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Optimization of a High-Speed Dual-Fuel (Natural Gas-Diesel) Compression Ignition Engine for Gen-sets
... The work described in the paper consists of a 3D-CFD analysis, carried out by means of a customized version of KIVA-3V. As reported in a previous paper [23], the original diesel engine was modified in order to operate in DF NG-diesel mode. Then, a comprehensive experimental campaign was undertaken, at different operating conditions. ...
... Different DF operating points, varying both the engine load and the amount of diesel substitution with NG, were investigated. The results of the experimental campaign are reported in [23]. ...
The present work aims to assess the influence of the composition of blends of hydrogen (H2) and Natural Gas (NG) on Dual Fuel (DF) combustion characteristics, including gaseous emissions. The 3D-CFD study is carried out by means of a customized version of the KIVA-3V code. An automotive 2.8 L, 4-cylinder turbocharged diesel engine was previously modified in order to operate in DF NG–diesel mode, and tested at the dynamometer bench. After validation against experimental results, the numerical model is applied to perform a set of combustion simulations at 3000 rpm–BMEP = 8 bar, in DF H2/NG-diesel mode. Different H2–NG blends are considered: as the H2 mole fraction varies from 0 vol% to 50 vol%, the fuel energy within the premixed charge is kept constant. The influence of the diesel Start Of Injection (SOI) is also investigated. Simulation results demonstrate that H2 enrichment accelerates the combustion process and promotes its completion, strongly decreasing UHC and CO emissions. Evidently, CO2 specific emissions are also reduced (up to about 20%, at 50 vol% of H2). The main drawbacks of the faster combustion include an increase of in-cylinder peak pressure and pressure rate rise, and of NOx emissions. However, the study demonstrates that the optimization of diesel SOI can eliminate all aforementioned shortcomings.
... Fundamental in this case is the difference in the two concepts of converting diesel engines to a gas-diesel power model. The most radical method is the complete replacement of fuel, which is accompanied by spark ignition of the gas-air mixture (Mattarelli et al., 2021). This method involves complete disassembly of the diesel fuel equipment followed by reprogramming of the compression ratio, reducing it to 11-14 units, and at the end, the system is equipped with gas equipment (ignition system, cylinder, gas pipeline). ...
In conditions of constant growth in the cost of traditional oil products and their shortage, the issue of using alternative fuels becomes urgent. The purpose of the article is to identify ways of using alternative types of fuel for the operation of diesel engines. Research methods – analysis and verification of data obtained from scientific publications, which are part of the world-famous scient metric databases, for the relevance of the subject of research. The research results reveal the advantages and disadvantages of dual-fuel engines operating on gaseous fuel with diesel fuel additive, the impact of this type of engine on emissions and toxicity of exhaust gases, in particular nitrogen oxides NOx. The application of the so-called gas nozzle and the cross-section of the holes of its nozzles are substantiated. It was analysed and established that the most economically expedient is the use of liquefied petroleum gas for the operation of diesel engines by implementing the gas-liquid cycle; it was found that the most promising for this is gas cylinder equipment of the so-called 4th generation. A retrospective analysis of studies of internal combustion engines with gas cylinder equipment showed an increase in motor resource when using gaseous fuels, as well as the negative side of using gaseous fuels, which consists in reduced power when converting carburettor engines, however, the use of these fuels for the operation of diesel engines completely eliminates this disadvantage. Based on the research analysis, the influence of the ignition dose, when the engine is operating on the gas-diesel cycle, on the performance at different loads was also established, and a recommendation was found to switch to the diesel cycle from the gas-diesel cycle at loads less than 30% of the nominal one. The optimal scheme for the implementation of the gas-diesel cycle, which is relevant and promising for more widespread energy and transport vehicles, has been substantiated and selected. Based on the analysed schemes, it was established that the scheme that can be taken as a basis for further research in this direction is the scheme of the DG-Flex BOSCH gas-diesel system. The practical value of the work lies in the justification of complex conversion with partial replacement of diesel fuel with liquefied petroleum gas as the most rational way of converting serial diesel engines into dual-fuel engines
... In order to validate the 3D-CFD model employed in the study, a set of experimental data were used. Such data were collected during a comprehensive experimental campaign described in [57], carried out by the authors on an automotive turbocharged diesel engine, manufactured by FCA-VM Motori, whose main characteristics are reported in Table 1. ...
div>The numerical study presented in this article is based on an automotive diesel engine (2.8 L, 4-cylinder, turbocharged), considering a NG–H<sub>2</sub> blend with 30 vol% of H<sub>2</sub>, ignited by multiple diesel fuel injections. The 3D-CFD investigation aims at improving BTE, CO, and UHC emissions at low load, by means of an optimization of the diesel fuel injection strategy and of the in-cylinder turbulence (swirl ratio, SR). The operating condition is 3000 rpm – BMEP = 2 bar, corresponding to about 25% of the maximum load of a gen-set engine, able to deliver up to 83 kW at 3000 rpm (rated speed). The reference diesel fuel injection strategy, adopted in all the previous numerical and experimental studies, is a three-shot mode. The numerical optimization carried out in this study consisted in finding the optimal number of injections per cycle, as well as the best timing of each injection and the fuel mass split among the injections. The analysis revealed that combustion can be improved by increasing the local concentration of the more reactive fuel (diesel): in detail, the best strategy is a two-shot mode, with SOI1 = −35°CA AFTDC and SOI2 = −20°CA AFTDC, injecting 70% of the total diesel fuel mass at the first shot. As far as the SR is concerned, the best compromise between performance and emissions was found for a relatively low SR = 1.4. The optimization permitted to extract the full potential of the H<sub>2</sub> enrichment in the DF H<sub>2</sub>/NG–diesel combustion also at low loads: in comparison to the DF NG case, combustion efficiency, and gross indicated thermal efficiency have been improved by 45.7% and 61.0%, respectively; CO- and UHC-specific emissions have been reduced by about 85.0%. Comparing CDC to the optimized DF 30 vol% H<sub>2</sub>/NG–diesel case, soot emissions are completely canceled, CO<sub>2</sub>-specific emissions have been reduced by approximately 42.0%, NO<sub>x</sub>-specific emissions by 33.8%. However, further work has to be done in order to reach comparable values of HC and CO, which are still higher than in a standard diesel combustion.</div
... The development of a clean and efficient combustion system for a DF engine is typically based on the optimization of the composition of the premixed charge (air, BG and burnt gas) and the calibration of the injection strategy [21,22]. To reduce the cost, no modification is made to the combustion chamber geometry or the injector of the original diesel engine. ...
