engine load with high EGR, the localization of single injection in extending operation range is the high soot, CO and UHC emissions; using multi-injection mode, the CO and UHC emissions are decreased with little expense of NO x emissions. Comparing with single injection, multi-injection is more beneficial for lean and homogenous mixture formation, especially at high load. With intake boost using multi-injection, the engine load can be further extended; despite the ignition time is advanced, the leanness and homogeneity of the mixture are improved; the indicated thermal efficiency is increased, and the CO and soot emissions are greatly decreased with not large expense of NO x emissions. Using PCCI with high EGR and boost, the IMEP of the engine can be further extended to 1.01 MPa, while keeping near to zero emissions and high thermal efficiency up to 47%.
A broad range of diesel, kerosene, and gasoline-like fuels has been tested in a single-cylinder diesel engine optimized for advanced combustion performance. These fuels were selected in order to better understand the effects of ignition quality, volatility, and molecular composition on engine-out emissions, performance, and noise levels. Low-level biofuel blends, both biodiesel (FAME) and ethanol, were included in the fuel set in order to test for short-term advantages or disadvantages. The diesel engine optimized in Part 1 of this study included cumulative engine hardware enhancements that are likely to be used to meet Euro 6 emissions limits and beyond, in part by operating under conditions of Homogeneous Charge Compression Ignition (HCCI), at least over some portions of the speed and load map.
A gasoline compression-ignition combustion system is being developed for full-time operation over the speed-load map. Low-temperature combustion was achieved using multiple late injection (MLI), intake boost, and moderate EGR for high efficiency, low NOx, and low particulate emissions. The relatively long ignition delay and high volatility of RON 91 pump gasoline combined with an advanced injection system and variable valve actuation provided controlled mixture stratification for low combustion noise. Tests were conducted on a single-cylinder research engine. Design of Experiments and response surface models were used to evaluate injection strategies, injector designs, and various valve lift profiles across the speed-load operating range. At light loads, an exhaust rebreathing strategy was used to promote autoignition and maintain exhaust temperatures. At medium loads, a triple injection strategy produced the best results with high thermal efficiency. Detailed heat release analysis indicated that heat losses were significantly reduced. At higher loads, a late-intake-valve-closing strategy was used to reduce the effective compression ratio. For all tests, intake air temperature was 50 C. 3D CFD simulations of fuel injection, mixing, and combustion were important to understand the emissions formation processes. With multiple late injections and low-to-moderate fuel pressure, spray penetration was low, mixing was fast, and wall wetting could be avoided. Fuel sprays were characterized in a spray chamber. Injection rate was measured using a rate tube. Results showed that ISFC was very low. Minimum ISFC of 181 g/kWh was measured at 2000 rpm-11 bar IMEP. For IMEP from 2 to 18 bar, engine-out NOx and PM emissions were below targets of 0.2 g/kWh and 0.1 FSN, respectively, indicating that aftertreatment for these species may be reduced or eliminated. It was found that combustion noise levels, characterized by several noise metrics, could be effectively controlled by the injection process. Measurements of exhaust particulate size distribution indicated very low particle count, especially for a preferred injector with low levels of in-cylinder swirl. Collectively, these results demonstrate the potential feasibility of full-time GDCI using RON 91 gasoline at low-to-moderate injection pressures with high fuel efficiency. While more development work is needed, there is good potential for a practical GDCI powertrain system based on these concepts.
An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline injected using a triple-pulse strategy in the low temperature combustion (LTC) regime is presented. This work aims to extend the operation ranges for a light-duty diesel engine, operating on gasoline, that have been identified in previous work via extended controllability of the injection process. The single cylinder engine (SCE) was operated at full load (16 bar IMEP, 2500 rev/min) and computational simulations of the in-cylinder processes were performed using a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion chosen to match ignition characteristics of the gasoline fuel used for the SCE experiments. With constraints on a minimum allowable combustion efficiency, maximum allowable noise level (pressure rise rate) and maximum allowable NOx and soot emissions, engine operation ranges were identified as functions of injection timings and the fuel split ratio (i.e., fraction of total fuel injected in each pulse) with triple-pulse injections. Parametric variation of the engine operating ranges were also investigated with respect to initial (i.e., intake) gas temperature, exhaust gas recirculation ratio, intake boost pressure and injection system rail pressure. Following the modeling, engine experiments were performed under conditions identified through analysis of the numerical results in order to confirm the effectiveness of gasoline direct injection compression ignition (GDICI or GCI) operation with triple-pulse injections at full load. Based on both computational and experimental results, the role of each pulse in GDICI operation was identified in terms of combustion stability, engine performance and emissions. While maintaining similar emissions characteristics to that of the double-pulse injection cases (∼0.1 g/kg-f of NOx and PM, and ∼173 g/kW-hr of ISFC), the extension of operable conditions using a triple-pulse injection strategy was successfully achieved.
