Effect of the turbulence intensity on knocking tendency in a SI engine with high compression ratio using biogas and blends with natural gas,propane and hydrogen

This research presents the test results carried out in a diesel engine converted to spark ignition (SI) using gaseous fuels, applying a geometry change of the pistons combustion chamber (GCPCC) to increase the turbulence intensity during the combustion process; with similar compression ratio (CR) of the original diesel engine; the increase in turbulence intensity was planned to rise turbulent flame speed of biogas, to compensate its low laminar flame speed. The research present the test to evaluate the effect of increase turbulence intensity on knocking tendency; using fuel blends of biogas with natural gas, propane and hydrogen; for each fuel blend the maximum output power was measured just into the knocking threshold before and after GCPCC; spark timing (ST) was adjusted for optimum generating efficiency at the knocking threshold. Turbulence intensity with GCPCC was estimated using Fluent 13, with 3D Combustion Fluid Dynamics (CFD) numerical simulations; 12 combustion chamber geometries were simulated in motoring conditions; the selected geometry had the greatest simulated turbulent kinetic energy (TKE) and Reynolds number (Re) during combustion. The increased turbulence intensity was measured indirectly through the periods of combustion duration to mass fraction burn 0–5%, 0–50% and 0–90%; for almost all the fuel blends the increased turbulence intensity of the engine, increased the knocking tendency requiring to reduce the maximum output power to keep engine operation just into the knocking threshold. Biogas was the only fuel without power derating by the conditions of higher pressure and higher turbulence during combustion by GCPCC and improve its generating efficiency. Peak pressure, heat release rate, mean effective pressure and exhaust temperature were lower after GCPCC. Tests results indicated that knocking tendency was increased because of the higher turbulent flame speed; fuel blends with high laminar flame speed and low methane number (MN) had higher knocking tendency and lower output power.     

Effect of equivalence ratio on knocking tendency in spark ignition engines fueled with fuel blends of biogas,natural gas,propane and hydrogen

This research evaluates the effect of the equivalence ratio on knocking tendency in two Spark Ignition (SI) engines fueled with gaseous fuels. A Lister Petter TR2 Diesel engine (TR2) converted to SI was used to evaluate the equivalence ratio effect when the engine was fueled with fuel blends of biogas, natural gas, propane, and hydrogen. A Cooperative Fuel Research (CFR) engine was used to study the effect of equivalence ratio on the Critical Compression Ratio (CCR) which is a metric to evaluate the knocking tendency of gaseous fuels. In both engines, the tests were conducted using the knocking threshold as the engine limit operation to quantify the effect of the equivalence ratio on knocking tendency. Experimental results in the CFR engine revealed that a lean mixture reduces the knocking tendency allowing to operate the CFR engine at higher CCR. In contrast, the effect of the equivalence ratio on the knocking tendency in the TR2 engine was different since leaner mixtures increased the engine knocking tendency. This tendency was caused by the increase in the % throttle which increased the mixture pressure at the end of the compression stroke. The high knocking tendency to lean mixtures forces to reduce the output power to find the knocking threshold for all fuel blends.     

Flexible syngas-biogas-hydrogen fueling spark-ignition engine behaviors with optimized fuel compositions and control parameters

This paper presents the results research on the optimal fuel compositions and the control parameters of the spark ignition engine fueled with syngas-biogas-hydrogen for the purpose of setting up a flexible electronic control unit for the engine working in a solar-biomass hybrid renewable energy system. In syngas-biogas-hydrogen mixture, the optimal content of hydrogen and biogas is 20% and 30%, respectively. Exceeding these thresholds, the improvement of engine performance is moderate, but the pollution emission increases strongly. The optimal advanced ignition angle is 38°CA, 24°CA, and 18°CA for syngas, biogas, and hydrogen, respectively. With the same content of hydrogen or biogas in the mixture with syngas, the advanced ignition angle of the hydrogen-syngas blend is less than that of the syngas-biogas blend by about 4°CA at the engine speed of 3000 rpm. The derating power of the engine is 30% and 23% as switching from the hydrogen and biogas fueling mode to the syngas fueling mode, respectively. However, NO_x emission of the engine increase from 200 ppm (for syngas) to 2800 ppm (for biogas) and to over 6000 ppm (for hydrogen). The optimal advanced ignition angle, the optimal equivalence ratio of the syngas-biogas-hydrogen fuel mixture vary within the limits of the respective values for syngas and hydrogen. To improve the engine efficiency and reduce pollutant emissions, the loading control system of the engine should prioritize the adjustment of the fuel flow and then the adjustment of the air-fuel mixture flow.     