Micro-cogeneration with locally produced biogas from waste is a proven technique for supporting the decarbonization process. However, the strongly variable composition of biogas can make its use in internal combustion engines quite challenging. Dual-fuel engines offer advantages over conventional SI and diesel engines, but there are still issues to be addressed, such as the low-load thermodynamic efficiency and nitrogen oxide emissions. In particular, it is highly desirable to reduce NOx directly in the combustion chamber in order to avoid expensive after-treatment systems. This study analyzed the influence of the combustion system, especially the piston bowl geometry and the injector nozzle, on the performance and emissions of a dual-fuel diesel–biogas engine designed for micro-cogeneration (maximum electric power: 50 kW). In detail, four different cylindrical piston bowls characterized by radii of 23, 28, 33 and 38 mm were compared with a conventional omega-shaped diesel bowl. Moreover, the influence of the injector tip position and the jet tilt angle was analyzed over ranges of 2–10 mm and 30–120°, respectively. The goal of the optimization was to find a configuration that was able to reduce the amount of NOx while maintaining high values of brake thermal efficiency at all the engine operating conditions. For this purpose, a 3D-CFD investigation was carried out by means of a customized version of the KIVA-3V code at both full load (BMEP = 8 bar, 3000 rpm, maximum brake power) and partial load (BMEP = 4 bar, 3000 rpm). The novelty of the study consisted of the parametric approach to the problem and the high number of investigated parameters. The results indicated that the standard design of the piston bowl yielded a near-optimal trade-off at full load between the thermodynamic efficiency and pollutant emissions; however, at a lower load, significant advantages could be found by designing a deeper cylindrical bowl with a smaller radius. In particular, a new bowl characterized by a radius of 23 mm was equivalent to the standard one at BMEP = 8 bar, but it yielded a NOx-specific reduction of 38% at BMEP = 4 bar with the same value of BTE.
... 59 The study presented in this paper is carried out on a light-duty turbocharged Diesel engine, modified by the authors in order to operate in DF NG-diesel mode. The experimental characterization of the engine was fully described in a previous paper, 60 and it is employed here to support the validation of a numerical model, developed by using a commercial CFD-3D tool (ANSYS Forte). The operating point of interest corresponds to 3000 rpm-44 Nm/BMEP = 2 bar. ...
Dual Fuel (DF) combustion can help to reduce the environmental impact of internal combustion engines, since it may provide excellent Brake Thermal Efficiency (BTE) combined with ultra-low emissions. This technique is particularly attractive when using biofuels, or fuels with a low Carbon content, such as Natural Gas (NG). Unfortunately, as engine load decreases and the homogeneous NG-air mixture tends to become very lean, the high chemical stability of NG can be a serious obstacle to the completion of combustion. As a result, BTE drops and UHC and CO emissions become very high. A possible way to address this problem could be the addition of hydrogen (H 2 ) to the NG-air mixture. In this paper, a numerical study has been carried out on an automotive Diesel engine, modified by the authors in order to operate in both conventional Diesel combustion and DF NG-diesel mode. A previous experimental characterization of the engine is the basis for the CFD-3D modeling and calibration of the DF combustion process, using a commercial software. The effects on combustion stability and emissions of different NG-H 2 mixtures (six blends with 5%, 10%, 15%, 20%, 25%, and 30% by volume of hydrogen) are numerically investigated at a low load (BMEP = 2 bar, engine speed 3000 rpm). The results of the CFD-3D simulations demonstrate that NG-H 2 blends are able to decrease strongly CO, UHC, and CO 2 emissions at low loads. Advantages are also found in terms of thermal efficiency and NO x emissions.
... The development of the engine is mainly based on a comprehensive experimental campaign, carried out on another version of the DF engine, running on Diesel fuel and NG [20]. The collected experimental data are used to calibrate and validate a CFD-3D combustion model; then, this model is applied to the theoretical study of DF combustion, with different compositions of biogas. ...
Renewable sources and enhancement of energy conversion efficiency are the main paths chosen by the European Community to stop climate changes and environmental degradation, and to enable a sustainable growth. For this purpose, the construction of a new and more dynamic electricity distribution network is mandatory. This “smart grid” should also include small and medium-size companies, able to program the generation and use of energy from renewable sources (the so-called "prosumers"). In this frame, micro-cogeneration (rated electric power up to 50 kW) is one of the most promising techniques.
In this work, the application to micro-cogeneration of an innovative Compression Ignition internal combustion engine, operated in Dual Fuel mode is proposed. Thanks to the specific combustion system (Reactivity Controlled Compression Ignition, RCCI: a lean homogenous mixture of air and biomethane or biogas is ignited by the injection of a small amount of Diesel fuel), brake thermal efficiency can be increased at all operating conditions, compared to a conventional Spark Ignition engine running on biomethane or biogas. The ensuing reduction of CO2 emissions is higher than 20%. Furthermore, the proposed engine can tolerate larger variations in the composition of the biogas, without a significant drop of thermal efficiency. Finally, in case of emergency, it is able to run on Diesel fuel only.
The use of the engine is particularly suitable for a company operating in the agricultural field, such as a mid-size farm, that is able to produce biogas for its self-consumption. Therefore, a representative study case is selected, and the corresponding electrical and thermal energy needs are analysed throughout a typical year. The energetic analysis leads to the identification of the most suitable engine size and calibration settings, in order to reduce the purchase of electricity and natural gas, maximizing the use of the company's own renewable sources (biogas or biomethane). The final goal of the optimization process is to create a virtuous system, that can reduce the environmental impact and make the company almost independent from the energetic point of view.
Dual fuel diesel engines can provide lower emissions as well as allow a diversified fuel supply. Dual fueling of diesel engines is typically accomplished using a gaseous fuel in the intake manifold and a quantity of pilot diesel directly injected into the cylinder to initiate combustion. However low load dual fuelling typically leads to a higher unburnt hydrocarbon component. Large engines for heavy machinery and marine applications will continue to be required and thus research on their use instigated this research to mitigate the undesirable unburnt hydrocarbon at part load. An electronic throttle body was implemented in the intake of a two-liter common rail diesel engine that had been converted to dual fuel operation. The throttle body was used to reduce the quantity of air admitted into the engine and thus a lower air-to-fuel ratio (i.e. closer to stochiometric). This was achieved with the aim of achieving better combustion in the end gas region and thus lower unburnt hydrocarbons. A low cost MQ8 hydrocarbon sensor was used to measure the unburnt hydrocarbons in the exhaust.
