Direct injection of hydrogen main fuel and diesel pilot fuel in a retrofitted single-cylinder compression ignition engine

Up to 90% hydrogen energy fraction was achieved in a hydrogen diesel dual-fuel direct injection (H2DDI) light-duty single-cylinder compression ignition engine. An automotive-size inline single-cylinder diesel engine was modified to install an additional hydrogen direct injector. The engine was operated at a constant speed of 2000 revolutions per minute and fixed combustion phasing of ?10 crank angle degrees before top dead centre (°CA bTDC) while evaluating the power output, efficiency, combustion and engine-out emissions. A parametric study was conducted at an intermediate load with 20–90% hydrogen energy fraction and 180-0 °CA bTDC injection timing. High indicated mean effective pressure (IMEP) of up to 943 kPa and 57.2% indicated efficiency was achieved at 90% hydrogen energy fraction, at the expense of NO_x emissions. The hydrogen injection timing directly controls the mixture condition and combustion mode. Early hydrogen injection timings exhibited premixed combustion behaviour while late injection timings produced mixing-controlled combustion, with an intermediate point reached at 40 °CA bTDC hydrogen injection timing. At 90% hydrogen energy fraction, the earlier injection timing leads to higher IMEP/efficiency but the NO_x increase is inevitable due to enhanced premixed combustion. To keep the NO_x increase minimal and achieve the same combustion phasing of a diesel baseline, the 40 °CA bTDC hydrogen injection timing shows the best performance at which 85.9% CO₂ reduction and 13.3% IMEP/efficiency increase are achieved.     

Effect of hydroxy (HHO) gas addition on performance and exhaust emissions in compression ignition engines

In this study, hydroxy gas (HHO) was produced by the electrolysis process of different electrolytes (KOH_(aq), NaOH_(aq), NaCl_(aq)) with various electrode designs in a leak proof plexiglass reactor (hydrogen generator). Hydroxy gas was used as a supplementary fuel in a four cylinder, four stroke, compression ignition (CI) engine without any modification and without need for storage tanks. Its effects on exhaust emissions and engine performance characteristics were investigated. Experiments showed that constant HHO flow rate at low engine speeds (under the critical speed of 1750 rpm for this experimental study), turned advantages of HHO system into disadvantages for engine torque, carbon monoxide (CO), hydrocarbon (HC) emissions and specific fuel consumption (SFC). Investigations demonstrated that HHO flow rate had to be diminished in relation to engine speed below 1750 rpm due to the long opening time of intake manifolds at low speeds. This caused excessive volume occupation of hydroxy in cylinders which prevented correct air to be taken into the combustion chambers and consequently, decreased volumetric efficiency was inevitable. Decreased volumetric efficiency influenced combustion efficiency which had negative effects on engine torque and exhaust emissions. Therefore, a hydroxy electronic control unit (HECU) was designed and manufactured to decrease HHO flow rate by decreasing voltage and current automatically by programming the data logger to compensate disadvantages of HHO gas on SFC, engine torque and exhaust emissions under engine speed of 1750 rpm. The flow rate of HHO gas was measured by using various amounts of KOH, NaOH, NaCl (catalysts). These catalysts were added into the water to diminish hydrogen and oxygen bonds and NaOH was specified as the most appropriate catalyst. It was observed that if the molality of NaOH in solution exceeded 1% by mass, electrical current supplied from the battery increased dramatically due to the too much reduction of electrical resistance. HHO system addition to the engine without any modification resulted in increasing engine torque output by an average of 19.1%, reducing CO emissions by an average of 13.5%, HC emissions by an average of 5% and SFC by an average of 14%.     