Experimental study of combustion performances and emissions of a spark ignition cogeneration engine operating in lean conditions using different fuels

This work presents an experimental study describing a six-cylinder spark ignition engine running with a lean equivalence ratio, high compression ratio, ignition delay and used in a cogeneration system (heat and electricity production). Three types of fuels; natural gas, pure methane and methane/hydrogen blend (85% CH₄ and 15% H₂ by volume), were used for comparison purposes. Each fuel has been investigated at 1500 rpm and for various engine loads fixed by electrical power output conditions. CO, CO₂, HC, and NOx emissions values, and exhaust gas temperature were measured. The effect of fuel composition on engine characteristics has been studied. The results show, that the hydrogen addition increased HC emissions (around 18%), as well as performance, whilst it reduced NO_x (around 31%), exhaust gas temperature, CO and CO₂.     

An experimental study on performance,emission and combustion parameters of hydrogen fueled spark ignition engine with the timed manifold injection system

In the present study, a single cylinder spark ignition (SI) engine is modified to operate with hydrogen gas with ECU (Electronic Controlled Unit) operated timely manifold injection system. Performance, emission and combustion parameters are studied at MBT (Maximum Brake Torque) spark timing with WOT (Wide Open Throttle) position. All trials are performed in the speed range of 1100 rpm–1800 rpm. Baseline observations are recorded with gasoline for comparison purpose. Results have shown that maximum brake power is reduced by 19.06% and peak brake thermal efficiency is increased by 3.16% in the case of hydrogen operation. Reduction in NO_x emission is observed for hydrogen at higher engine speed. The maximum net heat release rate is two times higher and the peak cylinder pressure is 1.36 times higher for hydrogen as compared to gasoline at the engine speed of 1400 rpm.     

Performance and emission characteristics of a SI engine fueled by low calorific biogas blended with hydrogen

In this study, an experimental investigation on a naturally aspirated (NA), 8-L spark ignition engine fueled by biogas with various methane concentrations - which we called the N₂ dilution test - was performed in terms of its thermal efficiency, combustion characteristics and emissions. The engine was operated at a constant engine rotational speed of 1800 rpm under a 60 kW power output condition and simulated biogas was employed to realize a wide range of changes in heating value and gas composition. The N₂ dilution test results show that an increase of inert gas in biogas was beneficial to thermal efficiency enhancement and NO_x emission reduction, while exacerbating THC emissions and cyclic variations. Then, as a way to achieve stable combustion for the lowest quality biogas, H₂ addition tests were carried out in various excess air ratios. H₂ fractions ranging from 5 to 30% were blended to the biogas and the effects of hydrogen addition on engine behavior were evaluated. The engine test results indicated that the addition of hydrogen improved in-cylinder combustion characteristics, extending lean operating limit as well as reducing THC emissions while elevating NO_x generation. In terms of efficiency, however, a competition between enhanced combustion stability and increased cooling energy loss was observed with a rise in H₂ concentration, maximizing engine efficiency at 5-10% H₂ concentration. Moreover, based on the peak efficiency operating point, a set of optimum operating conditions for minimum emissions with the least amount of efficiency loss was suggested in terms of excess air ratio, spark ignition timing, and hydrogen addition rate as one of the main results.     

Performance evaluation of a constant speed IC engine on CNG,methane enriched biogas and biogas

This paper presents the performance results of a 5.9 kW stationary diesel engine which was converted into spark ignition mode and run on compressed natural gas (CNG), methane enriched biogas (Bio-CNG) and biogas produced from biomethanation of jatropha and pongamia oil seed cakes. The performance of the engine with 12.65 compression ratio was evaluated at 30°, 35° and 40° ignition advance of TDC. The maximum brake power produced by the engine was found at ignition advance of 35° TDC for all the tested fuels. In comparison to diesel as original fuel, the power deteriorations of the engine was observed to be 31.8%, 35.6% and 46.3% on compressed natural gas, methane enriched biogas and raw biogas, respectively, due to its conversion from CI to SI mode. The methane enriched biogas showed almost similar engine performance as compared to compressed natural gas in terms of brake power output, specific gas consumption and thermal efficiency.     

