Article citation information:
Garbala, K., Piekarski, W., Andrzejewska, S., Witaszek, K. Analysis of
operating parameters and indicators of a compression ignition engine fuelled
with LPG. Scientific Journal of
Krzysztof
GARBALA[1], Wojciech PIEKARSKI[2], Sylwia ANDRZEJEWSKA[3], Kazimierz WITASZEK[4]
ANALYSIS
OF OPERATING PARAMETERS AND INDICATORS OF A COMPRESSION IGNITION ENGINE
FUELLED WITH LPG
Summary. This article presents the possibilities for using alternative fuels to
power vehicles equipped with compression ignition (CI) engines (diesel).
Systems for using such fuels have been discussed. Detailed analysis and
research covered the LPG STAG autogas system, which is used to power dual-fuel
engine units (LPG+diesel). A description of the operation of the autogas
system and installation in a vehicle has been presented. The basic algorithms
of the controller, which is an actuating element of the whole system, have been
discussed. Protection systems of a serial production engine unit to guarantee
its factory-controlled durability standards have been presented. A
long-distance test drive and examinations of the engine over 150,000 km in a
Toyota Hilux have been performed.
Operating parameters and performance indicators of the engine with STAG
LPG+diesel fuelling have been verified. Directions and perspectives for the
further development of such a system in diesel-powered cars have been also
indicated.
Keywords: Diesel
engines; dual-fuel (LPG+diesel); STAG LPG+diesel
1. INTRODUCTION
In the last decade, a growing
interest among the authors of research papers published in industry magazines
on the issue of supplying CI engines (diesel) with gas fuels has been observed.
This is partly caused by the economic reasons, which directly influence a
reduction in the costs of the operation of the vehicle. In the case of high
mileage, the operation of such a car is clearly less expensive. Savings
can be up to around 35%, which means that the ROI time for the autogas system
installation is short. The use of alternative fuels to power diesel engines in
cars allows strict exhaust emission standards to be met without the necessity
of using complex systems for the neutralization of toxic components in fumes.
In the process of diesel combustion combined with LPG combustion, the vehicle
generates a reduced amount of the harmful components found in fumes (carbon
monoxide, carbon dioxide, nitrogen oxides and PM particles), thus, it is more
environmentally friendly. Such a supply can be an alternative to electrical
motors, particularly in trucks, where the installation of electrical drives is
limited by the drive distances and total weight [1-4].
2. CHARACTERISTICS OF FUELS USED TO SUPPLY
DIESEL ENGINES
The
conventional fuel used to power CI engines is diesel. This is a mixture of
hydrocarbons containing 14÷20 atoms of carbon per molecule, which has
a boiling temperature within the range of 150°C÷380°C. Diesel is
manufactured from petroleum with a secondary processing of the heavy
fractions left from petroleum distillation. Its properties must be modified
through special additives, which improve fuel performance, even when small
amounts are added. Fuel obtained in this way does not meet all the requirements
as diesel includes paraffinic and naphthenic hydrocarbons, as well as aromatic
hydrocarbons [5].
The amount
of individual hydrocarbon fractions in diesel has an impact on its physical and
chemical properties. This influences the parameters and performance indicators
of operating engines, particularly on the toxicity of fumes and the engine’s
operating efficiency. The high content of aromatic hydrocarbons makes the fuel
self-ignition delay longer, which causes a generation of build-ups in the
combustion chamber and increases emission of solid particles. This, in turn,
leads to a reduction of the content of heavy hydrocarbons and sulphur in
diesel, which influences the lubricity and density. Additionally, fuels for
diesel engines should have the following properties: high capabilities of
spraying, mixing with air and evaporating, which influences cold engine starts.
The important properties of diesel include the ability to generate
self-ignition after the injection of a measured dose of fuel to the cylinder
and to achieve full and complete combustion. This is influenced by many
factors, such as fractional composition, viscosity, volatility, surface
tension, density, solidification and cloud point. Paraffinic hydrocarbons show
the best ability to self-ignite. Their disadvantage is the high solidification
temperature, which causes the blocking of the engine fuelling system in low
ambient temperatures [6, 7].
The leading trend in the development of modern CI engines (diesel) is the
search for and application of various alternative fuels. Such fuels may include
vegetable oils or their esters, ethers, alcohols, LPG, CNG or LNG, biogas,
hydrogen or synthetic fuels [8, 9].