Effect of induction on exhaust gas recirculation and hydrogen gas in compression ignition engine with simarouba oil in dual fuel mode

Biofuels extracted from non-edible oil is sustainable and can be used as an alternative fuel for internal combustion engines. This study presents the performance, emission and combustion characteristic analysis by using simarouba oil (obtained from Simarouba seed) as an alternative fuel along with hydrogen and exhaust gas recirculation (EGR) in a compression ignition (CI) engine operating on dual fuel mode. Simarouba biofuel blend (B20) was prepared on volumetric basis by mixing simarouba oil and diesel in the proportion of 20% and 80% (v/v), respectively. Hydrogen gas was introduced at the flow rate of 2.67 kg/min, and EGR concentration was maintained at 30% of total air introduction. Performance, combustion and emission characteristics analysis were examined with biodiesel (B20), biodiesel with hydrogen substitution and biodiesel, hydrogen with EGR and were compared with neat diesel operation. Results indicate that BTE of the engine operating with biodiesel B20 was decreased when compared to neat diesel operation. However, introducing hydrogen along with B20 blend into the combustion chamber shows a slight increase in the BTE by 1%. NO_x emission was increased to 18.13% with the introduction of hydrogen than that of base fuel (diesel) operation. With the introduction of EGR, there is a significant reduction in NO_x emission due to decrease in in-cylinder temperature by 19.07%. A significant reduction in CO, CO_2, and smoke emissions were also noted with the introduction of both hydrogen and EGR. The ignition delay and combustion duration were increased with the introduction of hydrogen, EGR with biodiesel than neat diesel operation. Hence, the proposed biodiesel B20 with H₂ and EGR combination can be applied as an alternative fuel in CI engines.     

A review of ammonia as a compression ignition engine fuel

During the past decades, the diesel engine has been through times of upheaval, boom and bust. At the beginning of the century, almost 50% of the new vehicle registrations in the European market were diesel-powered. However, the news of deadly diesel NO_x emissions supported by the diesel emission scandals caused a shock to the diesel engine market, and the sustainability of the diesel engine is currently in dispute.Recently major automotive manufacturers announced the development of diesel-powered vehicles with negligible NO_x emissions. Moreover, the NO_x emissions production is of lower concern for heavy-duty, marine or power generations applications where the implementation of advanced aftertreatment systems is feasible. However, despite the tackle of NO_x emissions, the decarbonisation of the automotive, marine and power generation markets is mandatory for meeting greenhouse gas emissions targets and limiting global warming.The decarbonisation of the diesel engine can be achieved by the implementation of a carbon-free fuel such as ammonia. This paper provides a detailed overview of ammonia as a fuel for compression ignition engines. Ammonia can be combusted with diesel or any other lower autoignition temperature fuel in dual-fuel mode and lead to a significant reduction of carbon-based emissions. The development of advanced injection strategies can contribute to enhanced performance and overall emissions improvement. However, ammonia dual-fuel combustion currently suffers from relatively high unburned ammonia and NO_x emissions because of the fuel-bound nitrogen. Therefore, the implementation of aftertreatment systems is required. Hence, ammonia as a compression ignition fuel can be currently seen as a feasible solution only for marine, power generation and possibly heavy-duty applications where no significant space constraints exist.     

A review of hydrogen as a compression ignition engine fuel

Diesel fuelled engines emit higher levels of carbon dioxide and other harmful air pollutants (such as noxious gases and particulates) per litre of fuel than gasoline engines. This fact, combined with the recent diesel emission scandal and the rumours of more widespread cheating by automotive manufacturers have initiated a long discussion about the future and sustainability of diesel engines.Improving the compression ignition engine is a direct way of going green. Reducing the harmful emissions can be achieved by future developments in the engine technology but also the implementation of alternative fuels. Hydrogen is a renewable, high-efficient and clean fuel that can potentially save the future of diesel-type engines. The evolution of high-efficiency renewable hydrogen production methods is the most important path for the start of a new hydrogen era for the compression ignition engine that can improve its sustainability and maximum efficiency.This paper provides a detailed overview of hydrogen as a fuel for compression ignition engines. A comprehensive review of the past and recent research activities on the topic is documented. The review focuses on the in-cylinder combustion of hydrogen either as a primary fuel or in dual fuel operation. The effects of injection strategies, compression ratio and exhaust gas recirculation on the combustion and emission characteristics of the hydrogen fuelled engine are fully analysed. The main limitations, challenges and perspectives are presented.     

