Experimental investigation on effect of misfire and postfire on backfire in a hydrogen fuelled automotive spark ignition engine

This study investigates the effect of misfire and postfire on backfire in a hydrogen-fuelled automotive spark ignition engine. Backfire is a preignition phenomenon and the flame propagates toward the engine's intake manifold during the suction stroke. Postfire is a post-ignition phenomenon occurring in the exhaust manifold during the exhaust stroke and the flame propagates towards the exhaust manifold or backflow to the combustion chamber or combined both. Misfire occurs when cranking the engine (starting), fouled spark plug, and unoptimized spark timing. Several misfire cycles lead to an increase in the accumulation of unburnt hydrogen-air charge inside the cylinder and 13% hydrogen leaves the exhaust manifold resulting in postfire occurrence in a subsequent cycle. The postfire in the current cycle acting as an external ignition source for the preignition of the accumulated hydrogen-air charge results in backfire in the immediate next cycle. The misfire, postfire and backfire stall the engine operation due to a drop in indicated mean effective pressure. The experimental data indicates the backfire limiting equivalence ratio (BLER) should decrease with an increase in the engine speed as the equivalence ratio varies from 0.91 at 2000 rpm to 0.4 at 4900 rpm. As too advancement of spark timing increases the probability of misfire leading to postfire and backfire, the engine must be operated at backfire limiting spark timing to avoid misfire, postfire, and backfire occurrence. An important point emerged from this study that misfire without postfire does not lead to backfire occurrence. Physical mechanisms and mitigative measures for misfire, postfire and backfire are discussed in detail.     

Experimental study of the effects of excess air ratio on combustion and emission characteristics of the hydrogen-fueled rotary engine

To investigate the property of the promising and eco-friendly hydrogen-fueled rotary engine, the effect of excess air ratio on the combustion and emission characteristic of it was explored by experiment. The test was conducted under 1500 rpm and 5 CAD ADTC ignition timing. The test results demonstrated that with the decrease of excess air ratio from 2 to 0.85, the thermal efficiency of the hydrogen-fueled rotary engine increases first and then decreases. Besides, increasing MAP is beneficial to improve thermal efficiency. Among the tested condition, the highest brake thermal efficiency is realized when the rotary engine operates at 1.4 excess air ratio and 88 kPa MAP, about 18.34%. And the excellent HC and NO emissions can be obtained at the highest efficiency point. Besides, with the decrease of excess air ratio and the increase of load, the stability and flame development period gradually decrease. With a decreased excess air ratio, the flame propagation period decrease first and then increases, whereas work capacity and thermal efficiency increase first and then decrease. For NO emission, it will increase sharply near the equivalent ratio and gradually decrease after rich combustion. Also, according to the analytical model, it is found that the power performance of the rotary engine depends on the trade-off relationship of in-cylinder pressure and its angle of action.     

Monitoring of hydrogen-fueled engine backfires using dual manifold absolute pressure sensors

The application of hydrogen in internal combustion engines (ICE) has attracted widespread attention. However, due to the low ignition energy, high flame propagation speed, and wide combustible range of hydrogen, it is easy to cause abnormal combustion phenomena such as backfire in the port fuel injected (PFI) hydrogen-fueled engine. When a backfire occurs, the combustible mixture burns in the intake, resulting in a decrease in the volumetric efficiency of the engine, which may cause it to misfire or shut down in severe cases. Fast and accurate detection of backfire events is essential to take targeted control measures. In this research, a backfire detection system based on dual intake manifold absolute pressure (MAP) sensors were designed, with two MAP sensors installed on the intake manifolds of the first and fourth cylinders, and four gas injectors were installed on the intake manifold to convert the gasoline ICE into a hydrogen-fueled ICE. During the experiment, the engine speed was stabilized at 1000 rpm, the throttle valve was fully opened, and the intake pressure was maintained at 100 kPa.The test results show that the system can accurately determine the location and intensity of backfire occurrence. This method provides a basis for precise control of backfiring.     