3. POSSIBILITIES OF SUPPLYING DIESEL ENGINES
WITH LPG
CI engines have been fuelled only
with diesel oil for years. This fuel shows good self-ignition properties (high
cetane number). While LPG-type fuels show a high octane number and a high
resistance to spontaneous ignition as a consequence. This causes problems with
using this fuel to power diesel engines. This is why a combination of both
diesel and LPG is needed. Supplying LPG to a diesel engine can be carried out
by using various methods [10, 11]:
- mixer,
- injector
assembly in the intake manifold,
- injector
delivering fuel via the suction valve,
- injector
in the combustion chamber.
4. LPG
STAG AUTOGAS SYSTEM FOR POWERING DUAL-FUEL ENGINE UNITS (LPG+DIESEL)
With the
development of the automotive industry and market demand for gas systems for vehicles
equipped with CI engines (diesel), the Centre for Research and Development of
AC S.A. started research work into commercial LPG systems dedicated for such
systems. The work made use of the extensive experience with LPG systems
for spark-ignited engines. High requirements were set for future LPG systems
supporting diesel engines. The focus was put on operational properties,
such as the life and durability of the engine unit. From a commercial
point of view, it is the first and most important criterion specified for such
systems. Economic and performance factors were also taken into consideration,
as they are equally important.
The
dual-fuel system allows us to extract energy from new diesel resources (e.g.,
burning solid particles in the cylinder). If the autogas installation is
properly installed and tuned, it is possible to gain a significant increase in
power and torque by 10%÷30%, while reducing the operating costs and
improving engine parameters and performance indicators. In diesel engines with
a mechanical injection, the gas is injected into the intake manifold, which
results in a more efficient burning of diesel, the additional combustion of gas
increases the power of the engine and the combustion thermodynamic efficiency
is improved. The vehicle shows better dynamic qualities thanks to the power and
torque increase. Financial benefits (savings) are present in both dynamic
driving and eco-driving [12].
The
controller is an important element of such an autogas system. For the needs of
CI engines, a new design of a controller specifically dedicated to such engines
(STAG diesel controller) has been introduced. It can be used for fuelling 2÷16
cylinder engine units. The whole system has been based on the latest
technical and technological solutions, enabling the dosing of the gas fuel with
air, which are then mixed with diesel in the cylinder. The controller does
not exclude driving on diesel oil alone, as the autogas system does not
interfere with the internal parts of the engine. The controller is capable of
the intelligent controlling of the fuel dosing process during engine operation.
This is possible when the following sensor measurements are read: exhaust
temperature or oxygen sensor (lambda probe). An advanced algorithm for
sequential gas injection is based on the current demand for fuel. Measurements
cover the amount of injected oil as well. The engine protection system has been
extended with a temperature control system for the safety of the unit. The
system is also able to read the ATF ratio and control it with an independent
wideband lambda probe dedicated for CI engines (diesel). Figure 1 presents
the STAG diesel controller, while Table 1 describes its functions and its
technical and operating capabilities.
Fig. 1. STAG diesel controller and LPG STAG R02 reducer
Table 1.
Key technical
parameters of the STAG diesel controller
|
Supported engines |
Diesel with mechanical injection |
|
Diesel with common rail electronic injection |
|
|
Diesel with unit injectors |
|
|
Fumigation options |
LPG or CNG |
|
Control systems and
algorithms |
Advanced algorithm of sequential gas injection |
|
Precise gas dosing based on current engine demand |
|
|
Measurements and
control of injected diesel in common rail engines |
|
|
Advanced
algorithm for engine protection |
|
|
Controlled
exhaust gas temperature for improved safety of the drive unit |
|
|
Reading a
wideband oxygen sensor, control of air-to-fuel rate with an independent
wideband oxygen sensor designed for diesel engines (optional installation |
|
|
Support for cars
provided with cruise control |
|
|
Modification of
gas injection sequence |
For the
purpose of gas pressure reduction, the STAG R02 reducer (Fig. 1) was used.