Effects of EGR on performance of engines with spark gap projection and fueled by biogas–hydrogen blends

In this study, the effects of exhaust gas recirculation (EGR) on the behavior of a spark ignition engine fueled by hydrogen-blended low-calorific biogas were investigated, and its performance and emission characteristics were compared with those of the lean burn engine investigated in our previous work. The engine was operated at a constant rotational speed of 1800 rpm under a 60 kW power output condition, and a simulated biogas containing H₂ was used to realize a wide range of gas compositions. The engine test results demonstrate that when less than 20% H₂ was added to the biogas, the EGR operations had inferior fuel economy to the lean burn technique. However, when the H₂ blending ratio was increased, the EGR method achieved higher engine performance with lower NO_x emissions than the legal standard. Analyses of the O₂ fraction and thermal capacity variations of the inlet charge also indicated that a dilution (O₂ replacement) effect rather than a thermal effect was the dominant factor when EGR was introduced in a low-calorific biogas engine. Subsequently, in order to improve the engine efficiency as well as combustion characteristics, the spark gap was projected further into the combustion chamber with EGR engine operations. The engine test results show that repositioning the discharge location improved the thermal efficiency, and the maximum tolerable EGR rate increased because of spatial advantages such as relatively short flame propagation lengths and high electrode temperatures.     

Availability analysis of a coke oven gas fueled spark ignition engine

The current work investigates a coke oven gas fueled spark ignition (SI) engine from the perspective of the first and second laws in order to understand the energy conversion performance of fuels and achieve highly efficient utilization. A detailed energy and exergy analysis is applied to a quasi-dimensional two-zone spark ignition engine model which combines turbulence flame propagation speed model at 1500 rpm by changing gas fuel types, compression ratio, load and ignition timing. It was found that the irreversibility of methane is the maximum and that of syngas is the minimum among the three different fuels. The irreversibility in the combustion process of a coke oven gas fueled SI engine is reduced when the compression ratio or the throttle valve opening angle is increased and the ignition timing is delayed. Increasing the compression ratio and delaying the ignition timing can improve the first and second law efficiency and reduce the brake specific fuel consumption (BSFC). The power performance and fuel economy are good and the energy is also used effectively when the compression ratio is 11, the throttle angle is 90% and the ignition time is ?10° CA ATDC respectively.     

A comparison of the performance analysis of the spark ignition engine fuelled with ethanol–iso-octane and methanol–iso-octane fuel blends

In this research, the effects of unleaded iso-octane (base fuel), iso-octane–ethanol blend (E20) and iso-octane–methanol blend (M20) on engine performance were investigated experimentally in a single-cylinder four-stroke spark-ignition engine. The tests were performed by varying the throttle position and engine speed at a constant load of 8 kg. The engine speed was varied from 1200 to 1750 rpm, with changing the throttle position. The results showed that ethanol and methanol addition to unleaded iso-octane increases the engine torque, power and brake-specific fuel consumption (BSFC) in comparison to base fuel. The results also showed that exhaust temperature increases with the increase in engine speed. The thermal efficiency varies from 14.3% to 35.9% for iso-octane, 20.1–30.59% for E20 and (17.64–27.46%) for M20 fuel. It was also found that the volumetric efficiency of M20 and E20 fuels was higher than that of iso-octane in all speed ranges.     

Experimental study of a single-cylinder engine fueled with natural gas–hydrogen mixtures

The objective of this study is to evaluate the power, efficiency and emissions of an electronic-controlled single-cylinder engine fueled with pure natural gas and natural gas–hydrogen blends, respectively. Replacing the nature gas with hydrogen/methane blend fuels was found to have a significant influence on engine performance. The effects of excess air ratio and spark timing were discussed. The results show that under certain engine conditions the maximum cylinder gas pressure, maximum heat release rate increased with the increase of hydrogen fraction. The increase of hydrogen fraction in the blends contributed to the increase of NO_x and the decrease of HC and CO. The brake specific fuel consumption decreased with the increase of hydrogen fraction. Using HCNG at relatively leaner fuel–air mixtures and retarded spark timing totally improved the engine emissions without incurring the performance penalty.     

Generating efficiency and emissions of a spark-ignition gas engine generator fuelled with biogas–hydrogen blends

We investigated the generating efficiency and pollutant emissions of a four-stroke spark-ignition gas engine generator operating on biogas–hydrogen blends of varying excess air ratios and hydrogen concentrations. Experiments were carried out at a constant engine speed of 1200 rpm and a constant electric power output of 10 kW. The experimental results showed that the peak values of generating efficiency, maximum cylinder pressure, and NO_x emissions were elevated at an excess air ratio of around 1.2 as the hydrogen concentration was increased. CO₂ emissions decreased as the excess air ratio and hydrogen concentration increased, due to lean-burn conditions and hydrogen combustion. An efficiency per NO_x emissions ratio (EPN) was defined to consider the relationship between the generating efficiency and NO_x emissions. A maximum EPN value of 0.7502 was obtained with a hydrogen concentration of 15%, for an excess air ratio of 2.0. At this EPN value, the NO_x and CO₂ emissions were 39 ppm and 1678.32 g/kWh, respectively, and the generating efficiency was 29.26%. These results demonstrated that the addition of hydrogen to biogas enabled the effective generation of electricity using a gas engine generator through lean-burn combustion.     

