Range Extended Hybrid Series Vehicles with Gas Turbines for Urban Transportation Systems

Abstract

Environmental pollution in large cities is approximately 20% due to the transportation system. At same time the “vehicle operating life” are most often overcome and the vehicles emissions do not comply the European anti-pollution standards. It becomes mandatory to find a solution that respects the environment and can provide the appropriate service to its customers. New technologies related to hybrid-electric engines are making great strides in reducing emissions. In addition, the implementation of new technologies is convenient also from the economic point of view. In fact, implementing hybrid vehicles, the fuel consumption can be reduced. The hybrid configuration studied in this paper developed at the University of Rome Sapienza, consisting in a Gas Turbine set (GT), powered by natural gas/LPG. The energy produced can be supplied or to the battery package (battery recharging, RANGE EXTENDED operating mode) or directly to the electric motor. The simulations have provided guidance on the optimal configuration. Finally, a preliminary feasibility analysis has been carried out.

Full text

International Conference Proceedings ISTI-2017
Range Extended Hybrid Series Vehicles with Gas Turbines for Urban
Transportation Systems
ROBERTO CAPATA, KLITON BYLYKBASHI
Department of Mechanical and Aerospace Engineering, University of Roma “Sapienza”,
Faculty of Civil and Industrial Engineering, Roma Italy
roberto.capata@uniroma1.it, kliton.bylykbashi@uniroma1.it
Abstract
Environmental pollution in large cities is approximately 20% due to the transportation system. At same time the
“vehicle operating life” are most often overcome and the vehicles emissions do not comply the European anti-
pollution standards. It becomes mandatory to find a solution that respects the environment and can provide the
appropriate service to its customers. New technologies related to hybrid-electric engines are making great strides
in reducing emissions. In addition, the implementation of new technologies is convenient also from the
economic point of view. In fact, implementing hybrid vehicles, the fuel consumption can be reduced. The hybrid
configuration studied in this paper developed at the University of Rome Sapienza, consisting in a Gas Turbine
set (GT), powered by natural gas/LPG. The energy produced can be supplied or to the battery package (battery
recharging, RANGE EXTENDED operating mode) or directly to the electric motor. The simulations have
provided guidance on the optimal configuration. Finally, a preliminary feasibility analysis has been carried out.
Keywords: Series Hybrid, Gas Turbine, Feasibility Analysis, Vehicle Implementation, Components
Packaging, Proposed Solution
1. Introduction
An efficient transport system allows the possibility to reach new markets and strengthen the
existing ones. Consequently, it allows and promotes a strong economic growth, globally
productive and competitive. An inefficient or low efficient system produces an increase in
traffic congestion, economic and social losses, and loss of working hours, productivity
worsening and social relations. World Transportation absorbs 1,975 Mtoe (million tons of oil
equivalent) per year, i.e. 26% of energy consumption. But if the average energy consumption
for transport is 0.32 toe/inhabitant (tons of oil equivalent per capita), consumption vary
considerably from one continent to another: an European citizen consumes 0.88, a North
American an average of about 2.21, an African one 0.07 toe. Now, motorized mobility, as is
practiced in "developed" countries, is becoming increasingly unsustainable. Indiscriminate
use of motorized transport has three main consequences:
It is dangerous. In 2015, the World Health Organization (WHO) has defined the transport
"a first class medical drama" that causes over 3,000 deaths per day and manifests for 90% of
the world poorest countries.
Motorized transport excludes other modes of transport: tolerating with difficulty
pedestrians, cyclists and public transport, forces them to protect themselves (construction of
sidewalks, bike paths, green areas) or to retreat underground (subway).
Motorized transport model space in favor of sparsely populated city, very scattered. The
most obvious example is that of the West Coast American cities (with a population density
lower than 25 people per hectare and a consumption for transport more than 1.5
toe/inhabitant). At the other extreme there are the Asian cities, exemplified by Hong-Kong
(with a density of almost 350 inhabitants per hectare and a consumption of 0.1
toe/inhabitant).