The burning of diesel and compressed natural gas (CNG) is attractive compared to diesel fuel because of the reduction of CO 2 emissions and particulate matter (PM) emissions. While soot emissions from the diesel-CNG combustion can be tested in a real-world single-cylinder engine, the soot formation characteristics cannot be tested in the same way. Therefore, to understand the mechanisms behind soot formation in diesel-CNG combustion, soot evolution must be investigated using a simulation model. In this study, the soot evolution is investigated under different CNG substitution ratios with single and split fuel injection. An AVL 5402 single-cylinder diesel engine was modified to run diesel/CNG dual-fuel to investigate the combustion and soot emissions. A new soot model using KIVA-3V R2 code and integrated with a reduced heptane/methane PAH (polycyclic aromatic hydrocarbons) mechanism was used to simulate soot behavior. For the combustion, the results show that the ignition delay gets extended, the combustion duration gets shorter and the peak pressure can be improved when CNG substitution ratio is increased both with single and split injection. Additionally, a slight increase of pressure is observed when the split injection is used. This is because the split injection is an effective strategy to change the distribution and vaporization of fuel, which results in an incremental increase in combustion efficiency and increase pressure. As the CNG substitution ratio is increased, soot emissions get drastically reduced. The reason is the equivalence ratio distribution of air-fuel becomes more homogenous and the local fuel-rich region shrinks with increasing of CNG substitution ratios. Pyrene is an important intermediate specie to generate soot particles. The results show that pyrene distribution decreases, leading to a reduced generation of soot precursors. As a result, the soot mass of CNG70 is less than the other two cases. The basic reason is the prolonged ignition delay allowed for more time for fuel−air mixing, which reduces soot mass formation.
As an inexpensive and low carbon fuel, the combustion of natural gas reduces fuel cost and generates less carbon dioxide emissions than diesel and gasoline. Natural gas is also a clean fuel that generates less particulate matter emissions than diesel during combustion. Replacing diesel by natural gas in internal combustion engines is of great interest for industries. Dual fuel combustion is an efficient way to apply natural gas in internal combustion engines.
An issue that to a certain extent offsets the advantage of lower carbon dioxide emissions in natural gas–diesel dual fuel engines is the higher methane emissions and low engine efficiency at low load conditions. In order to seek strategies to improve the performance of dual fuel engines at low load conditions, an experimental investigation was conducted to investigate the effect of diesel injection split on combustion and emissions performance of a heavy duty natural gas–diesel dual fuel engine at a low load. The operating conditions, such as engine speed, load, intake temperature and pressure, were well controlled during the experiment. The effects of diesel injection split ratio and timings were investigated. The engine efficiency and emissions data, including particulate matter, nitric oxides, carbon monoxide and methane were measured and analyzed. The results show that diesel injection split significantly reduced the peak pressure rise rate. As a result, diesel injection split enabled the engine to operate at a more optimal condition at which engine efficiency and methane emissions could be significantly improved compared to single diesel injection.
The lean-burn capability of the Diesel-ignited gas engine combined with its potential for high efficiency and low CO 2 emissions makes this engine concept one of the most promising alternative fuel converters for passenger cars. Instead of using a spark plug, the ignition relies on the compression-ignited Diesel fuel providing ignition centers for the homogeneous air-gas mixture. In this study the amount of Diesel is reduced to the minimum amount required for the desired ignition. The low-load operation of such an engine is known to be challenging, as hydrocarbon (HC) emissions rise. The objective of this study is to develop optimal low-load operation strategies for the input variables equivalence ratio and exhaust gas recirculation (EGR) rate. A physical engine model helps to investigate three important limitations, namely maximum acceptable HC emissions, minimal CO 2 reduction, and minimal exhaust gas temperature. An important finding is the fact that the high HC emissions under low-load and lean conditions are a consequence of the inability to raise the gas equivalence ratio resulting in a poor flame propagation. The simulations on the various low-load strategies reveal the conflicting demand of lean combustion with low CO 2 emissions and stoichiometric operation with low HC emissions, as well as the minimal feasible dual-fuel load of 3.2 bar brake mean effective pressure.
Research on the combustion and performance of dual fuel stationary engines using natural gas and methane is found to be adequate in published literature. The emissions aspects, however, are less well investigated. Inadequacy is also noted in the case of published research works on biogas in dual fuel engines in respect of regulated emissions. One important pollutant which has not received much attention among researchers is the particulate matter (PM) for such applications. Though it is often claimed that PM emissions from gas-diesel dual fuel engines are much reduced, few works have been published to support this claim. The present study is intended to help fill the gap and all the regulated emissions (CO, CO2, NOx, UHC) including PM are measured for a Lister Petter direct injection stationary diesel engine modified for dual fuel applications. Two alternative gaseous fuels used in this study are natural gas and biogas. PM is measured by the conventional gravimetric method and PM physical structures are observed visually and are analyzed by scanning electron microscopy. Results are compared between the diesel and dual fuel operations and also between natural gas and biogas fueling for a particular engine operating condition. PM emission for dual fueling is found to be reduced by about 70% (on a mass basis) compared to diesel fueling at the same operating conditions. Also smaller and rounder particulate agglomerates are observed and measured for dual fueling as compared to diesel fueling.
Nowadays, the most critical issues concerning internal combustion engines are the reduction of the pollutant emissions, in particular of CO2, and the replacement of fossil fuels with renewable sources. An interesting proposition for Diesel engines is the Dual Fuel (DF) combustion, consisting in the ignition of a premixed charge of gaseous fuel (typically natural gas) by means of a pilot injection of Diesel Fuel. Dual fuel combustion is a quite complex process to model, since it includes the injection of liquid fuel, superimposed with a premixed combustion. However, CFD simulation is fundamental to address a number of practical issues, such as the setting of the liquid injection parameters and of the gaseous fuel metering, as well as to get the maximum benefit from the DF technique. In this paper, a customized version of the KIVA-3V Computational Fluid Dynamic (CFD) code was adopted to analyze the combustion process of a 4-cylinder, 2.8 1, turbocharged HSDI Diesel engine, operating in both Diesel and DF (Diesel and Natural Gas) modes. Starting from a previously validated diesel combustion model, a natural gas combustion model was implemented and added to simulate the DF operations. Available engine test data were used for validation of the diesel-only operation regimes. Using the calibrated model, the influence of the premixed charge composition was investigated, along with the effect of the diesel injection advance angle, at a few characteristic operating conditions. An optimum setting was eventually found, allowing the DF engine to deliver the same brake power of the original Diesel unit, yielding the same maximum in-cylinder pressure. It was found that DF combustion is soot-less, yields a strong reduction of CO and CO2, but also an increase of NO.