The basic features distinguishing the STAG R02 are the compact size and
unique design, including two aluminium castings and Actherm-rated cover, which
prevents gas cooling, thus, providing excellent thermal insulation. Due to its
unique design, the AC R02 heats up very quickly, such that switching to gas is
also performed quickly. Therefore, no additional work, such as temperature
correction, is required of the controller. Its high thermal efficiency and
resistance to LPG contamination make the reducer the best option when selecting
autogas system components. Table 2 presents the technical specification of the
applied reducer.
Table 2.
Technical
specifications of the LPG STAG R02 reducer
|
Material |
Two aluminium castings and a cover made of
hard, resistant plastic |
|
Weight |
1.56 kg |
|
Dimensions |
125x122x89 |
|
Maximum
inlet pressure |
30 bar |
|
Outlet
pressure |
0.9-1.5 bar |
|
Gas
inlet diameter |
M10x1 |
|
Gas
outlet diameter |
Hose Ø12 |
|
Water
outlet diameter |
Ø16 |
|
Maximum
engine power |
100 kW (136 hps) |
|
Approval |
67 R - 01 6865 |
The LPG
supply system was equipped with the ACW01 injection rail (Fig. 2). This type of
injector is designed for sequential gas injection in compression injection and
spark injection engines. It ensures the precise dosing of vaporized gas to the
intake duct separately for each engine cylinder. As with all other AC injection
rails, this rail exhibits high durability, which has been confirmed in
long-distance road tests for various makes of car and various road and weather
conditions. Additionally, the AC rail is provided with 2Ω coils, which
eliminate the risk of overloading the control systems. The coils have been
equipped with IP67-rated connections. The main component is the body, which is
made of anodized aluminium. The connections are made of brass, while the
sealing is based on rubber compounds compatible with other elements. The
technical specification of this injection rail is presented in Table 3.
Fig. 2. ACW01 injector
rail
Table 3.
Technical
specifications for the ACW01 injection rail
|
Rated operating pressure |
0.95÷1.2 bar |
|
Maximum operating pressure |
4.5 bar |
|
Injector opening time |
~2.1 ms |
|
Injector closing time |
~1.5 ms |
|
Performance range |
11÷29 kW/cylinder |
|
Maximum flow |
90 l/min for p=1 bar |
5. TESTING THE OPERATING PARAMETERS OF A
COMPRESSION IGNITION ENGINE FUELED WITH LPG
The STAG
diesel system was installed in a new Toyota Hilux with a CI engine. Figure 3
presents the vehicle (test unit) with the locations of the LPG system
components. Table 4 specifies the technical parameters of the Toyota Hilux.
Measurements and test drives of the LPG+diesel system were performed over
a distance of 150,000 kilometres.
Test-driving was performed in the
city, on express roads, on country drives and under extreme conditions
(off-road). This mode of testing offered an exact representation of the operating
conditions for this type of vehicle. Figure 4 presents a diagram of the STAG
diesel in the LPG+diesel system.
Table
4.
Technical (factory) specifications
of the test vehicle, Toyota Hilux
|
Type |
Pickup |
|
Year of
manufacture |
2012 |
|
Emission
standard compliance |
EURO 5 |
|
Engine type |
Turbocharged
with an intercooler |
|
Capacity |
2,494 cm2 |
|
Number of
cylinders |
4 |
|
Fuel supply |
Common rail
with electronic injection control |
|
Maximum power |
106 kW at
engine rpm of 3,400 |
|
Maximum torque |
343 Nm at engine rpm of 2,000 |
|
Maximum speed |
|
|
Transmission |
Five-gear,
manual |
Fig. 3. View of the test unit (vehicle) with the locations of the LPG
system components
Technical inspections of the engine
were performed every 10,000 km. These checks involved measurements of the
compression ratio and valve clearance. Inspections of the cylinder working
faces, valve guides and valves (valve face) were also carried out. Visual
inspections of these elements were performed with the use of an endoscope. The
results of engine unit tests were compared with the manufacturer’s
requirements.
It was observed that the wear of
individual components did not exceed the factory limits. Therefore, it can be
concluded that the installation of an LPG+diesel fuelling system does not
significantly affect the durability of the engine unit.
Figure 5 presents the speed
characteristics of the tested vehicle. The measurements of the torque and
power trends vs. rpm were performed for the three fuelling systems:
- only diesel,
- only LPG+diesel.