A study on the effect of qualitative control coupling variable engine speed on the hydrogen-fueled Wankel rotary engine at wide-open throttle

Hydrogen-fueled Wankel rotary engine, with few available research currently, has excellent power and emission characteristics, however, with lower efficiency. With increasing attention to low-carbon emission, it is of great significance to explore methods to improve the efficiency of hydrogen-fueled Wankel rotary engines. This work aims to study the effect of qualitative control coupling variable engine speeds at the wide-open throttle on the power control. The comparative effect of qualitative control coupling engine speeds from 1000 r/min to 1500 r/min under the wide-open throttle and quantitative control at 1500 r/min on the combustion and emission characteristic of hydrogen-fueled Wankel rotary engine is investigated. The results show that compared with quantitative control, qualitative control coupling variable engine speed can achieve excellent performance. The brake thermal efficiency can be maximally increased by 43.5%, an absolute increase of 6.22%, as well the volumetric efficiency with a maximal 105% improvement. The thermal load and risk of knock can be greatly reduced. Moreover, NO emission also can be reduced by more than an order of magnitude or even by zero. Although there is an increase in cyclic variation, the value is no more than 4%. In addition, qualitative control coupling variable engine speed allows flexible matching of appropriate engine speed and excess air ratio based on the actual requirements of efficiency, stability, durability and emission.     

Cycle variations in a hydrogen internal combustion engine

The cycle variation characteristics of a port fuel injection hydrogen internal combustion engine (PFI-HICE) have been extensively investigated. The covariance of indicated mean effective pressure (COV_imep) is the best parameter for evaluating the cycle variations in the PFI-HICE. COV_imep decreases as fuel–air ratio increases from 1000 to 5500 rpm, and engine speed minimally affects COV_imep. The effect of ignition advance angle on COV_imep is determined by fuel–air ratio. The ignition advance angles that correspond to the minimum COV_imep of the PFI-HICE decrease as fuel–air ratio increases. The effect of ignition advance angle on COV_imep diminishes as fuel–air ratio increases. The COV_imep of the PFI-HICE rapidly decreases as throttle increases when the throttle is less than 20%. Injection timing only slightly affects COV_imep under high-speed conditions, and COV_imep increases when hydrogen is injected in intake periods under low-speed conditions. These results indicate that studying COV_imep improves the stability of PFI-HICEs.     

Diagnosis and control of abnormal combustion of hydrogen internal combustion engine based on the hydrogen injection parameters

In order to improve the limitation of evaluating the abnormal combustion problem of hydrogen internal combustion engine by single index, the abnormal combustion risk coefficient is proposed and defined based on AHP(Analytic Hierarchy Process)-entropy method. The abnormal combustion risk of PFI hydrogen internal combustion engine is comprehensively evaluated from multiple indexes such as the uniformity coefficient of the mixture, the temperature of the hot area, the maximum temperature rise rate, the residual amount of hydrogen in the intake port and the cylinder temperature at the end of the exhaust. The influence of hydrogen injection parameters on abnormal combustion was explored. The results show that the temperature and the maximum temperature rise rate in the hot area decrease first and then increase with the increase of hydrogen injection angle and hydrogen injection flow rate. Although large hydrogen injection angle and hydrogen injection flow rate can reduce the cylinder temperature at the end of exhaust, they will increase the residual hydrogen amount in the intake port. Appropriate hydrogen injection angle and hydrogen injection flow scheme can ensure that all parameters are at a better level, so that the risk coefficient of abnormal combustion decreases by 2.1%–5.5%, and the possibility of abnormal combustion is reduced.     