Besides, the greenhouse gas emissions of motorized transport are estimated at 6301 MtCO2,
the 26% of global CO2 emissions. The Transportation System is the biggest polluters in the
world to use more fossil fuel in public and private vehicles. Nowadays, there is a new
momentum in the study and implementation of efficient vehicles, such as electric vehicles,
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International Conference Proceedings ISTI-2017
hybrids and gas. In the medium to long term, global trends will lead to a further increase in
demand for transport, which will exceed the current capacity of existing systems. It can be
remembered, that, the pollution is concentrated mainly in large urban areas, where the high
presence of population and related activities, cause a high concentration and emission in the
air. The system emissions consist of carbon monoxide CO, carbon dioxide CO2, nitrogen
oxide NOx, and other compounds such as lead Pb, benzene C6H6 and particulate matter (PM).
Pollution not only damages the environment, but also damages the human health. For these
reasons, in recent years, the EU, through a series of regulations, has gradually limited
concentrations of harmful pollutants, such as particulate matter, Sulphur dioxide, lead,
nitrogen oxides, carbon monoxide and benzene. Across Europe, these substances are released
by several factors. In detail, for PM10:
1. Transport 36% (2/3 due to wheeled transportation);
2. Industry 26%;
3. Civil industry 17%;
4. Agriculture 11%
As It can be notice, the transports are the main “responsible” of air pollution. Especially in
the large urban areas, where the population density and transportation reached high levels,
causing 70% of total emissions. There is a growing demand for vehicles by the world's
population (2.8% average per year), but fortunately there is no longer a high content of
benzene and lead in fuel. Most of the goods delivery is done by truck (61.5%), 21.7% by rail
and 11.5% by ships.
2. Electric Vehicles (EVs) & Hybrid Vehicles (HVs) definition
A first distinction needed. It should not confuse “traction” with “propulsion”. The traction is
assured by the electric motor, while the propulsion can be electrical or thermal, or by
coupling the two engines. If the electric motor receives the required energy from a battery
package, an all-electric vehicle is considered [2,3]. This vehicle needs recharging stations,
consistent with the operational autonomy of the battery, that affect the range of the vehicle. If
the electric motor is driven by the battery package and by a thermal engine, the vehicle is
called “hybrid”. Actually, this vehicle is a thermal-electric vehicle. Despite the EVs, either
all-electric or hybrid, represent an effective solution for reducing the “local” emissions (city,
extra urban agglomerations). In an electric vehicle, the engine, that supplies power to the
wheels, is an electric motor powered by a battery pack. The battery package is rechargeable
one, and a VMU manages and distributes the energy flows to and from the electric motor.
The electric motor can be an AC or DC one. The DC motor is cheaper and easier to
maintain/build. These motors can also work, for a limited time, on "overdrive" conditions,
absorbing more energy than the rated one. This aspect is very beneficial during acceleration.
The use of the overdrive is limited by the risk of overheating. The AC motor is more
expensive. Actually, the AC motors are the typical three-phase motors and is expected, on the
vehicle, the KERS. This device is able to recover 15% regenerative braking [5]. The last
important aspect is the battery package. Eliminate lead acid batteries, because pollutants,
bulky, heavy, expensive and characterized by an excessive charge time, the researchers
attention has focused on lithium-ion batteries (Li-ion) or nickel (NiMH). However, the cost
of these battery packs is very high. Finally the charging system, necessary for the vehicle
operation. For the all mentioned aspects, the electric vehicle technology is constantly
evolving, answering the continuous and variable market demand. Finally, there are three
possible configurations (in this study, only the series hybrid will be considered): Series,
Parallel and Combined
.