This article covers key and representative developments in the area of high efficiency and clean internal combustion engines. The main objective is to highlight recent efforts to improve (IC) engine fuel efficiency and combustion. Rising fuel prices and stringent emission mandates have demanded cleaner combustion and increased fuel efficiency from the IC engine. This need for increased efficiency has placed compression ignition (CI) engines in the forefront compared to spark ignition (SI) engines. However, the relatively high emission of oxides of nitrogen (NOx) and particulate matter (PM) emitted by diesel engines increases their cost and raises environmental barriers that have prevented their widespread use in certain markets. The desire to increase IC engine fuel efficiency while simultaneously meeting emissions mandates has thus motivated considerable research. This paper describes recent progress to improve the fuel efficiency of diesel or CI engines through advanced combustion and fuels research. In particular, a dual fuel engine combustion technology called “reactivity controlled compression ignition” (RCCI), which is a variant of Homogeneous Charge Compression Ignition (HCCI), is highlighted, since it provides more efficient control over the combustion process and has the capability to lower fuel use and pollutant emissions. This paper reviews recent RCCI experiments and computational studies performed on light- and heavy-duty engines, and compares results using conventional and alternative fuels (natural gas, ethanol, and biodiesel) with conventional diesel, advanced diesel and HCCI concepts.
Compressed natural gas/Diesel dual-fuel combustion mode, the partial replacement of diesel fuel with cleaner fuel, is one of the most important strategies to achieve clean efficient combustion. Thus, the current work investigated the effect of various natural gas substitution ratios on the combustion and soot emission characteristics experimentally in an optical diesel engine. Experiments were performed at different compressed natural gas (CNG) substitution rates of 30%, 50%, 70%, 85% (based on energy) over a wide range of equivalence ratios of the premixed charge. In-cylinder flame images were captured by a high-speed camera and further processed to obtain flame characteristics as well as soot distributions. The results show that the effect of natural gas is reflected mainly in the premixed flame area and a change of the ignition delay period. As the substitution ratio increasing, the pressure and the heat release rate decrease, while the ignition delay period prolongs and the premixed flame distribution is more extensive. Besides, high-temperature regions and the soot volume fraction decrease, especially at higher substitution ratios conditions. Through controlling the natural gas substitution ratios, an efficient and clean combustion mode for dual-fuel engines can be found. In general, higher natural gas substitution rate leads to cleaner combustion trends and more desirable flame characteristics.
Dual-fuel premixed charge compression ignition (DF-PCCI) combustion can achieve low nitrogen oxides (NO X ) and particulate matter (PM) emissions for wide ranges of engine operations. However, the deterioration in thermal efficiency, and hydrocarbon (HC) and carbon monoxide (CO) emissions at low loads were recognized as the barriers for expanding the low-load operating range. In this study, the causes of the barriers were investigated and a mixture preparation strategy was suggested for overcoming the barriers in a natural gas (NG)-diesel DF-PCCI engine. Combustion and energy balance analysis was conducted to evaluate the strategy. Baseline DF-PCCI was determined by combinations of diesel start of injection (SOI) and NG substitution ratio (SR) at low loads from 0.3 to 0.6 MPa indicated mean effective pressure (IMEP). An increase in the homogeneity of a fuel-air mixture in the baseline DF-PCCI effectively reduced the NO X and PM emissions but increased the HC and CO emissions in each low-load operation. As the engine load was decreased, the formation of an overly-lean mixture intensified the effects of the mixture homogeneity. Therefore, the thermal efficiency, and HC and CO emissions deteriorated at 0.3 MPa IMEP. A mixture stratification strategy was established to increase the local equivalence ratio and reactivity of the fuel-air mixture. The strategy was realized by a retarded diesel SOI, a lower NG SR, and a higher exhaust gas recirculation rate. The strategy increased the degree of constant volume combustion by enhancing the combustion performance. The enhanced combustion reduced the combustion loss, and thus, improved the thermal efficiency. The HC and CO emissions also decreased mainly due to the improved combustion and the reduced mass flow rates of the NG.
Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been demonstrated as a promising solution for simultaneous reduction of nitrogen oxides (NOX) and particulate matter (PM) emissions in heavy-duty compression ignition engines. The use of natural gas (NG) as the low-reactivity fuel in DF-PCCI combustion can expand the limited range of high load operations owing to the lower reactivity of NG than that of gasoline. However, the lower reactivity of NG results in significant hydrocarbon (HC) and carbon monoxide (CO) emissions at the low load operations. In this study, the mixture formations with and without exhaust gas recirculation (EGR) in NG-diesel DF-PCCI combustion were assessed to reduce the HC and CO emissions as well as to improve the fuel economy at low load operations. Diesel injection timing and NG substitution ratio (SR), which is defined as the proportion of energy stored in NG with respect to the total energy amount, were changed to examine the effects of the mixture formation on the DF-PCCI combustion. The NG SR, which was required to maintain the combustion phasing at a constant crank angle degree (CAD), was increased as the diesel injection timing was retarded in the mixture formation without EGR. The introduction of EGR, in addition to the diesel injection timing and the NG SR, contributed to the favorable mixture formation for the low load operations. The NOX and PM emissions were lower than the EURO VI limitations in both the mixture formations with and without EGR. When the EGR rate of 50% was applied, the indicated thermal efficiency (ITE) increased compared to the case without EGR. The increased ITE was due to the improved combustion efficiency, the higher peak heat release rate (HRR), and the shorter combustion duration. The HC and CO emissions also decreased significantly with the EGR.
Past research has shown that advancing diesel injection timing is a promising approach to decrease the unburned methane and greenhouse gas (GHG) emissions of natural gas/diesel dual-fuel engines at lower engine loads. However, this benefit may not persist under medium to high load-low speed conditions. To explore this, the present paper uses experiments and detailed computational fluid dynamic (CFD) modeling to investigate the impacts of diesel injection timing on the combustion and emissions performance of a heavy-duty natural gas/diesel dual-fuel engine under four different engine load-speed conditions. The results showed that advancing diesel injection timing increases the peak pressure, thermal efficiency, and NOx emissions for all examined engine load-speed conditions. Advancing diesel injection timing also significantly decreases the unburned methane and CO2-equivalent (GHG) emissions of the dual-fuel engine under low load-low speed and medium load-high speed conditions. The concentration of OH and CH4 revealed that the central part of the combustion chamber is the main source of the unburned methane emissions under low load-low speed and medium load-high speed conditions, and advancing diesel injection timing significantly improves the combustion of natural gas-air mixture in this region. However, advancing diesel injection timing slightly increases the unburned methane emissions trapped in the crevice volume. However, this slight increase in the unburned methane emissions in the crevice volume is much lower than its significant decrease in the central region of the combustion chamber. At medium to high load-low speed conditions, there is almost no unburned methane in the central part of the combustion chamber, and the crevice region is considered as the main source of unburned methane emissions. As a result, advancing diesel injection timing does not improve the combustion of natural gas-air mixture in the central part of the combustion chamber but slightly increases the unburned methane trapped in the crevice region. This is the main reason that advancing diesel injection timing slightly increases the unburned methane emissions under medium to high load-low speed conditions. Overall, advancing diesel injection timing significantly increases thermal efficiency and decreases the unburned methane and GHG emissions under low load-low speed and medium load-high speed conditions. It improves the thermal efficiency under medium to high load-low speed conditions, but comes at the expense of increased methane and unchanged GHG emissions.