The hydrogen-fueled internal combustion engine: a technical review

A review is given of contemporary research on the hydrogen-fueled internal combustion engine. The emphasis is on light- to medium-duty engine research. We first describe hydrogen-engine fundamentals by examining the engine-specific properties of hydrogen and surveying the existing literature. Here it will be shown that, due to low volumetric efficiencies and frequent preignition combustion events, the power densities of premixed or port-fuel-injected hydrogen engines are diminished relative to gasoline-fueled engines. Significant progress has been made in the development of advanced hydrogen engines with improved power densities. We discuss several examples and their salient features. Finally, we consider the overall progress made and provide suggestions for future work.     

A comparative study on effects of homogeneous or stratified hydrogen on combustion and emissions of a gasoline/hydrogen SI engine

A comparative study on effects of homogeneous or stratified hydrogen on combustion and emissions was presented for a gasoline/hydrogen SI engine. Three kinds of injection modes (gasoline, gasoline plus homogeneous hydrogen and gasoline plus stratified hydrogen) and five excess air ratios were applied at low speed and low load on a dual fuel SI engine with hydrogen direct injection (HDI) and gasoline port injection. The results showed that, with the increase of excess air ratio, the brake thermal efficiency increases firstly then decreases and reaches the highest when the excess air ratio is 1.1. In comparison with pure gasoline, hydrogen addition can make the ignition stable and speed up combustion rate to improve the brake thermal efficiency especially under lean burn condition. Furthermore, it can reduce the CO and HC emissions because of more complete combustion, but produce more NO_X emissions due to the higher combustion temperature. Since, in the gasoline plus stratified hydrogen mode, the hydrogen concentration near the sparking plug is denser than that of homogeneous hydrogen, the ignition is more stable and faster, which further speed up the combustion rate and improve the brake thermal efficiency. In the gasoline plus stratified hydrogen mode, the brake thermal efficiency increases by 0.55%, the flame development duration decreases by 1.0°CA, rapid combustion duration decreases by 1.3°CA and the coefficient of variation (COV) decreases by 9.8% on average than that of homogeneous hydrogen. However, in the gasoline plus stratified hydrogen mode, due to the denser hydrogen concentration near the sparking plug and leaner hydrogen concentration near the wall, the combustion temperature and the wall quenching distance increase, which make the NO_X and HC emissions increase by 14.3% and 12.8% on average than that of homogeneous hydrogen.     

A study on realization of high performance without backfire in a hydrogen-fueled engine with external mixture

In order to grasp the possibility of achieving backfire control, high performance, and low emission in a hydrogen-fueled engine using external mixture injection, the effects of increasing the boosting pressure were analyzed in terms of backfire occurrence, combustion characteristics, and performance enhancement.     

Backfire prediction in a manifold injection hydrogen internal combustion engine

Hydrogen internal combustion engine (H2ICE) easily occur inlet manifold backfire and other abnormal combustion phenomena because of the low ignition energy, wide flammability range and rapid combustion speed of hydrogen. In this paper, the effect of injection timing on mixture formation in a manifold injection H2ICE was studied in various engine speed and equivalence ratio by CFD simulation. It was concluded that H2ICE of manifold injection have an limited injection end timing in order to prevent backfire in the inlet manifold. Finally, the limit of injection end timing of the H2ICE was proposed and validated by engine experiment.     

Experimental investigation on effects of knocking on backfire and its control in a hydrogen fueled spark ignition engine

The experimental study was carried out on a multi-cylinder spark ignition engine fueled with hydrogen for analyzing the effect of knocking on backfire and its control by varying operating parameters. The experimental tests were conducted with constant speed at varied equivalence ratio. The equivalence ratio of 0.82 was identified as backfire occurring equivalence ratio (BOER). The backfire was identified by high pitched sound and rise in in-cylinder pressure during suction stroke. In order to analyze backfire at equivalence ratio of 0.82, the combustion analysis was carried out on cyclic basis. Based on the severity of in-cylinder pressure during suction stroke, the backfire can be divided into two categories namely low intensity backfire (LIB) and high intensity backfire (HIB). From this study, it is observed that there is frequent LIB in hydrogen fueled spark ignition engine during suction stroke, which promotes instable combustion and thus knocking at the end of compression stroke. This knocking creates high temperature sources in the combustion chamber and thus causes HIB to occur in the subsequent cycle. A notable salient point emerged from this study is that combustion with knocking can be linked with backfire as probability of backfire occurrence decreases with reduction in chances of knocking. Retarding spark timing and delaying injection timing of hydrogen were found to reduce the chances of backfire occurrence. The backfire limiting spark timing (BLST) and backfire limiting injection timing (BLIT) were found as 12 ⁰bTDC and 40 ⁰aTDC respectively.     