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2.1 Series Hybrid
This technology, also called "range extender", is very similar to that used in diesel-electric
locomotives. In such a vehicle, the ICE is not connected to the wheels but is responsible for
generating the electricity to power the electric motor and recharging the batteries. In some
configurations, heat engine can have both two functions. If a large amount of energy is
required, it is drawn from both the heat engine and the battery package. Because electric
motors are able to operate on a wide range of engine speeds, this allows to remove or
simplify the mechanical transmission device. The ICE efficiency changes with speed control,
so the heat engine rpms, in a series hybrid systems are set to get maximum efficiency (the
engine does not suffer neither acceleration nor deceleration). Thanks to this condition it can
use a heat engine (generator), which has a very narrow operational range, compared to the
common heat engines, with a higher efficiency in that “limited” range. In some prototypes
can be installed small electric motors for each wheel (Electric Motor-wheel). The advantage
of this arrangement is the power delivered to each wheel can be separately controlled and
managed. On the other hand, a complex vehicle management (that has to operate as a
mechanical differential) is required. The drawbacks of series hybrid vehicles are the
efficiency reduction in conditions of high and constant speed (typically on the highway, with
a “constant” speed of 130 km/h). Series Hybrid is the most recommended configuration for
vehicles that require continuous braking and restarts as, buses, city cars, sedans and taxis.
Figure 1. Series Hybrid configuration
3. Hybrid Vehicles: Operative description
The adoption of separate motors (that can be used separately or simultaneously) in hybrid
vehicles offers great flexibility of power management, apart from the operational reliability,
concerning the high currents generated and delivered, the key issue concerns the overall
dimensions and electrical characteristics of battery package. Therefore, only by focusing on
the study of performance and cost of the vehicle, as well as on the cost and the actual battery
life, the market can be stimulated to welcome the introduction of hybrid vehicles. The most
sensitive parameter is the cost, and in the short term, the most interesting solution is thermal-
electric configuration, which ensures the reduction of fuel consumption and emissions, and
preserves the current infrastructures network for refueling, without abrupt disruption of the
existing distribution system, as would be necessary in the case of introduction of pure electric
vehicles. The high technological level reached in electronics makes presumably easy to
complete a control logical unit for managing position signals of pedals, instantaneous power
demand, wheel speed, engines speed, emissions, fuel flow, temperature, pressure, current,
voltage and battery State Of Charge (SOC). The vehicle and the control system shall
exchange so continue information: the processor processes the signals according to an
established schedule ("mission control") and sends commands to the actuators, achieving a
balance between performance, consumption, mechanical problems and driving comfort. The
electronics is thus crucial for a hybrid vehicle. To avoid a complex central control module,
can be convenient to utilize a modular system, which provides for each unit its own
processor, all connected via a bus, for the information exchange and coordination. Usually it
is, namely, the Vehicle Management Unit (VMU). There are currently four possible
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configurations of hybrid propulsion, using different ICEs, or gas turbine, and different
electric motors, AC or DC, synchronous and asynchronous, with different solutions in
relation to the mission for which is primarily designed.
4. Proposed GT Hybrid Series Vehicles
At design time, analyzing the conventional hybrid architecture, basing on design goals
(reducing consumption and pollution, ease of assembly and construction, using commercial
products), hybrid powertrain configuration has been adopted. The urban setting is
characterized by short-term accelerations, decelerations and continuous start and stop. This
situation allows to the use of electric vehicles with braking recovery KERS device. This
innovative configuration, renamed GTHV (Gas Turbine Hybrid Vehicle), has been developed
at the Department of Mechanical Engineering of University of Roma. As previously
explained, this is due to the fact that the gas turbine can achieve greater efficiency, especially
when it operates at fixed point and at maximum efficiency. In addition, the overall device
dimensions and weight are lower than a conventional internal combustion engine. Finally, the
GT (gas turbine) set operates as “RANGE EXTENDER”. Preliminary configuration is shown
in the figures 2 and 3. Referring to the vehicle adopted configuration, the VMU is the
fundamental component. The Vehicle Management Unit is the integrated board that
regulates the energy fluxes between the various components. Its control and management
depends on the vehicle architecture and power requirements. It is possible to select 4
operative conditions [27]:
1. Normal Drive: The energy flow is “one direction flow”, from the battery package to the
electric motor. The gas turbine is off.