Comparisons between dual-fuel combustion and conventional diesel combustion (CDC) are often performed using different engine hardware setups, exhaust gas recirculation rates, as well as intake and exhaust manifold pressures. These modifications are usually made in order to curb in-cylinder pressure rise rates and meet exhaust emissions targets during the dual-fuel operation. To ensure a fair comparison, an experimental investigation into dual-fuel combustion has been carried out from low to full engine load with the same engine hardware and identical operating conditions to those of the CDC baseline. The experiments were executed on a single cylinder heavy-duty diesel engine at a constant speed of 1200 rpm and various steady-state loads between 0.3 and 2.4 MPa net indicated mean effective pressure (IMEP). Ethanol was port fuel injected while diesel was direct injected using a high pressure common rail injection system. The start of diesel injection was optimised for the maximum net indicated efficiency in both combustion modes. Varied ethanol energy fractions and different diesel injection strategies were required to control the in-cylinder pressure rise rate and achieve highly efficient and clean dual-fuel operation. In terms of performance, dual-fuel combustion attained higher net indicated efficiency than the CDC mode from 0.6 to 2.4 MPa IMEP, with a maximum value of 47.2% at 1.2 MPa IMEP. The comparison also shows the use of ethanol resulted in 26% to 90% lower nitrogen oxides (NOx) emissions than the CDC operation. At the lowest engine load of 0.3 MPa IMEP, the dual-fuel operation led to simultaneous low NOx and soot emissions at the expense of a relatively low net indicated efficiency of 38.9%. In particular, the reduction in NOx emissions introduced by the utilisation of ethanol has the potential to decrease the engine running costs via lower consumption of aqueous urea solution in the selective catalyst reduction system. Moreover, the dual-fuel combustion with a low carbon fuel such as ethanol is an effective means of decreasing the use of fossil fuel and associated greenhouse gas emissions.
Internal combustion engines that run on compressed natural gas with lean-burn combustion instead of stoichiometric combustion have the potential to reach a high overall efficiency. However, the aftertreatment of unburnt methane in the exhaust gas is problematic. Catalytic methane oxidation is drastically impaired in lean conditions, even when the inlet exhaust gas temperature is high. In this study we link this effect to the availability of carbon monoxide in the exhaust gas. In stoichiometric operation, the exhaust gas contains a significant amount of carbon monoxide. The corresponding catalytic oxidation reaction has a low light-off temperature and the released reaction enthalpy heats the active surface of the catalyst. This heat helps to reach the significantly higher light-off temperature of the catalytic methane oxidation reaction. Lean exhaust gas, however, contains little to no carbon monoxide, and the exhaust gas temperature is not sufficient to reach light-off for the methane oxidation in many operating points of the engine. After investigating the effect experimentally, this article introduces a control-oriented model of the effect that is able to correctly predict the methane conversion efficiency under lean operation. Finally, we discuss different operating strategies in terms of energy consumption and discuss the effect of a moving active zone inside the catalyst.
It has been widely reported that natural gas dual-fuel combustion (DFC) can achieve much lower soot emissions in contrast to conventional diesel combustion (CDC). Thus, using low-pressure direct injection (LPDI) systems could be an alternative for current high-pressure common rail injection systems, which would significantly reduce the system cost. The present study aimed at exploring the feasibility of LPDI (low to 200 bar) for natural gas DFC in combination of the advanced low temperature combustion technology. The comparative study between natural gas DFC and CDC were carried out. For natural gas DFC, larger advanced injection timing was used to realize low temperature combustion and achieve long ignition delay in order to counteract the negative impact of relatively poor atomization quality caused by the low injection pressure. At DFC mode, higher CO and THC emissions were observed compared to CDC in the cases without EGR. However, DFC was much less sensitive to EGR rate and injection pressure. Natural gas DFC could break the trade-off between NOx and soot emissions, which could achieve low soot and NOx emissions (lower than Europe VI standard: 0.4 g/kW·h) simultaneously at the 42% EGR rate and the 200 bar injection pressure.
Natural gas/diesel dual-fuel combustion is currently one of the most promising LTC strategies for the next generation of heavy-duty engines. While this concept is not new and it has been deliberated lengthily in the past two decades, several uncertainties still exist. A major shortcoming of this concept is associated with its low thermal efficiency and high level of unburned methane and CO emissions under low engine load conditions. The present paper reports an experimental and numerical study on the effect of different injection strategies (single and two pulses injection of pilot diesel fuel) on the combustion performance and emissions of a heavy duty natural gas/diesel dual-fuel engine at 25% engine load. The results of single diesel injection mode showed that advancing diesel injection timing from 10 to 30 °BTDC reduced unburned methane and CO emissions by 62% and 61% and increased thermal efficiency by 6%; however, NOx emissions increased by 74%. In order to achieve NOx – CH4 and NOx – CO trade-off and increased thermal efficiency at low load conditions, the effect of split injection strategy was experimentally and numerically examined. The results of split injection mode revealed that split injection strategy considerably increases the in-cylinder peak pressure compared to that of single injection (10 °BTDC). The results showed also that the heat release produced by the first injection of diesel fuel considerably increased the in-cylinder charge temperature before the start of the second injection. The flame zone of the split injection mode is markedly higher than that of the single injection due to larger heat release produced during the first injection which promotes the combustion of the second one. When the first injection timing is close to the second injection timing, the MPRR of split injection mode is higher than that of single injection (10 °BTDC). However, further advancing of the first injection timing continuously decreased the MPRR. OH radical analysis showed that for advanced first injection timings (38-50 °BTDC), the overall growth rate of OH radical becomes slower and its distribution is narrower as indicated by the wider non-reactive blue zones compared with those observed at a late first injection timing in the initial stages of combustion. However, OH radicals gradually grow during last stages of combustion in the expansion stroke, indicating that a more premixed combustion takes place in these cases. For very advanced first injection timing of 55 °BTDC, the OH distribution is similar to that of the single injection mode with lower OH intensity at initial stages of combustion and they barely grow during the late expansion stroke. At this condition, the ignition of premixed mixture is mainly controlled by the second diesel fuel injection. The trade-off between NOx – CH4 and NOx – CO is achieved when applying split injection. Compared to single injection (10 °BTDC), the first injection timing of 50 °BTDC decreased unburned methane and CO emissions by 60% and 63%, respectively, and increased the thermal efficiency by 8.9%. However, NOx emissions were maintained at the same level as single injection mode (10 °BTDC).