Engine speed and air-fuel ratio effect on the combustion of methane augmented hydrogen rich syngas in DI SI engine

The main challenge on the fueling of pure hydrogen in the automotive vehicles is the limitation in the hydrogen separation from the product of steam reforming and gasification plants and the storage issues. On the other hand, hydrogen fueling in automotive engines has resulted in uncontrolled combustion. These are some of the factors which motivated for the fueling of raw syngas instead of further chemical or physical processes. However, fueling of syngas alone in the combustion chamber has resulted in decreased power output and increased in brake specific fuel consumption. Methane augmented hydrogen rich syngas was investigated experimentally to observe the behavior of the combustion with the variation of the fuel-air mixture and engine speed of a direct-injection spark-ignition (DI SI) engine. The molar ratio of the high hydrogen syngas is 50% H₂ and 50% CO composition. The amount of methane used for augmentation was 20% (V/V). The compression ratio of 14:1 gas engine operating at full throttle position (the throttle is fully opened) with the start of the injection selected to simulate the partial DI (180° before top dead center (BTDC)). The relative air-fuel ratio (λ) was set at lean mixture condition and the engine speed ranging from 1500 to 2400 revolutions per minute (rpm) with an interval of 300 rpm. The result indicated that coefficient of variation of the indicate mean effective pressure (COV of IMEP) was observed to increase with an increase with λ in all speeds. The durations of the flame development and rapid burning stages of the combustion has increased with an increase in λ. Besides, all the combustion durations are shown to be more sensitive to λ at the lowest speed as compared to the two engine speeds.     

An experimental study on the backfire occurrence and combustion stabilization of high-efficiency hydrogen-fueled free-piston linear power systems

A scavenging method suitable for high-efficiency hydrogen (H₂)-fueled two-stroke free-piston linear power systems as a next-generation alternative engine is experimentally studied, investigating the driving and backfire suppression characteristics of various scavenging methods by using a rapid compression expansion machine. A simple structured loop-scavenging method which was expected to be unfavorable for suppressing backfire in H₂-fueled power systems is more advantageous than the valve-driven scavenging methods when the system performance is evaluated together. For the loop-scavenging method, no backfire is observed at the fuel-equivalence ratio φ ≤ 0.6 when the ignition timing IGT is set for the maximum pressure (MPT) and the backfire limit can be extended to φ = 0.8 if IGT is advanced than MPT, showing the maximum indicated thermal efficiency of 48%. The performance test using a single-type H₂-fueled free-piston linear power system adopting the loop-scavenging successfully demonstrates stable continuous operation with no backfire at φ ≤ 0.8.     

Backfire control and power enhancement of a hydrogen internal combustion engine

Frequent backfire can occur in inlet port fuel injection hydrogen internal combustion engines (HICEs) when the equivalence fuel–air ratio is larger than 0.56, thus limiting further enhancement of engine power. Thus, to control backfire, an inlet port fuel injection HICE test system and a computational fluid dynamics model are established to explore the factors that cause backfire under high loads. The temperature and the concentration of the gas mixture near the intake valves are among the essential factors that result in backfire. Optimizing the timing and pressure of hydrogen injection reduces the concentration distribution of the intake mixture and the temperature of the high-concentration mixture through the inlet valve, thus allowing control of backfire. Controlling backfire enables a HICE to work normally at high equivalence fuel–air ratio (even beyond 1.0). A HICE with optimized hydrogen injection timing and pressure demonstrates significant enhancement of the power output.     