2. Traction Power Peaks: The energy flow is “open”. In this case, there is a flow from the
battery package to the electric motor. Besides, also the GT set, if need, can supplies power to
the electric motor.
3. Deceleration: The energy flow is reversed by the electric motor to the battery package.
4. Battery Charging: In the case, when the SOC of the battery package drops below a 40%
threshold level (fixed arbitrary but following the manufacturers suggestions) the GT set is
switched on and recharges the package. The traction is provided by the electric motor,
powered by batteries and/or by the GT set (as well as point 2)
4.1 Definition of the Degree of Hybridization (HD)
The hybridization degree HD is a key parameter in the design of a hybrid vehicle. It provides
which traction system is dominant. It indicates if the vehicle has a marked "tendency"
towards electric propulsion or classical one (due to ICE, for instance).The HD can be defined
with the following formula:
Figure 2. Energy fluxes on GT Hybrid Vehicle Figure 3. Components selection
HD = PGT / (PGT + PBP) (1)
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where PGT is the gas turbine rated power, while Pbatt is the battery package power. Adopting a
low HD, the dominant traction system will be the electric one. Moreover, considering the
available commercial gas turbine, the GT set rated power becomes an additional design
constraint. Consequently, several possible configurations have been studied. Last
considerations. A high HD corresponds to a high installed GT power. The system
performance increases, but increase polluting emissions and consumption. These
considerations leads to secure another additional constraint. The maximum value for the HD
is selected equal or lower to 0.5.
Table 1. Considered configuration and HD
Sedan City Car
HD PGT Pbatt HD PGT Pbatt
0.3 30 70 0.4 30 50
0.46 60 70 0.54 60 50
In the design, the Pbatt is set equal to the required power at wheel.
4.2 Selection of the optimal configuration
These simulations have been carried out using a customer code (internally developed called
Lethe) and using commercial tools (Advisor@). Once the vehicle typical physical
characteristics are known, the simulation is carried out. Each vehicle configuration is
identified by its specific parameters set, representing its “attributes.” Several representative
missions (e.g., urban routes for a city car, urban + extra urban for passenger sedan) were
selected for the simulations. The numerical simulations provide, for each type of vehicle and
each type of mission, instantaneous values of the overall vehicle energy demand, of the
energy recovered by the KERS, the energy supplied by the thermal engine and the battery
SOC. The first step in the hybrid powertrain components design is the definition of the
needed driving force. This force is the thrust that the vehicle must generate to move. This
force is higher (at last equal) to the sum of all the resistance forces. These forces depend on
various factors and can be summarized in four general formulae [28].
1. Rolling Resistance. This is the resistance that includes the forces acting on the wheel
during rolling. It is opposite to the circumferential force Fu parallel to the road surface as
shown in figure 8. It is possible to define a rolling resistance coefficient CR
CR = e/rdyn (2)
The resistant force GR is obtained as decomposition of the reaction to the weight force R with
respect to the road inclination. Finally
RT = m∙g∙CR ∙cos

st (3)
2. Aerodynamic resistance. This is the resistance due to the air flow around and through the
vehicle in motion. The aerodynamic drag is proportional to the square of the flow rate,
obtained as the sum of the vehicle speed and the longitudinal component of the wind speed.
This last part is often negligible. Multiplying the square of the speed for the air density air
and dividing by two, the dynamic pressure is so obtained. This pressure multiplied by the
vehicle frontal area AF and by the drag coefficient CD supplies the RA.
RA = ½∙

air ∙CD ∙AF ∙V2m (4)
3. Inertial Resistance. This is the resistance due to the inertial forces during acceleration and
braking. Its value depends directly on the acceleration and the vehicle mass, including the
rotating parts. To consider the rotating inertias, this resistance is multiplied by a
proportionality coefficient, Ci, called rotational inertia coefficient. The inertial resistance can
then express by the following formula:
Ri = m∙a∙Ci(5)
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4. Gradient Resistance. This is the resistance due to the road slope. It is defined as the
product of the weight force for the sine of the road inclination (see figure 8). For flat straight
path, this resistance is zero.