Low-temperature gasoline combustion (LTGC), based on the compression ignition of a premixed or partially premixed dilute charge, can provide thermal efficiencies (TE) and maximum loads comparable to those of turbo-charged diesel engines, and ultra-low NOx and particulate emissions. Intake boosting is key to achieving high loads with dilute combustion, and it also enhances the fuel's autoignition reactivity, reducing the required intake heating or hot residuals. These effects have the advantages of increasing TE and charge density, allowing greater timing retard with good stability, and making the fuel ϕ- sensitive so that partial fuel stratification (PFS) can be applied for higher loads and further TE improvements. However, at high boost the autoignition reactivity enhancement can become excessive, and substantial amounts of EGR are required to prevent overly advanced combustion. Accordingly, an experimental investigation has been conducted to determine how the tradeoff between the effects of intake boost varies with fuel-type and its impact on load range and TE. Five fuels are investigated: a conventional AKI=87 petroleum-based gasoline (E0), and blends of 10 and 20% ethanol with this gasoline to reduce its reactivity enhancement with boost (E10 and E20). A second zero-ethanol gasoline with AKI=93 (matching that of E20) was also investigated (CF-E0), and some neat ethanol data are also reported.
Results show that ethanol content has little effect on LTGC autoignition reactivity for naturally aspirated operation, but it produces a large effect for boosted operation, with the reactivity enhancement with boost being reduced by an amount that correlates with ethanol content. In contrast, CFE0 showed a reactivity enhancement with boost similar to E0. Related to this autoignition enhancement, the effect of fuel-type on the increase in ITHR with boost was also investigated since it correlates with the ability to retard CA50 with good stability for higher loads without knock and to apply PFS effectively. The study showed that by adding ethanol, less EGR is required with boost, leaving more oxygen available for combustion. As a result, the high-load limit could be increased from 16.3 to
18.1 to 20.0 bar IMEPg for E0, E10, and E20, respectively, and to 17.7 bar for the high-AKI gasoline. TE vs. load curves for the various fuels at typical boosted conditions are also presented and discussed. At boosted conditions, PFS was found to be very effective
for increasing the TE, with the peak TE increasing from 47.8% for premixed fueling to 48.4% with PFS, and TE improvements up to 2.8 %-units were achieved at higher loads.
An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections. Parametric variation of the operation ranges was also investigated with respect to initial gas temperature, boost pressure and injection pressure. Following the modeling, experiments were performed under the conditions suggested by the numerical results in order to confirm the feasibility of GDICI operation at full load, as well as to validate the numerical simulations. The results showed good agreement between the experiments and the model predictions. Due to the high volatility and low cetane index of gasoline combined with reduction of combustion temperature through utilization of EGR, both PM and NOx emissions could be reduced to levels of about 0.1 g/kg-f while maintaining experimental gross ISFC at about 180 g/kw-hr. The numerical simulations helped to explain the in-cylinder spray combustion behavior and to identify characteristics of GDICI that differ from those of diesel-fueled operation. Maps of operable conditions were generated that allow extension of low-emission engine concepts to full load operation in high speed GDICI engine operation with fuel efficiencies comparable to those of corresponding diesel fuel operation while meeting emissions mandates in-cylinder.
The spray and combustion characteristics of gasoline and diesel were investigated in a direct injection compression ignition engine equipped with a common rail injection system. The spray evolution was observed under a non-evaporating condition in a constant volume chamber and under an evaporating condition in an optical engine. Under the non-evaporating condition, the liquid penetration length was similar between the gasoline and diesel. The gasoline spray exhibited a relatively larger spray cone angle than that of diesel spray. However, the gasoline spray exhibited a significantly shorter liquid penetration length and narrower spray angle than that of the diesel spray under the evaporating condition. The maximum liquid penetration length was maintained constant regardless of the injection pressure for each fuel at the evaporating condition. The diesel spray formed wall wetting through the fuel impingement on the combustion chamber due to the long liquid penetration length at an early injection timing of −32 crank angle degree after top dead center (CAD ATDC).