Experimental investigation of the effect of hydrogen ratio on engine performance and emissions in a compression ignition single cylinder engine with electronically controlled hydrogen-diesel dual fuel system

In recent years, there has been a rapid transition from internal combustion engines to hybrid and electric vehicles. It is an inevitable fact that the dominance of internal combustion engines in the market will continue for many years due to the charging and battery problems in these vehicles. Therefore, it is an important issue to improve the performance and emissions of internal combustion engines by making them work with alternative energy sources. In this study, hydrogen-diesel dual fuel mode was used in a dual-fuel compression ignition single cylinder engine with common rail fuel injection system and electronically controlled gas fuel system. The study was carried out at constant speed (1850 rpm), different load (3-4.5-6-7.5-9 Nm) and different hydrogen injector opening amounts (1.6-1.8-2.0 ms). The effects of hydrogen energy ratios obtained with different hydrogen injector opening amount on engine performance and emissions were examined. According to the results, it was determined that the in-cylinder pressure values increased at medium and high loads, and the specific energy consumption decreased. When the emission values were examined, it was determined that there was an increase in NO emissions and a significant decrease in other emissions. However, increasing the hydrogen energy ratio above 14% adversely affected engine performance and emissions.     

Experimental investigation on biogas enrichment with hydrogen for improving the combustion in diesel engine operating under dual fuel mode

Biogas valorization as fuel for internal combustion engines is one of the alternative fuels, which could be an interesting way to cope the fossil fuel depletion and the current environmental degradation. In this circumstance, an experimental investigation is achieved on a single cylinder DI diesel engine running under dual fuel mode with a focus on the improvement of biogas/diesel fuel combustion by hydrogen enrichment. In the present investigation, the mixture of biogas, containing 70% CH₄ and 30% CO₂, is blended with the desired amount of H₂ (up to 10, 15 and 20% by volume) by using MTI 200 analytical instrument gas chromatograph, which flow thereafter towards the engine intake manifold and mix with the intake air. Depending on engine load conditions, the volumetric composition of the inducted gaseous fraction is 20–50% biogas, 2–10% H₂ and 45–78% air. Near the end of the compression stroke, a small amount of diesel pilot fuel is injected to initiate the combustion of the gas–air mixture. Firstly, the engine was tested on conventional diesel mode (baseline case) and then under dual fuel mode using the biogas. Consequently, hydrogen has partially enriched the biogas. Combustion characteristics, performance parameters and pollutant emissions were investigated in-depth and compared. The results have shown that biogas enriched with 20% H₂ leads to 20% decrease of methane content in the overall exhaust emissions, associated with an improvement in engine performance. The emission levels of unburned hydrocarbon (UHC) and carbon monoxide (CO) are decreased up to 25% and 30% respectively. When the equivalence ratio is increased, a supplement decrease in UHC and CO emissions is achieved up to 28% and 30% respectively when loading the engine at 60%.     

Analysis of combustion mode and operating route for hydrogen fueled scramjet engine

Hydrogen fueled scramjet is a candidate for use as the engine of the aerospace plane for its high specific impulse. To further improve the specific impulse performance, analysis of combustion mode and operating route for a hydrogen fueled scramjet engine was investigated in this study. A scramjet engine with two-staged hydrogen injection was simulated by one-dimension numeric method within the acceleration from Mach 4 to 7. Three typical combustion modes (scramjet-mode, transitional mode and ramjet-mode) could be attained by changing the total amount of fuel added or adjusting the fuel distribution between two injectors. Simulation results show that better thrust performance can be achieved as more fuel injected at the upstream fuel injector as possible, while ensuring the engine safety. From a standpoint of specific impulse maximization, an optimal scramjet combustion mode database was presented and the boundary of the combustion mode transition was determined. Meanwhile, optimal operating route was also suggested for scramjet operation in this study.     