Rg = m∙g∙sin

st (6)
In the simulation, the instantaneous balance equation becomes:
Pwheels = RTOT ∙

∙r = 0 (7)
The simulation code calculates equation (7) at 1-s interval for the entire duration of an
assigned mission. The calculation is repeated for different values of the GT nominal power
rating. The result is a diagram that displays the instantaneous values of each term in the
energy balance as function of time for the selected values of the installed GT power. By
repeating this calculation for a predetermined set of missions, it is possible to select the
battery package modules and the GT set. The codes calculate for any assigned mission and
vehicle configuration, second by second, the power required for traction, the total recoverable
from braking and that available to the KERS. The procedure evaluates the power needed for
acceleration, inertia, rolling resistance and aerodynamic resistance and that recoverable from
deceleration. This operation is repeated for every different vehicle configuration and for all
selected missions. Moreover, the calculation software simulates the vehicle behavior,
calculating fuel consumption and emissions [19].
4.3 Simulation Details and Driving Cycles and Vehicle Characteristics
With the different components and the logic described above, the battery package installed
energy, the GT groups rated power, the fuel consumption and emission for the proposed
passenger sedan, city car have been calculated. In the simulation codes the all above
parameters are used to study the chosen configuration, and indicate, firstly, the “quasi-
optimal” logic to adopt, and then, to supply a preliminary design of the interesting
components, as well as the GT group, the battery package, the flywheel, if any, and the
electric motor. To be able to simulate the different vehicles and choose their optimal
configuration, some information are required. First of all, the vehicle type, i.e., its
aerodynamic characteristics and dimensions. Then it is necessary to know/select the mission
specifications. Several types of missions were simulated, the European and US driving cycles
for approval and homologation (ECE, EUDC, OCC, UDDS, SC03), and other available
(WVU). The aim is to identify the optimal components size and characteristics, to meet the
mission requirements.
Table 2. Vehicles specifications
City CAR Specifications SEDAN CAR Specifications
Rolling radius r = 0.25 m Rolling radius r = 0.25 m
Shape coefficient f = 0.82 Shape coefficient f = 0.9
Actual frontal section Sf = 1.152 m2Actual frontal section Sf = 2.142 m2
Drag coefficient cx = 0.27 Drag coefficient cx = 0.25
Rolling coefficient f = 0.015 Rolling coefficient f = 0.015
Vehicle mass m = 980 kg Vehicle mass m = 1200 kg
Equivalent vehicle mass me = 1210 kg Equivalent vehicle mass me = 1240 kg
Gravity g = 9.81 m/s2Gravity g = 9.81 m/s2
Air density = 1.180 kg/m3Air density  = 1.180 kg/m3
Minimum SOC 0.4 Minimum SOC 0.6 (safety 0.4)
Maximum SOC 0.8 Maximum SOC 0.8
Notice that the BRL does not exceed 2C here. Higher values can be obtained only at the
expenses of the battery package MTBF. The optimal configuration results from a comparison
of all configurations that ensure the instantaneous coverage of the total vehicle demand
power at times “t”.
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4.3.1 The Gas Turbine Fuel Consumption calculation in the simulation
Using data interpolation of a gas turbine performance under Off-Design operating range
[2,7,8,25], varying between 70% and 110% of its rated power, it is possible to get a function
that links the performance variation to the power variation:
ηOD
ηnom
=−1,333 .
(
PGT
Pnom
)
4
+2,497.
(
PGT
Pnom
)
3
−1,768.