The present study deals with the simulation of a Diesel engine fuelled
by natural gas/diesel in dual fuel mode to optimize the engine
behaviour in terms of performance and emissions. In dual fuel mode,
the natural gas is introduced into the engine’s intake system. Near the
end of the compression stroke, diesel fuel is injected and ignites,
causing the natural gas to burn. The engine itself is virtually
unaltered, but for the addition of a gas injection system. The CO2
emissions are considerably reduced because of the lower carbon
content of the fuel. Furthermore, potential advantages of dual-fuel
engines include diesel-like efficiency and brake mean effective
pressure with much lower emissions of oxides of nitrogen and
particulate matter. In previous papers, the authors have presented
some CFD results obtained by two 3D codes by varying the diesel/
NG ratio and the diesel pilot injection timing at different loads. The
calculations have been referred to a light duty direct injection diesel
engine, of which some experimental data were available, obtained
both in full diesel and Dual Fuel operating conditions. These data
have allowed to realize a fitting of the models. The phenomena
involved in the cylinder are very complex and the numerical results
obtained demonstrate a strong dependence on the boundary
conditions imposed at the cylinder control system, provided by
experimental data. Therefore, a comprehensive simulation of all
engine should be necessary, by testing numerous operating
conditions. In fact, the reduced experimental test cases available do
not allow an overall view of the engine behaviour in the different
operating conditions and cannot provide appreciable inlet conditions
in cylinder for 3D combustion calculations. At the same time, the 3D
results can define some inputs (turbulence, combustion law, etc.) for
the one-dimensional simulation of the entire system fora preliminary
calibration of some engine parameters. In particular, the calculations
have been made by using an advanced 1D engine cycle simulation
software enable to carry out performance simulations based on
virtually any intake, combustion, exhaust system and turbocharger
design, at different operating conditions, by varying large number of
parameters. Thecode is based on one-dimensional flow through ducts and zero-dimensional in-cylinder calculation. Detailed modelling of
individual components is included to specify the phenomena in the
singular components.
Diesel engines find widespread applications in stationary and transportation systems owing to their high fuel efficiency, high torque output, and great size flexibility. However, they still constitute major polluting sources, especially regarding NO and particulate emissions. Therefore, more conventional diesel engines internationally are pursuing the option of conversion to using natural gas as a supplement fuel for the conventional diesel fuel. Many research studies carried out in the aforementioned research field have shown that the specific engine operating mode, in comparison to the conventional diesel one, suffers from higher specific fuel consumption and CO emission. The diesel fuel injection timing and the proportion of the gaseous fuel influence significantly the combustion mechanism, with this effect becoming more evident at part load conditions. Thus, in order to examine the effect of these two parameters on the performance and exhaust emissions, a combined experimental and theoretical investigation is conducted herein on a single-cylinder research, dual fuel (diesel-natural gas), HDDI compression ignition engine. Specifically, through the experimental investigation the effect of diesel fuel injection timing is examined on the performance and exhaust emissions of the engine operating under part load and constant natural gas/diesel mass ratio conditions. Moreover, following validation of the latter, theoretical results concerning the combined effects of both parameters of diesel fuel injection timing and natural gas/diesel mass ratio on the performance and exhaust emissions characteristics of the engine operating at two different loading conditions are obtained, via the application of an in-house, comprehensive, two-zone phenomenological model. The main objective of this assessment is to record and comparatively evaluate the relative impact of these parameters for part and high engine loading conditions. From the experimental and theoretical findings, it is revealed that for the examined test engine operating under constant natural gas/diesel mass ratio, a restricted increase in the diesel fuel injection timing could be a promising solution for engine efficiency improvement and CO emission mitigation, while simultaneously it seemed to increase NO emissions. For extremely advanced diesel fuel injection timing, a simultaneous variation of natural gas/diesel mass ratio at both engine loading conditions could cause problems to the engine structure because, in those cases, the maximum cylinder pressure becomes considerable and hence possibly harmful to the engine structural integrity. The information derived from the present work is valuable, especially if one wishes to define the optimum combination of examined strategies for improving the behavior of an existing engine running under natural gas/diesel operating mode.
Natural gas/diesel dual-fuel combustion compression ignition engine has the potential to reduce NOx and soot emissions. However, this combustion mode still suffers from low thermal efficiency and high level of unburned methane and CO emissions at low load conditions. The present paper reports the results of an experimental and numerical study on the effect of diesel injection timings (ranging from 10 to 50 °BTDC) on the combustion performance and emissions of a heavy duty natural gas/diesel dual-fuel engine at 25% engine load. Both experimental and numerical results revealed that advancing the injection timing up to 30 °BTDC increases the maximum in-cylinder pressure. However, with further advancing the injection timing up to 50 °BTDC, the maximum in-cylinder pressure decreases which is mainly due to the lower in-cylinder temperature before SOC. Moreover, the analysis of OH spatial distribution shows that, at very advanced diesel injection timings, the non-reactive zones are much narrower than later injection timings during the last stages of combustion, indicating a more predominant premixed combustion mode. At retarded diesel injection timings, the consumption of premixed fuel in the outer part of the charge is likely to be a significant challenge for dual-fuel combustion engine at low engine load conditions. However, with advancing the diesel injection timing, the OH radical becomes more uniform throughout the combustion chamber, which confirms that high temperature combustion reactions can occur in the central part of the charge. Diesel injection timing of 30 °BTDC appears to be the conversion point of all conventional dual-fuel combustion modes. Further advancing diesel injection timing beyond this point (30 °BTDC) results in noticeable reduction in NOx and unburned methane emissions, while CO emissions exhibit only slight drop. However, at very advanced diesel injection timings of 46 and 50 °BTDC, NOx, and unburned methane emissions continue to drop, whereas and CO emissions tend to increase. The results showed also that the highest indicated thermal efficiency is achieved at these very advanced diesel injection timings of 46 and 50 °BTDC. Finally, the results revealed that, by advancing diesel injection timing from 10 °BTDC to 50 °BTDC, NOx, unburned methane, and CO emissions are reduced, respectively, by 65.8%, 83%, and 60% while thermal efficiency is increased by 7.5%.