Analysis of CRDI diesel engine characteristics operated on dual fuel mode fueled with biodiesel-hydrogen enriched producer gas under the single and multi-injection scheme

The present work aims to investigate the consequences of pilot fuel (PF) multiple injections and hydrogen manifold injection (HMI) on the combustion and tailpipe gas characteristics of a common rail direct injection (CRDI) compression ignition (CI) engine operated on dual fuel (DF) mode. The CI engine can perform on a wide variety of fuels and under high pilot fuel (PF) pressure. Pilot fuel injection (PFI) is achieved at TDC, 5, 10, and 15ºCA before the top dead center (bTDC), and divided injection consists of injecting fuel in three different magnitudes on a time basis and PF is injected into the engine cylinder at a pressure of 600 bar. In this work, the hydrogen flow rate (HFR) was fixed at 8 lpm constant and producer gas was inducted without any restriction. The investigational engine setup has the ability to deliver a PF and hydrogen (H₂) precisely in all operating circumstances using a separate electronic control unit (ECU). Results showed that diesel-hydrogen enriched producer gas (HPG) operation at maximum operating conditions provided amplified thermal efficiency by 4.01% with reduced emissions, except NOx levels, compared to biodiesel-HPG operation. Further, DiSOME with the multi-injection strategy of 60 + 20+20 and 50 + 25+25, lowered thermal efficiency by 4.8% and 9.12%, respectively compared to identical fuel combinations under a single injection scheme. However, reductions in NOx levels, cylinder pressure, and HRR were observed with a multi-injection scheme. It is concluded that multi-injection results in lower BTE, changes carbon-based emissions marginally, and decreases cylinder pressure and heat release rate than the traditional fuel injection method.     

Effects of split injection proportion and the second injection timings on the combustion and emissions of a dual fuel SI engine with split hydrogen direct injection

In this paper, a new kind of injection mode, split hydrogen direct injection, was presented for a dual fuel SI engine. Six different first injection proportions (IP1) and five different second injection timings were applied at the condition of excess air ratio of 1, first injection timing of 300°CA BTDC, low speed, low load conditions and the Minimum spark advance for Best Torque (MBT) on a dual fuel SI engine with hydrogen direct injection (HDI) plus port fuel injection (PFI). The result showed that, split hydrogen direct injection can achieve a higher brake thermal efficiency and lower emissions compared with single HDI. In comparison with single HDI, the split hydrogen direct injection can form a controlled stratified condition of hydrogen which could make the combustion more complete and faster. By adding an early spray to form a more homogeneous mixture, the split hydrogen direct injection not only can help to form a flame kernel to make the combustion stable, but also can speed up the combustion rate through the whole combustion process, which can improve the brake thermal efficiency. By split hydrogen direct injection, the torque reaches the highest when the first injection proportion is 33%, which improves by 1.13% on average than that of single HDI. With the delay of second injection timing, the torque increases first and then decreases. With the increase of first injection proportion, the best second injection timing is advanced. Furthermore, by forming a more homogeneous mixture, the split hydrogen direct injection can reduce the quenching distance to reduce the HC emission and reduce the maximum temperature to reduce the NO_X. The split hydrogen direct injection can reduce the HC emission by 35.8%, the NO_X emissions by 7.3% than that of single HDI.     

Optimisation of dry cell electrolyser and hydroxy gas production to utilise in a diesel engine operated with blends of orange peel oil in dual-fuel mode