(
PGT
Pnom
)
2
+1,646. PGT
Pnom
−0,077
(8)
The methane (CH4) is the adopted fuel, characterized by a lower heating value LHV(CH4) =
51000 kJ/kg = 14.16 kWh/kg and density δCH4 = 0.585 kg/l. From the study of the
thermodynamic cycle and considering a GT efficiency GT = 0.4, it gets a specific
consumption. With these data, the vehicle fuel consumption for a given mission is calculated
as follows. So:
cs,nom = 1/

cycle LHV [kg/kWh] (9)
With these data the vehicle fuel consumption for a given mission is so calculated:
Specific consumption (Off-Design) [kg/kWh]
cs,OD = cs,nom ·

nom/

OD (10)
Instant ct consumption [kg/s]
ct = cs,OD · PGT/3600 where PGT = PGEN/

GEN (ηGEN = 0.95) (11)
Total Consumption [kg/mission]
ctot = ∫mission ct(12)
or in discrete form
ctot = ∑mission ct (13)
Total Consumption [kg/km]
ctot[kg/km] = ctot [kg/mission]/kmtot (14)
Total Consumption [km/l]
ctot[km/l] =

CH4/ctot [kg/mission] (15)
Total specific consumption [g/kWh]
cs,tot[g/kWh] = (3.6 ∙106 ctot [kg/mission])/ ∫Ecycle (16)
with ∫Ecycle = total energy needed to complete the mission
4.4 Simulations results
The simulations were carried out using two codes, a shareware and a costumer one. The
reason for this is dual. First, the costumer code has been validated. The second reason is the
increased data to compare. The code ADVISOR (Advanced Vehicle Simulator) is a software
that simulates the car performance (see figure 4) on an imposed driving cycle, calculating
fuel consumption and emissions [27]. The outputs, provided by the program, are variable and
depend on the simulated car type and on the boundary conditions. The program is based on a
Matlab/Simulink environment. The costumer code (LETHE) is C++ simulation code. In the
program database various driving cycles are considered, for every type of car or vehicle. The
program then does follow the path to the selected car, point by point, generating the required
outputs. The Lethe provides the same graphs. The structure is slightly different. It is based on
equality to zero between the energy required by the wheels (for traction) and the energy
supplied by the system. The inputs are the aerodynamic and operating characteristics of the
vehicle, path performed and the degree of hybridization. The program eventually provides
guidance only on the configuration to adopt to achieve the driving cycles. The emissions
calculation is carried out using a commercial code.
4.4.1 Passanger Sedan
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International Conference Proceedings ISTI-2017
In all simulations, the 70 kWh vehicle battery package is considered. The different GT set are
used to evaluate the vehicle performance. All possible cycles are studied. The “worst case” is
constituted by the 12 EUDC cycles. The SOC level drops below the safety value of 0.4 after
85 min of total mission time. Both sets are able to accomplish the mission. In the case of 30
kW, this set is switched on for a longer time. The evaluation of the use of the two different
sets will have to be made on the basis of economic considerations and series production.
Here follow (figure 6) the results: SOC trend during mission and the GT operating time,
during the mission.
4.4.2 City Car
Two degrees of hybridization has been considered. Both the configuration (first configuration
with a HD = 0.3 and P = 30kW; the second one with HD = 0.4 and P = 60kW) were
successful to recharge the battery package up to the imposed limit. In this case, the
configuration with HD = 0.4 has been discarded. The city car satisfactory performs the
driving cycles adopted, validating the design implemented. In fact, the vehicle manages to
drive about 75 km in pure electric mode. Once the turbo-generator is switched on, further 45
km are needed for charging the battery package. Consumption are in line with those
calculated analytically, while emissions are largely within the Euro 6 limits. It should be
remembered that in the case of methane consumption, the value is intended as m3/100 km.