This experimental work investigates the capabilities of the reactivity controlled compression ignition combustion concept to be operated in the whole engine map and discusses its benefits when compared to conventional diesel combustion. The experiments were conducted using a single-cylinder medium duty diesel engine fueled with regular gasoline and diesel fuels. The main modification on the stock engine architecture was the addition of a port fuel injector in the intake manifold. In addition, with the aim of extending the reactivity controlled compression ignition operating range towards higher loads, the piston bowl volume was increased to reduce the compression ratio of the engine from 17.5:1 (stock) down to 15.3:1. To allow the dual-fuel operation over the whole engine map without exceeding the mechanical limitations of the engine, an optimized dual-fuel combustion strategy is proposed in this research. The combustion strategy changes as the engine load increases, starting from a fully premixed reactivity controlled compression ignition combustion up to around 8 bar IMEP, then switching to a highly premixed reactivity controlled compression ignition combustion up to 15 bar IMEP, and finally moving to a mainly diffusive dual-fuel combustion to reach the full load operation. The engine mapping results obtained using this combustion strategy show that reactivity controlled compression ignition combustion allows fulfilling the EURO VI NOx limit up to 14 bar IMEP. Ultra-low soot emissions are also achieved when the fully premixed combustion is promoted, however, the soot levels rise notably as the combustion strategy moves to a less premixed pattern. Finally, the direct comparison of reactivity controlled compression ignition versus conventional diesel combustion using the nominal engine settings, reveals that reactivity controlled compression ignition can be a potential solution to reduce the selective catalyst reduction and diesel particulate filter aftertreatment necessities with a simultaneous improving of the thermal efficiency.
Natural Gas (NG) is currently a cost effective substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. Dual-Fuel engines substitute NG in place of diesel for decreased NOx and soot
emissions, but suffer from high engine-out methane (CH4) emissions. Premixed Dual-Fuel Combustion (PDFC) is one method of decreasing methane emissions and simultaneously improving engine efficiency while maintaining low NOx and soot levels. PDFC utilizes an early diesel injection to adjust the flammability of the premixed charge, promoting more uniform burning of methane. Engine experiments were carried out using a NG and diesel HD single cylinder research engine. Key speeds and loads were explored in order to determine where PDFC is effective at reducing engine-out methane emissions over Conventional Dual-Fuel which uses a single diesel injection for ignition. PDFC has shown significant reductions in methane as well as CO emissions when compared with Conventional Dual-Fuel combustion. Medium loads enjoy the largest benefit from PDFC. At higher load, the amount of diesel injected early was limited in order to stay within the constraints for cylinder pressure. At lighter loads, the benefits of PDFC are reduced due to higher in-cylinder global lambda (λ) and lower temperature and pressure to promote auto-ignition. Overall, the PDFC mode of operation observes the potential to minimize the need for exhaust after-treatment as well as increase engine efficiency.
Piston bowl geometries are crucial to the combustion and emission characteristics of reactivity controlled compression ignition (RCCI) engines. The present numerical study explores the effects of piston bowl geometry on natural gas/diesel RCCI performance and emissions at medium engine load. Three different piston bowl geometries including stock, bathtub and cylindrical with constant compression ratio 16.1:1 are selected using double injection strategy and Influences of engine speed, piston bowl depth and chamfered ring-land are investigated. It is found that the bowl profile does not affect combustion of RCCI engine at low engine speeds, but it has much considerable effect at higher engine speeds. The results obtained also show that bathtub design yields the best performance and emissions at higher speeds. It is also reported that both piston bowl depth and chamfered ring-land can also affect engine-out emissions specially UHC and CO emissions.
The brake thermal efficiency and exhaust emission issues are still not fully-resolved to diesel/natural gas dual fuel engines. To better understand the effect of pilot diesel ignition mode on combustion and emissions characteristics of dual fuel engines, a detailed study concerned with diesel injection timing was conducted. The testing work was operated on a 6-cylinder turbocharged intercooler diesel/natural gas dual fuel heavy-duty engine at light load operations, and diesel injection timing was controlled over a very wide range. The investigated results show that the diesel injection timing (Tinj) has an obvious effect on pilot diesel ignition mode. A significant advancing Tinj leads to pilot diesel ignition mode differs from traditional diesel engine compression ignition mode in the sense that it does not occur at a specific place in the spray, which is a two-stage autoignition mode. With advancing Tinj, engine combustion and emissions characteristics, including cylinder pressure, cylinder temperature, heat release rate, start of combustion (SOC), ignition delay, combustion duration, crank angle of 50% heat release (CA50), nitrogen oxides (NOx) and total hydrocarbon (THC), show completely different variation trends in different ignition modes. Overall, higher thermal efficiency and lower emissions can be achieved simultaneously in two-stage autoignition mode. Satisfactory results can be obtained with higher brake thermal efficiency (35%), lower NOx (60 ppm) and THC (0.4%) emissions, when Tinj is 42.5 °CA BTDC.
Many recent studies have shown that the Reactivity Controlled Compression Ignition (RCCI) combustion strategy can achieve high efficiency with low emissions. However, it has also been revealed that RCCI combustion is difficult at high loads due to its premixed nature. To operate at moderate to high loads with gasoline/diesel dual fuel, high amounts of EGR or an ultra low compression ratio have shown to be required. Considering that both of these approaches inherently lower thermodynamic efficiency, in this study natural gas was utilized as a replacement for gasoline as the low-reactivity fuel. Due to the lower reactivity (i.e., higher octane number) of natural gas compared to gasoline, it was hypothesized to be a better fuel for RCCI combustion, in which a large reactivity gradient between the two fuels is beneficial in controlling the maximum pressure rise rate. The multi-dimensional CFD code, KIVA3V, was used in conjunction with the CHEMKIN chemistry tool and a Nondominated Sorting Genetic Algorithm (NSGA-II) to perform optimization for a wide range of engine operating conditions. Engine design parameters that were controlled by the genetic algorithm include the fraction of total fuel that is premixed (methane), the timing of the two diesel injections, the amount of diesel in each injection, the diesel fuel injection pressure, and the EGR percentage. The objective of the optimization was to simultaneously minimize soot, NOx, CO, and UHC emissions, as well as ISFC and ringing intensity. A broad load/speed range was investigated; six operating points from 4 to 23 bar IMEP and 800 to 1800 rev/min were optimized. These load/speed combinations represent typical heavy-duty engine conditions. Using the stock compression ratio of 16.1, it was determined that operation up to 13.5 bar IMEP could be achieved with no EGR, while still maintaining high efficiency and low emissions. The study also examined the sensitivity of RCCI combustion at high load to injection system parameters. The results emphasize that precise injection control is needed for combustion control.