This study aims at producing hydroxy (HHO) gas using a dry cell electrolysis setup and utilising it along with orange oil in a diesel engine. First an electrolyser was designed considering the optimised values of the material (SS316L), electrolyte (NaOH), and electrode gap (2 mm). Then the biodiesel obtained from the waste orange peels, after transesterification, were blended with diesel at 25 and 50% by vol. The HHO gas was produced by the water electrolysis method by a plate-type electrolyser having a maximum production rate of 2.5 LPM with NaOH as the electrolyte. HHO gas was inducted through the inlet manifold along with the fresh air at a constant rate of 2 LPM with both the biodiesel blends. The performance, emission, and combustion outcomes of the single cylinder diesel engine for different load conditions (0–100%) were tested for all the blends with and without HHO addition. The results showed a considerable increase in brake thermal efficiency of 1.54% at full load condition, with a noticeable decrease in fuel consumption by 11.1% compared to conventional diesel fuel, was achieved for the O25 blend with HHO induction. Moreover, emissions like hydrocarbon, carbon monoxide and smoke were reduced by 17.6, 29.5, and 12.1%, respectively. However, the improvement in combustion outcomes led to the increase in nitrogen oxides emission by 9.67%. This study helped to understand the production process of HHO gas by dry cell electrolyser and its effect on the blend of orange oil methyl ester and diesel in dual-fuel mode.     

Combustion,performance and emissions of ULSD,PME and B50 fueled multi-cylinder diesel engine with naturally aspirated hydrogen

An experimental study was conducted on a diesel engine fueled with ultra-low sulfur diesel (ULSD), palm methyl ester (PME), a blended fuel containing 50% by volume each of the ULSD and PME, and naturally aspirated hydrogen, at an engine speed of 1800 rev min⁻¹ under five loads. Hydrogen was added to provide 10% and 20% of the total fuel energy. The following results are obtained with hydrogen addition. There is little change in peak in-cylinder pressure and peak heat release rate. The influence on fuel consumption and brake thermal efficiency is engine load and fuel dependent; being negative for the three liquid fuels at low engine loads but positive for ULSD and B50 and negligible for PME at medium-to-high loads. CO and CO₂ emissions decrease. HC decreases at medium-to-high loads, but increases at low loads. NO_x emission increases for PME only but NO₂ increases for the three liquid fuels. Smoke opacity, particle mass and number concentrations are all reduced for the three liquid fuels.     

Combustion analysis of a spark ignition engine fueled with gaseous blends containing hydrogen

This paper presents the combustion characteristics of a naturally aspirated spark ignition engine, intended for installation in vehicles, fueled with different hydrogen and methane blends. The experimental tests were carried out in a wide range of speeds at equivalence ratios of 1, 0.8 and 0.7 and at full load. The ignition timing was maintained for each speed, independently of the equivalence ratio and blend used as fuel. Four methane-hydrogen blends were used. In-cylinder pressure, mass fraction burned, heat released and cycle-by-cycle variations were analyzed as representative indicators of the combustion quality. It was observed that hydrogen enrichment of the blend improve combustion for the ignition timing chosen. This improvement is more appreciable at low speeds, because at high speeds hydrogen effect is attenuated by the high turbulence. Also, hydrogen addition allowed the extension of the LOL, enabling the engine to run stable in points where methane could not be tested. The main inconvenience detected was the high NO_x emissions measured, especially at stoichiometric conditions, due mainly to the increment in the combustion temperature that hydrogen produces.     

Experimental investigations on the use of preheated animal fat as fuel in a compression ignition engine

The effect of fuel inlet temperature on performance, emission and combustion characteristics of a diesel engine is evaluated. A single cylinder direct injection diesel engine developing a power output of 2.8 kW at 1500 rev/min is tested using preheated animal fat as fuel. Experiments are conducted at the fuel inlet temperatures of 30, 40, 50, 60 and 70 °C. Animal fat at low temperature results in higher ignition delay and combustion duration than diesel. Preheated animal fat shows reduced ignition delay and combustion duration. Peak pressure and rate of pressure rise are found as high with animal fat at high fuel inlet temperatures. Heat release pattern shows reduced premixed combustion phase with animal fat as compared to neat diesel at normal temperature. Preheating improves the premixed combustion rate. At low temperature, animal fat results in lower smoke emissions than diesel. The maximum smoke density is K=6.5 m⁻¹ with diesel and K=3.6 m⁻¹ with animal fat at 30 °C. Preheated animal fat further reduces smoke levels at all temperatures. The smoke level is reduced up to K=1.7 m⁻¹ with preheated animal fat at the temperature of 70 °C. Hydrocarbon and carbon monoxide emissions are higher with animal fat at low temperature as compared to diesel. Fuel Preheating reduces these emissions. NO emission is found as low with animal fat at low temperature. Fuel preheating results in increased NO emission. However, the level is still lower than diesel even at high temperature (i.e. 70 °C). On the whole it is concluded that preheated animal fat can be used in diesel engines with reduced smoke, hydrocarbon and carbon monoxide emissions with no major detoriation in engine performance.     