The effects of fuel properties on the performance and emissions of an engine running in partially premixed combustion mode were investigated using nine test fuels developed in the gasoline boiling point range. The fuels covered a broad range of ignition quality and fuel chemistry. The fuels were characterized by performing a load sweep between 1 and 12 bar gross IMEP at 1000 and 1300 rpm. A heavy duty single cylinder engine from Scania was used for the experiments; the piston was not modified thus resulting in the standard compression ratio of 18:1. In order to properly run gasoline type of fuels in partially premixed combustion mode, an advanced combustion concept was developed. The concept involved using a lot of EGR, very high boost and an advanced injection strategy previously developed by the authors. By applying this concept all the fuels showed gross indicated efficiencies higher than 50% with a peak of 57% at 8 bar IMEP. NOx were mostly below 0.40 g/kWh only in few operative points 0.50 g/kWh was reached. At high load the soot levels were mostly a function of the octane number; with RON higher than 95 it was possible to be below 0.5 FSN while for the more reactive fuels a peak value of 3 FSN was reached at 13 bar IMEP. The pressure rise rate reached a peak of 19 bar/CAD with fuels which had a RON above 95, when the octane number decreased below 90 the pressure rise rate was always below 14 bar/CAD.
Partially Premixed Combustion (PPC) is a combustion concept by which it is possible to get low smoke and NOx emissions simultaneously. PPC requires high EGR levels to extend the ignition delay so that air and fuel mix prior to combustion to a larger extent than with conventional diesel combustion. This paper investigates the operating region of single injection PPC for three different fuels; Diesel, low octane gasoline with similar characteristics as diesel and higher octane standard gasoline. Limits in emissions are defined and the highest load that fulfills these requirements is determined. The investigation shows the benefits of using high octane number fuel for Multi-Cylinder PPC. With high octane fuel the ignition delay is made longer and the operating region of single injection PPC can be extended significantly. Experiments are carried out on a multi-cylinder heavy-duty engine at low, medium and high speed.
Partially premixed combustion (PPC) has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective of this study is investigation of the low load limitations with gasoline fuels with octane numbers RON 69 and 87. Measurements with diesel fuel were also taken as reference. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. Trapped hot residual gases using negative valve overlap (NVO) is the main parameter of interest to potentially increase the attainable operating region of high octane number gasoline fuels. Much lower soot is emitted with 69 and 87 RON gasoline compared to diesel at engine loads 1 bar IMEPgross to 3 bar IMEPgross but the combustion efficiency is significantly lower with gasoline at low load compared to diesel. Combustion efficiency increases with NVO for both diesel and gasoline. The 69 RON gasoline fuel can be run at idle (1 bar IMEPgross) operating conditions without a significant fraction of trapped hot residual gases. The 87 RON gasoline fuel could be run at 2 bar IMEPgross but with a high setting of NVO. There is a clear decrease of net indicated efficiency with NVO because of the decrease in gas-exchange efficiency. To achieve highest possible efficiency for a given fuel, at low load, as low as possible NVO should be used.
This paper is the follow up of a previous work and its target is to demonstrate that the best fuel for a Compression Ignition engine has to be with high Octane Number. An advanced injection strategy was designed in order to run Gasoline in a CI engine. At high load it consisted in injecting 54 % of the fuel very early in the pilot and the remaining around TDC; the second injection is used as ignition trigger and an appropriate amount of cool EGR has to be used in order to avoid pre-ignition of the pilot. Substantially lower NOx, soot and specific fuel consumption were achieved at 16.56 bar gross IMEP as compared to Diesel. The pressure rise rate did not constitute any problem thanks to the stratification created by the main injection and a partial overlap between start of the combustion and main injection. Ethanol gave excellent results too; with this fuel the maximum load was limited at 14.80 bar gross IMEP because of hardware issues. Applying the commonly used PPC injection strategies to Gasoline resulted in higher pressure oscillations after combustion and the heat transfer was enhanced. It was shown that this problem can be somehow solved by employing a late pilot injection, unfortunately the combustion is diffusion controlled and there is an increase in fuel consumption as compared to the strategy previously described. The viability of having low fuel consumption, NOx, soot and pressure rise rate using high ON fuels in a CI engine was demonstrated using a Scania single cylinder truck engine with 2 liters displacement volume running at 1100 rpm. (Less)
Gasoline partially premixed combustion showed the potential of very high efficiency, emissions of nitrogen oxides (NO x ) and soot below future emission regulations, and acceptable acoustic noise from idle up to 26 bar gross indicated mean effective pressure. For instance, gross indicated efficiencies in the range of 53 to 55 per cent were achieved in the whole load range keeping NO x below 0.30 g/kWh, soot below 0.30 filter smoke number (FSN), and relative maximum pressure rise rate below 8 bar/crank angle degree. The goal was achieved by developing an appropriate EGR–λ (exhaust gas recirculation/relative excess of air) combination and an advanced injection strategy, and by making minor modifications to the engine layout.