In this paper, a common rail diesel research engine was converted to operate in dual-fuel mode and extensive experiments were conducted to investigate the effects of natural gas injection timing on the combustion and emissions performance under different pilot injection pressure and timing at low load conditions. The presented results include the cylinder pressure, heat release rate (HRR), ignition delay, combustion duration and brake thermal efficiency, as well as CO, HC and NOx emissions at different natural gas injection timing under pilot injection pressure (46 and 72 MPa) and pilot injection timing (−8° and −17° ATDC) operation conditions at low load (BMEP = 0.24 MPa). The results indicated that retarded natural gas injection timing can achieve a stratified-like air-fuel mixture in cylinder under the different pilot injection conditions, which provided a method to improve the combustion performance and exhaust emissions at low load. Moreover, under higher pilot injection pressure (72 MPa) conditions, better combustion performance, such as shorter ignition delay and combustion duration, higher brake thermal efficiency, were achieved; however, the exhaust emissions significantly increased compared with those under lower pilot injection pressure (46 MPa). On the other hand, under the advanced pilot injection timing (−17° ATDC), the combustion performance was radically better, THC and CO emissions were lower but the NOx emissions were significantly higher compared with those under the regular pilot injection timing (−8° ATDC). This is attributed to faster flame propagation speed, better combustion phasing and higher volumetric efficiency. Consequently, employing appropriate natural gas injection timing accompanied with reasonable pilot injection parameters is critical to further improve combustion performance and exhaust emissions of a dual-fuel engine at low loads.
The use of natural gas in compression ignition engines as supplement to liquid diesel in a dual fuel combustion mode is a promising technique. In this study, the effect of DF (dual fuel) operating mode on combustion characteristics, engine performances and pollutants emissions of an existing diesel engine using natural gas as primary fuel and neat diesel as pilot fuel, has been examined. At moderate and relatively high loads, the results show very interesting behavior of dual fuel operating mode in comparison to conventional diesel, both for engine performance and emissions. It showed a simultaneous reduction of soot and NOx species over a large engine operating area. Moreover, it showed the possibility to obtain lower BSFC (brake specific fuel consumption) than conventional diesel engine. However, this mode presents some deficits at low loads, especially concerning unburned hydrocarbons and carbon monoxide emissions. Understanding those deficiencies is a key of such engines improvement. Some suggestions for new measures towards DF mode improvement are deduced.
The use of natural gas as a partial supplement for liquid diesel fuel is a very promising solution for reducing pollutant emissions, particularly nitrogen oxides (NOx) and particulate matters (PM), from conventional diesel engines. In most applications of this technique, natural gas is inducted or injected in the intake manifold to mix uniformly with air, and the homogenous natural gas–air mixture is then introduced to the cylinder as a result of the engine suction.This type of engines, referred to as dual-fuel engines, suffers from lower thermal efficiency and higher carbon monoxide (CO) and unburned hydrocarbon (HC) emissions; particularly at part load. The use of exhaust gas recirculation (EGR) is expected to partially resolve these problems and to provide further reduction in NOx emission as well.In the present experimental study, a single-cylinder direct injection (DI) diesel engine has been properly modified to run on dual-fuel mode with natural gas as a main fuel and diesel fuel as a pilot, with the ability to employ variable amounts of EGR. Comparative results are given for various operating modes; conventional diesel mode, dual-fuel mode without EGR, and dual-fuel mode with variable amounts of EGR, at different operating conditions; revealing the effect of utilization of EGR on combustion process and exhaust emission characteristics of a pilot ignited natural gas diesel engine.
Catalytic oxidation of hydrocarbons in lean-burn natural-gas engine exhaust has been studied for Pt and Pd supported on alumina. A Pt–Pd/alumina catalyst exhibited higher and longer-lasting hydrocarbon oxidation activity than Pt–Rh/alumina, Pt/alumina, and Pd/alumina catalysts. Increasing the palladium content in Pt–Pd/alumina catalyst increased the oxidation activity and had more durability. While increasing the platinum content a little bit also improved the activity, adding much more did not. Supporting the platinum on alumina retarded the sintering of Pd and PdO, thus lengthening the oxidation activity of the Pt–Pd/alumina catalyst.
With the increasing concern regarding diesel vehicle emissions and the rising cost of the liquid diesel fuel as well, more conventional diesel engines internationally are pursuing the option of converting to use natural gas as a supplement for the conventional diesel fuel (dual fuel natural gas/diesel engines). The most common natural gas/diesel operating mode is referred to as the pilot ignited natural gas diesel engine (PINGDE) where most of the engine power output is provided by the gaseous fuel while a pilot amount of the liquid diesel fuel injected near the end of the compression stroke is used only as an ignition source of the gaseous fuel–air mixture. The specific engine operating mode, in comparison with conventional diesel fuel operation, suffers from low brake engine efficiency and high carbon monoxide (CO) emissions. In order to be examined the effect of increased air inlet temperature combined with increased pilot fuel quantity on performance and exhaust emissions of a PINGD engine, a theoretical investigation has been conducted by applying a comprehensive two-zone phenomenological model on a high-speed, pilot ignited, natural gas diesel engine located at the authors' laboratory. The main objectives of the present work are to record the variation of the relative impact each one of the above mentioned parameters has on performance and exhaust emissions and also to reveal the advantages and disadvantages each one of the proposed method. It becomes more necessary at high engine load conditions where the simultaneous increase of the specific engine parameters may lead to undesirable results with nitric oxide emissions.
In the effort to reduce pollutant emissions from diesel engines various solutions have been proposed, one of which is the use of natural gas as supplement to liquid diesel fuel, with these engines referred to as fumigated, dual fuel, compression ignition engines. One of the main purposes of using natural gas in dual fuel (liquid and gaseous one) combustion systems is to reduce particulate emissions and nitrogen oxides. Natural gas is a clean burning fuel; it possesses a relatively high auto-ignition temperature, which is a serious advantage over other gaseous fuels since then the compression ratio of most conventional direct injection (DI) diesel engines can be maintained high. In the present work, an experimental investigation has been conducted to examine the effects of the total air–fuel ratio on the efficiency and pollutant emissions of a high speed, compression ignition engine located at the authors’ laboratory, where liquid diesel fuel is partially substituted by natural gas in various proportions, with the natural gas fumigated into the intake air. The experimental results disclose the effect of these parameters on brake thermal efficiency, exhaust gas temperature, nitric oxide, carbon monoxide, unburned hydrocarbons and soot emissions, with the beneficial effect of the presence of natural gas being revealed. Given that the experimental measurements cover a wide range of liquid diesel supplementary ratios without any appearance of knocking phenomena, the belief is strengthened that the findings of the present work can be very valuable if opted to apply this technology on existing DI diesel engines.
KOHLER G2-165 Technical Datasheet
- Kohler Engines
KOHLER Engines, "KOHLER G2-165 Technical Datasheet,"
http://www.kohlerpower.com/onlinecatalog/pdf/g2165.pdf,
accessed July 2020.
Cummins QSB5-G4 Technical Datasheet
- Cummins
Cummins, "Cummins QSB5-G4 Technical Datasheet,"
https://www.cummins.com/g-drive-engines/dieselelectronic-b-series, accessed July 2020.
- G P Mctaggart-Cowan
- S N Rogak
- S R Munshi
- P G Hill
McTaggart-Cowan, G.P., Rogak, S.N., Munshi, S.R., Hill,
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