Figure 4. Advisor@ screen shots Figure 5. Costumer code Screen shots; a) SOC;
b) Energy balance; c) Auxiliary energy storage Energy
balance (if any)
Figure 6. Passenger sedan results Figure 7. City car simulations results
5. Implementing Range Extended Hybrid Series Vehicles and Components Packaging
Once all three vehicles have been simulated, the subsequent design step covered the
“Component Packaging”. For each vehicle, the available frames were implemented in
commercial codes, capable of studying the behavior of the vehicle and its balancing. Several
different versions of the vehicles were studied, keeping the previous drive (front-wheel drive
or rear wheel drive).In addition, was investigated a version, where all vehicles are equipped
with electric motors in the wheels. Besides, since a GT mounted on an axis parallel to the
longitudinal x axis of the vehicle induces rolling; on the y axis, pitching; and on the z axis,
yawing, [9, 13], all rotating parts are placed with a rotation axis parallel to the wheel axis y,
so that roll and yaw are absent and the resulting pitch can be countered by appropriate
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balancing of the suspensions. The components arrangement is to ensure, or try to have, that
the center of gravity passes through the centerline of the vehicle plane. The components were
also positioned taking into account the size of the air vents and the exhaust pipes. Finally,
although safety was not an issue considered at this stage, the battery pack was placed on the
main frame, under the rear seats, in order to abide by the “crash protection” requirements and
to be easily accessed for inspection, maintenance and replacement. The hybridization
procedure of an existing vehicle is, in practical engineering terms, relatively simple, and,
especially in the case of GT-hybrid, does not substantially modify the conventional vehicle
chassis. The components dimensions and weight are reported in the table.
Table 3. a) Sedan or Sports Car; b) City Car Configuration
W[N]aDimensions [mm]aW[N]bDimensions [mm]b
Battery package 1274 850x400x185 784 510x400x185
Electric Motor/Generator 392 Ø264x315 392 Ø264x315
GT + regenerator 490 850x500x300 294 700x500x300
GT fuel tank 343 Ø270x800 343 Ø270x800
Inverter 147 410x340x130 147 410x340x130
Total power train weight 2646 1960
Passenger Sedan & Sports Car
The battery weighs 130 kg and is located underneath the rear seats. The gas tank is in the aft
section while all remaining components are housed in the front section. The weight
distribution is 1775 N (181 kg) on the fore-axle and 1832 N (187 kg) on the rear axle, for a
49/51 ratio (Figure 8).
City Car
The battery weighs 80 kg and is underneath the rear seats. The gas tank is in the aft section
while all remaining components are housed in the front section. The weight distribution is the
following one. 1432 N (146 kg) on the fore-axle and 912 N (93 kg) on the rear axle, for a 61/
39 ratio (Figure 10). The vehicle frame from is an Audi A2 one.
Figure 8. Components packaging and weights distribution for the sedan/sports and city car
6. Feasibility Analysis
The results obtained from the preliminary feasibility analysis, reflects the desired savings,
reducing consumption of all proposed configurations. A summary of the data is presented
below.
Table 4. Savings evaluation between the commercial (diesel) and hybrid configuration
Vehicle Emissions Fuel Consumption [l / 100 km]
Before After % gain Before After % gain
City car
Sedan
EURO 5
EURO 5
EURO 6
EURO 6
Yes
yes
5.2
16.4
2.9
9.7
45
40
Despite a considerable fuel consumptions savings can be notice, this gain would not be
immediate, and then it was necessary to proceed with an investment analysis to assess a
reasonable payback time (PB). The calculation of the PB was calculated using the following
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formula indicating the relationship between the initial cost of investment divided by the
difference between the daily costs before and after the conversion.
PB = Initial investment / [(Annual vehicle cost) – (Annual hybrid vehicle cost)] (17)
The annual expenditure can be calculated as:
reference vehicle=
[
A ∙ E ∙ F
100
]
∙ B
(18)
hybrd diesel vehicle=
[
A ∙ E ∙ G
100
]
∙ B
(19)
hyrid methane vehicle=
[
A ∙ E ∙ H
100
]
∙ C
(20)
hybrid CNG vehicle =
[
A ∙ E ∙ I
100
]
∙ D
(21)
In Table 5 the summary data calculations for city cars and sedan are listed. Following the
same procedure see above, it has been chosen to estimate a 100 city cars replacement and 800
passenger sedan.