The current paper presents a summary of the advantages of using gasoline-type fuels (research octane number (RON) from 80 to 69) in a heavy-duty compression ignition engine. Low-octane-number gasoline fuels were chosen because they can run from idle to maximum load without any major modification to the engine layout and because low-load operations are achievable even when the engine is cold and the inlet temperature is low. Experiments were carried out in two single-cylinder engines, Scania D12 and Scania D13, using a total of three different engine setups. The influence of different types of gasoline (RON from 99 to 69) on this novel combustion concept was analysed. A comparison between gasoline and diesel fuels is presented and the viability of reaching 50 per cent brake efficiency while keeping low emissions of NO x and soot is shown.
A light-duty diesel engine has been operated in advanced combustion modes known generally as premixed charge compression ignition (PCCI). The emissions have been characterized for several load and speed combinations. Fewer NOx and particulate matter (PM) emissions are produced by PCCI, but higher CO and hydrocarbon (HC) emissions result. In addition, the nature of the PM differs from conventional combustion; the PM is smaller and has a much higher soluble organic fraction (SOF) content (68% vs. 30% for conventional combustion). Three catalyst technologies were studied to determine the affects of HECC on catalyst performance; the technologies were a lean NOx trap (LNT), diesel oxidation catalyst (DOC), and diesel particulate filter (DPF). The LNT benefited greatly from the reduced NOx emissions associated with PCCI. NOx capacity requirements are reduced as well as overall tailpipe NOx levels particularly at low load and temperature conditions where regeneration of the LNT is difficult. The DOC performance requirements for PCCI are more stringent due to the higher CO and HC emissions; however, the DOC was effective at controlling the higher CO and HC emissions at conditions above the light-off temperature. Below light-off, CO and HC emissions are problematic. The study of DPF technology focused on the fuel penalties associated with DPF regeneration or “desoot” due to the different PM loading rates from PCCI vs. conventional combustion. Less frequent desoot events were required from the lower PM from PCCI and, when used in conjunction with an LNT, the lower PM from less frequent LNT regeneration. The lower desoot frequency leads a ∼3% fuel penalty for a mixture of PCCI and conventional loads vs. ∼4% for conventional only combustion.
The hollow-cone spray of a high-pressure swirl injector for a direct-injection spark-ignition (DISI) engine was investigated inside a pressure vessel by means of particle image velocimetry (PIV). As the interaction between the spray droplets and the ambient air is of particular interest for the mixture preparation process, two-phase PIV techniques were applied. To allow phase discrimination, fluorescent seeding particles were used to trace the gas phase. Because of the periodicity of piston engine injection, a statistical evaluation of ensemble-averaged fields to reduce cycle-to-cycle variations and to provide more general information about the two-phase flow was performed. Besides the general spray/air interaction process the investigation of the spray collapse at elevated ambient pressures was the main focus of the study. Future investigations of transient interaction processes require simultaneous techniques in combination with a high-speed camera to resolve the transient interaction phenomena. Therefore, optical filters that attenuate Mie-scattered light and transmit fluorescent light were used to collect both phases on the same image. Consequently, phase separation techniques were employed for data analysis. A masking and a peak separation technique are described and a comparison between the results of an instantaneous two-phase flow field in the spray cone of a DISI injector is presented in the paper.
Boosted HCCI-controlling pressure-rise rates for performance improvements using partial fuel stratification with conventional gasoline
- J E Dec
- Y Yang
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Dec JE, Yang Y, Dronniou N (2011) Boosted HCCI-controlling pressure-rise rates for performance improvements using partial fuel stratification with conventional gasoline. SAE Intl J Eng
4(1):1169-1189. https://doi.org/10.4271/2011-01-0
Outlook for Energy: a view to 2040
- Exxonmobil
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customerportal/publications/317291.pdf?modified=20180526153435. Accessed 16 June 2019
Homogeneous charge compression ignition (HCCI) of diesel fuel
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Gray III AW, Ryan III TW (1997) Homogeneous charge compression ignition (HCCI) of diesel
fuel. SAE Trans 1:1927-1935. https://www.jstor.org/stable/44730808
Development of Toyota’s direct injection gasoline engine
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