An experimental analysis of hydrogen enrichment on combustion characteristics of a gasoline Wankel engine at full load and lean burn regime

In this paper, a gasoline Wankel engine was modified and equipped with self-developed hybrid electronic control unit to experimentally investigate the effect of hydrogen-enrichment level on combustion characteristics of a gasoline Wankel engine at wild open throttle position and lean burn regime. Testing were carried out under constant engine speed of 3000 rpm and the lean operating limit of the original gasoline engine. The spark timing was set at 15 °BTDC. The hydrogen energy fraction in the intake was gradually increased from 0% to 10%. The results showed that hydrogen enrichment was effective on improving the combustion process through the shortened of the flame development and the flame propagation periods, advancing the central heat release, increasing the HRRmax and reducing the cyclic variation proportionally to the amount of hydrogen added to the air fuel mixture. Furthermore, increasing hydrogen fraction in the intake improves the engine economy by reducing the cooling loss.     

The effect of hydrogen on the performance and emissions of an SI engine having a high compression ratio fuelled by compressed natural gas

The aim of this paper is investigation of the effect of hydrogen on engine performance and emissions characteristics of an SI engine, having a high compression ratio, fuelled by HCNG (hydrogen enriched compressed natural gas) blend. The experiments were carried out at 1500, 2000 and 2500 rpm under full load conditions of a modified Isuzu 3.9 L engine, having a compression ratio of 12.5. The engine brake power, brake thermal efficiency, combustion analysis and emissions parameters were realized at 5, 10 15 and 20 deg. CA BTDC (crank angle before top dead center) ignition timings and in excess air ratios of 0.9–1.3 fuelled by hydrogen enriched compressed natural gas (100/0, 95/5, 90/10 and 80/20 of % natural gas/hydrogen).The experimental results showed that the maximum power values were generally obtained with HCNG5 (5% hydrogen in natural gas) fuel. The optimum ignition timing that was obtained according to the maximum brake torque was retarded by the addition of hydrogen to CNG (compressed natural gas), while it was advanced by increasing the engine speed. Furthermore, it was observed that the BTE (brake thermal efficiency) generally declined with the hydrogen addition to compressed natural gas and increasing the engine speed. Additionally, the curves of cylinder pressure and ROHR (rate of heat release values) generally closed to top dead center with the increasing of the hydrogen fraction in the blend and a decreasing engine speed. The hydrocarbon and carbon monoxide emissions generally obtained were lower than the Euro-5 and Euro-6 standards.     

Investigation on the mixture formation,combustion characteristics and performance of a Diesel engine fueled with Diesel,Biodiesel B20 and hydrogen addition

An experimental and numerical study was performed to investigate the impact of Biodiesel B20 (blends 20% Rapeseed methyl ester with 80 % Diesel volumetric fraction) and different energetic fractions of hydrogen content (between 0 and 5%) on the mixture formation, combustion characteristics, engine performance and pollutant emissions formation. Experiments were carried out on a tractor Diesel engine, four-cylinders, four-stroke, 50 kW/2400 rpm, and direct injection. Simulations were conducted using the AVL codes (HYDSIM and BOOST 2013). Simulation results were validated against experimental data, by comparing the inline pressure, needle lift, in-cylinder pressure curves for Biodiesel B20 and pure Diesel fuels at 1400 rpm and 2400 rpm, respectively, under full load operating conditions. Good agreement with a maximum of 2.5% relative deviation on the peak results revealed that overall operation conditions Biodiesel B20 provides lower engine performance, efficiency, and emissions except the NOx which are slightly increased. The Biodiesel B20 has shorter ignition delay. By hydrogen addition to B20 with aspiration of the intake air flow the CO emissions, smoke, and total unburned hydrocarbon emissions THC decreased, while the NOx kept the same increasing trend for 1400 rpm and has not quite apparent trend for 2400 rpm. The enrichment by hydrogen of Diesel and B20 fuels has not a significant effect on ignition delay.     