Table 5. Income statement in the implementation of city car and sedan, respectively
A To Replace [unit] 100 A To Replace [unit] 800
B Diesel price [$/l]1.35 B Diesel price [$/l]1.35
C Methane [$/kg] 0.5 C Methane [$/kg] 0.5
D CNG [$/l]0.7 D CNG [$/l]0.7
E Car annual range [km] 10000 E Car annual range [km] 15000
F Reference fuel consumption 5.2 l/ 100 km F Reference fuel consumption 17.5 l/ 100 km
G Diesel fuel consumption 3.5 l/ 100 km G Diesel fuel consumption 16.4 l/ 100 km
H Methane fuel consumption 4.4 kg/ 100 km H Methane fuel consumption 7.3 kg/ 100 km
I CNG fuel consumption 5.8 l/ 100 km I CNG fuel consumption 9.7 l/ 100 km
PBdiesel 6018 days PBdiesel 223.4 days
PBmethane 3853 days PBmethane 132 days
PBCNG 7066 days PBCNG 180 days
For city cars, the return on investment are much higher than the previous case. At least 10
years would be needed to achieve a gain, in the best configuration, once definitely not
possible. The proposal in this case would be to proceed with smaller groups of cars on which
evaluate the investment or to change the choice of battery with a cheaper solution, to gain
more reasonable PB period. Finally, in the same way, the PB of a passenger sedan has been
calculated. It can be notice that, the solution hybrid-diesel is to be discarded, given the
excessive PB. The other two solutions, Methane Hybrid and CNG Hybrid, are very
interesting, with a lower PB. All depends on the increased number of substituted vehicles and
annual range (see table 7 for reference)
7. Final remarks
Summarizing and interpreting the results it can be stated as follows. The feasibility of the
project has been amply demonstrated. The most important aspect reached is the reduction of
the fuel consumption. Therefore, also decrease polluting emissions. Thanks to this, all
vehicles are widely on the EURO VI class. The reduction in consumption leads to a capital
gain that can invest in vehicles maintenance and development. The most suitable fuel is the
CNG, but is affected by the scarcity of gas stations. This inconvenience is negligible in the
case that a planned supply plan is organized. The study of possible real-world implementation
involves an initial configuration, which may be the subject of possible future studies related
to its optimization. The choice of commercial components is also a pre-proposal and
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therefore susceptible of improvement. Currently, it is known, that the proposed study is a
research level, but it is the last step before prototyping phase. But it is the last step before
prototyping phase, that is linked, inevitably, to the research of investment funds. The
hybridization of the current fleet of vehicles could be seen as a first step toward a revolution
in the transport sector, which necessarily must aim for a total reduction of fuel consumption
and emissions in the short term.
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Kliton Bylykbashi
Eng. Kliton Bylykbashi (born Tirana 28/05/1984, M. Eng. 2010, First Level Master Degree
2012: Industrial Production Engineering; Second Level Master Degree 2014: Energy
Efficiency and Renewvable Energy ), is Ph.D. Student a Sapienza University of Rome, at
Astronautics, Electrical and Energy^Engineering Department (DIAEE), where is a lecture of
Energy System 1 and 2. He is a scientific collaborator at CREA Ing..
His currently active research topics are modeling of low environmental impact systems for
farming industry and exergy valutation of complex system. From 2012 he carries out a
technical consultant in Mechanics and Enegrgetic engineering, developing PV, Wind, Bigas
and CHP system and design diagnostic and energy saving of the energy systems.
^
Roberto Capata
Born in Rome, November 1968. M. Eng. In Mechanical Engineering, 1994, University of
Roma^ “Sapienza.” Ph.D. in Energy Engineering, University of Rome 1, May 2000. Presently
Assistant Adjoint Professor of Turbo machinery at University of Rome, Professor of^
Machine diagnosis at Department of Electric and Energetic Engineering,^ Professor of
Machine design^ at Department of Chemical Engineering and Biomedical Engineering.
Editorial Member of Thermal Energy and Power Engineering Journal, reviewer for several
ASME transactions (JERT, EGY), for Energies. Guest editor for Energies journal. Owner of
two patent on innovative micro chamber for gas turbine, and for on board ORC (Organic
Rankine cycle) systems. Author of several paper on international journal on turbomachinary,
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components design and realization, experimental tests on ORC systems, Advanced energy
systems.
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