Analysis of the curves shows an increase in torque and power, respectively. The engine power increase in the LPG+diesel mode was 20 hp and the torque increase was 42 Nm. Analysis of torque curves indicates a shift in the maximum torque towards higher engine speeds. This results in a lower ratio of engine flexibility to its power. As a consequence, the engine is more dynamic, which directly influences acceleration in different gears.
Long-term tests covering
150,000 km in urban, country and off-road conditions allowed us to estimate the
economy of the dual-fuel system: the average reduction of the operating costs
related to the engine demand for diesel in mixed cycles was 31%.
Fig. 4.
Diagram of the STAG diesel-based LPG+diesel system
Fig. 5. Power and torque
characteristics of the tested vehicle
6. CONCLUSION
Summing up the results of the tests
presented in the research paper leads to the conclusion that there are
extensive possibilities for the application and development of CI engines with
dual-fuel (LPG+diesel) systems. This is supported by the excellent distribution
of LPG fuelling stations in Poland. It is a very important element for vehicle
operation, as the number of CNG stations in still limited in Poland.
Using the fuelling system presented
in the tested vehicle ensures a reduction in the operating costs related
to fuel by 31% when compared to diesel. Additionally, the power and torque
levels were observed to be 20% higher, which makes the car much more dynamic to
drive. A further benefit of the dual-fuel system is the reduction of
harmful exhaust gases, resulting from the limited emissions of nitrogen oxides,
solid particles and carbon dioxide, which are released into the natural
environment. Long-term operating tests over a distance of 150,000 km were
performed under urban, country and off-road conditions, confirming the reliability
of dual-fuel (LPG+diesel) systems. The results of the inspections of the
technical condition of the engine did not show any increased wear on the
engine components, which means that the engine parameters remain within
the standards and technical specifications of the manufacturer.
References
1.
Tiraa H.S., J.M. Herrerosb, A. Tsolakisa, M.L.
Wyszynski. 2012. “Characteristics of LPG-diesel dual fuelled engine operated
with rapeseed methyl ester and gas-to-liquid diesel fuels”. Energy 47(1): 620-629.
2.
Poonia M.P., A. Ramesh, R.R. Gaur, A. Joshi.
2012. “Effect of pilot fuel quantity, injector needle lift pressure and load on
combustion characteristics of a LPG diesel dual fuel engine”. International Journal of Engineering and
Innovative Technology 2(1):
26-31.
3.
Deo Raj Tiwari, Sinha P. Gopal. 2014. “Performance
and emission study of LPG diesel dual fuel engine”. International Journal of Engineering and Advanced Technology 3(3):
198-203.
4.
Ashok B. Ashok S. Denis, Kumar C. Ramesh.
2015. “LPG diesel dual fuel engine: a critical review”. Alexandria Engineering Journal 54(2):
105-126.
5.
Baczewski K., T. Kałdoński. 2004. Fuels
for Diesel engines. Warsaw: Transport and Communication Publishers.
6.
Lotko W., R. Longwic, K. Górski. 2000. “Study of chosen parameters of the combustion
process of diesel fuel in transient conditions”. Journal of KONES Internal Combustion Engines 7(1-2): 330-341.
7.
Samaras Z. 1999. “Emissions reduction via improvements in engines and
fuels: the Tehran case”. Journal of
Urban Technology 6(1): 63-87.
8.
Subbaiah1 G.V., K.R. Gopal. 2011. “An experimental investigation on the
performance and emission characteristics of a diesel engine fuelled with rice
bran biodiesel and ethanol blends”. International
Journal of Green Energy 8: 197-208.
9.
McTaggart-Cowan G.P., C.C.O. Reynolds, W.K. Bushe. 2006. “Natural gas
fueling for heavy-duty on-road use: current trends and future direction”. International Journal of Environmental
Studies 63(4): 421-440.
10.
Ambrozik,
A., P. Kruczyński, P. Orliński. 2003. “Influence of diesel engine fueling with
different fuels on self-ignition delay in aspect of ecology”. Eksploatacja I Niezawodnosc –
Maintenance and Reliability 3: 50-55.
11.
Luft S. 2003. “Dual-fuel compression ignition
engine: selected problems of combustion process”. Journal of KONES Internal Combustion Engines 11(3-4): 31-38.
12.
Unpublished research data of
the Centre for Research and Development of AC S.A.
Received 12.05.2016;
accepted in revised form 25.08.2016
Scientific Journal of