Crude palm oil fuel for diesel-engines: Experimental and ANN simulation approaches

In the current work, the effect of using CPO (crude palm oil)-OD (ordinary diesel) blends as fuel on the performance of CI (compression ignition) engine is studied. Three different blends of CPO-OD (25%, 50% and 75%) were investigated using direct-injection, stationary diesel engine. The CPO-OD blends were preheated to about 60 °C before the injection to reduce the viscosity of the blends. The experiments were conducted at variable engine speeds (1000 rpm through 3000 rpm) under fixed throttle opening. The results revealed that the CPO-OD exhibited higher torque and power output at engine speeds lower than 2000 rpm, while the BSFC (brake specific fuel consumption) was found to be higher than the OD at the same engine speeds. CPO enhanced the BSFC at higher engine speeds (above 2000 rpm). The CPO-OD blends exhibited lower emissions of NO_x and higher emission of CO compared to the OD.     

The effect of engine speed and cylinder-to-cylinder variations on backfire in a hydrogen-fueled internal combustion engine

The port-injection-type hydrogen engine is advantaged in that hydrogen gas is injected into the intake pipe through a low-pressure fuel injector, and the mixing period with air is sufficient to produce uniform mixing, improving the thermal efficiency. A drawback is that the flame backfires in the intake manifold, reducing the engine output because the amount of intake air is reduced, owing to the large volume of hydrogen. Here, the backfire mechanism as a part of the development of full-load output capability is investigated, and a 2.4-liter reciprocating gasoline engine is modified to a hydrogen engine with a hydrogen supply system. To secure the stability and output performance of the hydrogen engine, the excess air ratio was controlled with a universal engine control unit.The torque, excess air ratio, hydrogen fuel, and intake air flow rate changes in time were compared under low- and high-engine speed conditions with a wide-open throttle. The excess air ratio depends on the change in the fuel amount when the throttle is completely opened, and excess air ratio increase leads to fuel/air-mixture dilution by the surplus air in the cylinder. As the engine speed increases, the maximum torque decreases because the excess air ratio continues to increase due to the occurrence of the backfire. The exhaust gas temperature also increases, except at an engine speed of 6000 rpm. Furthermore, the increase in exhaust gas temperature affects the backfire occurrence. At 2000 rpm, under low-speed and wide-open throttle conditions, backfire first occurs in the No. 4 cylinder because the mixture is heated by the relatively high port temperature. In contrast, at 6000 rpm, under high-speed and wide-open throttle conditions, the backfire starts at the No. 2 cylinder first because of a higher exhaust gas temperature, resulting in a lower excess air ratio in cylinders 2 and 3, located at the center of the engine.     

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.     

Power output characteristics of hydrogen-natural gas blend fuel engine at different compression ratios

Potential and knocking characteristics of a hydrogen-natural gas blend (HCNG) engine with a high compression ratio were examined from a commercial viewpoint since lean combustion with HCNG under a wide-open throttle (WOT) condition requires a high-charging-capacity turbocharger. Supercharging of intake air to extend the lean limit was investigated for a turbocharged, heavy-duty natural gas-fueled engine. Effects of compression ratio changes on fuel economy were assessed in terms of thermal efficiency and torque characteristics. Extension of the lean limit to an excess air ratio of 1.8 for an HCNG engine under WOT conditions is realizable using a supplementary supercharging system. Thermal efficiency improvement at high compression ratios is reduced under relatively rich mixture conditions because spark timing is retarded to avoid knocking. The excess air ratio corresponding to maximum thermal efficiency decreases to 1.6 for an HCNG engine due to the decrease in exhaust gas energy for intake-air charging.     

Effect of hydrogen nanobubble addition on combustion characteristics of gasoline engine

Hydrogen is an attractive energy source for improving gasoline engine performance. In this paper, a new hydrogen nanobubble gasoline blend is introduced, and the influence of hydrogen nanobubble on the combustion characteristics of a gasoline engine is experimentally investigated. The test was performed at a constant engine speed of 2000 rpm, and engine load of 40, 60, and 80%. The air-to-fuel equivalence ratio (λ) was adjusted to the stoichiometric (λ = 1), for both gasoline, and the hydrogen nanobubble gasoline blend. The results show that the mean diameter and concentration of hydrogen nanobubble in the gasoline blend are 149 nm and about 11.35 × 10⁸ particles/ml, respectively. The engine test results show that the power of a gasoline engine with hydrogen nanobubble gasoline blend was improved to 4.0% (27.00 kW), in comparison with conventional gasoline (25.96 kW), at the engine load of 40%. Also, the brake specific fuel consumption (BSFC) was improved, from 291.10 g/kWh for the conventional gasoline, to 269.48 g/kWh for the hydrogen nanobubble gasoline blend, at the engine load of 40%.