Using HHO (Hydroxy) and hydrogen enriched castor oil biodiesel in compression ignition engine

Hydrogen and HHO enriched biodiesel fuels have not been investigated extensively for compression ignition engine. This study investigated the performance and emissions characteristics of a diesel engine fueled with hydrogen or HHO enriched Castor oil methyl ester (CME)-diesel blends. The production and blending of CME was carried out with a 20% volumetric ratio (CME20) using diesel fuel. In addition, the enrichment of intake air was carried out using pure HHO or hydrogen through the intake manifold with no structural changes – with the exception of the reduction of the amount of diesel fuel – for a naturally aspirated, four cylinder diesel engine with a volume of 3.6 L. Hydrogen amount was kept constant with a ratio of 10 L/min throughout the experiments. Engine performance parameters, including Brake Power, Brake Torque, Brake Specific Fuel Consumption and exhaust emissions – including NOx and CO, – were tested at engine speeds between 1200 and 2600 rpm. It is seen that HHO enriched CME has better results compared to pure hydrogen enrichment to CME. An average improvement of 4.3% with HHO enriched CME20 was found compared to diesel fuel results while pure hydrogen enriched CME20 fuel resulted with an average increase of 2.6%. Also, it was found that the addition of pure hydrogen to CME had a positive effect on exhaust gas emissions compared to that adding HHO. The effects of both enriched fuels on the engine performance were minimal compared to that of diesel fuel. However, the improvements on exhaust gas emissions were significant.     

Characterisation and effect of using waste plastic oil and diesel fuel blends in compression ignition engine

Plastics have now become indispensable materials in the modern world and application in the industrial field is continually increasing. The properties of the oil derived from waste plastics were analyzed and found that it has properties similar to that of diesel. Waste plastic oil (WPO) was tested as a fuel in a D.I. diesel engine and its performance characteristics were analysed and compared with diesel fuel (DF) operation. It is observed that the engine could operate with 100% waste plastic oil and can be used as fuel in diesel engines. Oxides of nitrogen (NO_x) was higher by about 25% and carbon monoxide (CO) increased by 5% for waste plastic oil operation compared to diesel fuel (DF) operation. Hydrocarbon was higher by about 15%. Smoke increased by 40% at full load with waste plastic oil compared to DF. Engine fueled with waste plastic oil exhibits higher thermal efficiency upto 80% of the full load and the exhaust gas temperature was higher at all loads compared to DF operation.     

Experimental investigation on the combustion process in a spark ignition optically accessible engine fueled with methane/hydrogen blends

The combustion process of a four-stroke optically accessible single cylinder Port Fuel Injection spark ignition (PFI SI) engine was experimentally investigated. It was fueled with two methane/hydrogen blends. The in-cylinder pressure and the related data were analyzed as indicators of the combustion quality. 2D-digital imaging measurements were performed to evaluate the flame propagation. UV–visible spectroscopy allows to characterize the combustion by means of the detection of OH* and CH*. The exhaust was characterized using conventional analyzers. For the methane/hydrogen blends the indicated data suggests an increase of the thermal efficiency and a decrease of the combustion duration with the increase of the hydrogen fraction. The optical results highlight a more homogeneous mixture that increases the combustion reaction rate and provides a more uniform and rapid flame propagation. On the other hand, high NO_x emissions were measured likely because of the higher combustion temperature due to hydrogen addition.     