Control of backfire and NOx emission reduction in a hydrogen fueled multi-cylinder spark ignition engine using cooled EGR and water injection strategies

The experimental study was carried out on a constant speed multi-cylinder spark ignition engine fueled with hydrogen. Exhaust gas recirculation (EGR) and water injection techniques were adopted to control combustion anomalies (backfire and knocking) and reduce NOx emission at source level. The experimental tests were conducted on the engine with varied EGR rate (0%–28% by volume) and water to hydrogen ratio (WHR) (0–9.25) at 15 kW load. It was observed from the experiments that both the strategies can control backfire effectively, but water injection can effectively control backfire compared to EGR. The water injection and EGR reduce the probability of backfire occurrence and its propagation due to the increase in the requirement of minimum ignition energy (MIE) of the charge, caused mainly due to charge dilution effect, and reduction in flame speed respectively. The NOx emission was continuously reduced with increase in EGR rate and WHR, but at higher rates (of EGR and WHR), there was an issue of stability of engine operation. It was found from the experimental results that at 25% EGR, there was 57% reduction in NOx emission without drop in brake thermal efficiency whereas, with WHR of 7.5, the NOx emission was reduced by 97% without affecting the efficiency. The salient point emerging from the study is that water injection technique can control backfire with ultra-low (near zero) NOx emission without compromising the performance of the hydrogen fueled spark ignition engine.     

Idle performance of a hydrogen rotary engine at different excess air ratios

Rotary engine has flat chamber and longs for fuel with high flame speed and small quenching distance. Hydrogen has many excellent characteristics that are suitable for the rotary engine. In this paper, the performance of a rotary engine fueled with pure hydrogen at different excess air ratios was experimentally investigated. The investigation was carried out on a single-rotor hydrogen-fueled rotary engine equipped with port fuel injection system. An online electronic control module was used to govern the hydrogen injection duration and excess air ratio. In this study, the engine was operating at the idle speed of 3000 rpm and different excess air ratios varied from 0.993 to 1.283. The test results demonstrated that the fuel energy flow rate of the hydrogen rotary engine and engine stability were reduced with the increase of excess air ratio. When the excess air ratio increased from 0.993 to 1.283, the hydrogen energy flow rate was decreased from 14.91 to 11.55 MJ/h. Both the flame development and propagation periods were increased with excess air ratio. CO emission was negligible, but HC, CO₂ and NOx emissions were still detected due to the evaporation and possible burning of the lubrication-used gasoline, and oxidation reaction of nitrogen of the intake air.     

Fundamental characterization of backfire in a hydrogen fuelled spark ignition engine using CFD and experiments

Backfire, an abnormal combustion phenomenon, in a hydrogen fuelled spark ignition (SI) engine was analyzed using computational fluid dynamics (CFD) and experimental tests. One of the main causes of backfire origin is the presence of any high temperature heat source including hot spot in the combustion chamber of the engine during intake process. A CFD based parametric study was carried out by varying the temperature of hot spot and its location in the combustion chamber of the engine in order to analyze their effects on backfire origin and its propagation in the intake manifold of the engine. The temperature of hot spot was varied from 800 K to till the temperature of backfire occurrence. The minimum temperature of hot spot at which backfire occurred was observed as 950 K and beyond. The probability of backfire occurrence increases with increase in hot spot temperature. The CFD simulations were also carried out by varying the location of hot spot (spark plug tip and exhaust valve) and the results indicate that the location of hot spot does not influence the characteristics of backfire but it affects the timing of its origin. The average backfire velocity is 230 m/s based on the average turbulent flame velocity during backfire propagation in the intake manifold and the value agreed reasonably well with the experimental observations of backfire propagation on the engine with the transparent intake manifold. Backfire propagation is under the category of deflagration based on its velocity (subsonic), and the maximum pressure gradient (<0.3 bar). The backfire phenomenon is characterized into three stages namely ignition delay for backfire, backfire propagation and its termination. The study results provide a better in-depth understanding of backfire origin and its propagation and would be helpful for developing a robust control strategy. Based on this study, it is recommended that the spark plug and exhaust valves of hydrogen fuelled SI engine should be customized in such a way that the temperature of spark plug tip and exhaust valves should not exceed 900 K during suction process in order to eliminate backfire occurrence.     