Artificial Neural Network modeling of a hydrogen dual fueled diesel engine characteristics: An experiment approach

The rapid growth of vehicular pollution; mostly running on the diesel engine, emissions emerging are the concerns of the day. Owing to clean burn characteristics features, Hydrogen (H₂) as a fuel is the paradigm of the researcher. Extensive research presented in the literature on H₂ dual fueled diesel engine reveals, the significant role of H₂ in reducing emissions and enhancing the performance of a dual fueled diesel engine. With meager qualitative experiment data, the feasibility to develop an efficient Artificial Neural Network (ANN) model is investigated, the developed model can be utilized as a tool to investigate the H₂ dual fueled diesel engine further. In the process of developing an ANN model, engine load and H₂ flow rate are varied to register performance and emission characteristics. The creditability of the experiment is ascertained with uncertainty analysis of measurable and computed parameters. Leave-out-one method is adopted with 16 data sets; seven training algorithms are explored with eight transfer function combinations to evolve a competent ANN model. The efficacy of the developed model is adjudged with standard benchmark statistic indices. ANN model trained with Broyden, Fletcher, Goldfarb, & Shanno (BFGS) quasi-Newton backpropagation (trainbfg) stand out the best among other algorithms with regression coefficient ranging between 0.9869 and 0.9996.     

Experimental and numerical investigation of effects of CNG and gasoline fuels on engine performance and emissions in a dual sequential spark ignition engine

Compared to widening usage of CNG in commercial gasoline engines, insufficient but increasing number of studies have appeared in open literature during last decades while engine characteristics need to be quantified in exact numbers for each specific fuel converted engine. In this study, a dual sequential spark ignition engine (Honda L13A4 i-DSI) is tested separately either with gasoline or CNG at wide open throttle. This specific engine has unique features of dual sequential ignition with variable timing, asymmetrical combustion chamber, and diagonally positioned dual spark-plug. Thus, the engine led some important engine technologies of VTEC and VVT. Tests are performed by varying the engine speed from 1500 rpm to 4000 rpm with an increment of 500 rpm. The engine’s maximum torque speed of 2800 rpm is also tested. For gasoline and CNG fuels, engine performance (brake torque, brake power, brake specific fuel consumption, brake mean effective pressure), emissions (O₂, CO₂, CO, HC, NO_x, and lambda), and the exhaust gas temperature are evaluated. In addition, numerical engine analyses are performed by constructing a 1-D model for the entire test rig and the engine by using Ricardo-Wave software. In the 1-D engine model, same test parameters are analyzed, and same test outputs are calculated. Thus, the test and the 1-D engine model are employed to quantify the effects of gasoline and CNG fuels on the engine performance and emissions for a unique engine. In general, all test and model results show similar and close trends. Results for the tested commercial engine show that CNG operation decreases the brake torque (12.7%), the brake power (12.4%), the brake mean effective pressure (12.8%), the brake specific fuel consumption (16.5%), the CO₂ emission (12.1%), the CO emission (89.7%). The HC emission for CNG is much lower than gasoline. The O₂ emission for CNG is approximately 55.4% higher than gasoline. The NO_x emission for CNG at high speeds is higher than gasoline. The variation percentages are the averages of the considered speed range from 1500 rpm to 4000 rpm.     

An experimental study of combustion and emissions in a spark-ignition engine fueled with coal-bed gas

Coal-bed gas has been considered an attractive alternative fuel for internal combustion engines due to its abundant source and low emissions. In the present study, a combustion system with a swirl chamber has been developed for a spark-ignition engine using coal-bed gas. Detailed experiments have been carried out to investigate the combustion and emission characteristics of the engine operating with three different grades of coal-bed gas. The results have shown that this combustion system allows satisfactory operation of the engine with a wide range of methane content in the supplied coal-bed gas. For all tested conditions, the CO emission has a maximum value of 0.062%, and the HC emission is less than 380 ppm. The NO emission increases with the engine load but is less than 1800 ppm, demonstrating a great advantage of coal-bed gas as a relatively clean engine fuel.