An investigation on effect of in-cylinder swirl flow on performance,combustion and cyclic variations in hydrogen fuelled spark ignition engine

This study investigates how engine performance, cyclic variations and combustion parameters are affected by swirling flow in hydrogen spark ignition (SI) engine. Swirling flow was produced in the cylinder during the induction stroke by intake port having entry angles of 0°, 10°, 20° and 30°. In addition, tumble angle of 8° was positioned for given entry angles. The engine was operated under lean mixture (ϕ = 0.6) conditions and engine speeds of 1400, 1600 and 1800 rpm. As a result, it was found that swirling flow enhances performance of hydrogen SI engine around 3% when operating engine with entry angle of 20°. The combustion duration and the cyclic variation in hydrogen SI engine can be reduced with optimum swirling flow. The stability of combustion in hydrogen SI engine is mainly dependent on cyclic variations in the flame initiation period and the cyclic variations in this period can be reduced with controlled swirling flow.     

Development of online control system for elimination of backfire in a hydrogen fuelled spark ignition engine

Backfire is one of the major technical issues in a port injection type hydrogen fuelled spark ignition engine. It is an abnormal combustion phenomenon (pre-ignition) that takes place in combustion chamber and intake manifold during suction stroke. The flame propagates toward the upstream of the intake manifold from combustion chamber during backfire and thus can damage the intake and fuel supply systems of the engine, and stall the engine operation. The main cause of backfire could be the presence of any hot spot, lubricating oil particle's traces (HC and CO due to evaporation of the oil) and hot residual exhaust gas present in the combustion chamber during suction stroke which could act as an ignition source for fresh incoming charge. Monitoring the temperatures of the lubricating oil and exhaust gas during engine operation can reduce the probability of backfire. This was achieved by developing an electronic device which delays the injection timing of hydrogen fuel with the inputs of engine oil temperature (T_{lube oil}) and exhaust gas temperature (T_exh). It was observed from the experimental results that the threshold values of T_{lube oil} and T_exh were 85 °C and 540 °C respectively beyond which backfire occurred at equivalence ratio (φ) of 0.82. The developed device works based on the algorithm that retards the hydrogen injection to 40 ⁰aTDC whenever the temperatures (T_{lube oil} and T_exh) reached to the above mentioned values and thus the backfire was controlled. Delaying injection of hydrogen increased the time period at which only air is inducted during the early part of the suction stroke, this allows cooling of the available hot spots in the combustion chamber, hence the probability of backfire would be reduced.     

Effect of excess hydrogen on hydrogen fueled internal combustion engine under full load

Detailed hydrogen-air chemical reaction mechanisms were coupled with three dimension grids of an experimental hydrogen fueled internal combustion engine (HICE) to establish a combustion model based on CONVERGE software. The influence of excess hydrogen coefficient on the combustion and emission characteristics of HICE under full load was studied based on the CFD model. Simulation results showed that excess hydrogen leaded to higher concentration of OH species in flame front, and quicker hydrogen-oxygen reaction and flame propagation speed, which in turn leaded to higher pressure and temperature in cylinder. The rise of pressure and temperature in turn contributed to the increase of indicate power but un-burned hydrogen leaded to decrease of efficiency. NOx, especially NO emissions decreased significantly with excess hydrogen under full load not only because increased of H concentration, and decreased of O and OH concentration, which leaded to reverse reaction of NO formation through thermal NO routes. Low excess hydrogen coefficient can achieve a good trade-off between power and emissions under full load.