Research on optimal control to resolve the contradictions between restricting abnormal combustion and improving power output in hydrogen fueled engines

In this paper, based on experiment result in a hydrogen fueled engine, pre-ignition and transforming process from pre-ignition to backfire of the hydrogen fueled engine was analyzed. Moreover, mechanism of pre-ignition and backfire of hydrogen fueled engines was studied by analyzing chain reaction. The analysis shows that the temperature, pressure and rate of pressure rise have great influence on pre-ignition and backfire. And based on thermodynamic relations of heat release rate, both pre-ignition and backfire were also analyzed. Finally, optimization control model which has multi-variables, multi-objectives and multi-constraints was established. And the simulation was carried out through the genetic algorithm. Results have shown that the excess air ratio and ignition advance angle can be adjusted by weighted coefficients to optimize the power output and restrict the abnormal combustion. Thus, a useful method is shown to resolve the contradictions between restricting the abnormal combustion and improving hydrogen fueled engine’s power output.     

Stoichiometric H2ICEs with water injection

For the most part, gasoline engines operate close to stoichiometry because of the high power density and the easy after treatment through the very well established three-way catalytic converter technology. The lean burn gasoline engine suffers major disadvantages for the after treatment still requiring aggressive research and development to meet future emission standards more than for the lower power density compensated by the better fuel conversion efficiency running lean. Hydrogen engines are usually run ultra-lean to avoid abnormal combustion phenomena and possibly to avoid the emission of nitrogen oxides without the difficult non-stoichiometric after treatment. While the ultra-lean combustion of hydrogen may reduce the formation of NOx within the cylinder but makes the power density very low, the only lean combustion of hydrogen requires after treatment for NOx reduction. The suppression of abnormal combustion in hydrogen engines has been a challenge for the three regimes of abnormal combustion, knock (auto ignition of the end gas region), pre-ignition (uncontrolled ignition induced by a hot spot prior of the spark ignition) and backfire (premature ignition during the intake stroke, which could be seen as an early form of pre-ignition). Direct injection and jet ignition coupled to port water injection are used here to avoid the occurrence of all these abnormal combustion phenomena as well as to control the temperature of gases to turbine in a turbocharged stoichiometric hydrogen engine.     

Experimental study of hydrogen enriched compressed natural gas (HCNG) engine and application of support vector machine (SVM) on prediction of engine performance at specific condition

The effect of excess air ratio (λ) and ignition advance angle (θ_ig) on the combustion and emission characteristics of hydrogen enriched compressed natural gas (HCNG) on a 6-cylinder compressed natural gas (CNG) engine has been experimental studied in an engine test bench, aiming at enriching the sophisticated calibration of HCNG fueled engine and increasing the prediction accuracy of the SVM method on automobile engines. Three different fuel blends were selected for the experiment: 0%, 20% and 40% volumetric hydrogen blend ratios. It is noted that combustion intensity varies with the excess air ratio and the ignition advance angle, so are the emissions. The optimal value of λ or θ_ig has been explored in the specific engine condition. Results show that blending hydrogen can enhance and advance the combustion and stability of CNG engine, and it also has some benefic influence on the emissions such as reducing the CO and CH₄. Meanwhile, a simulation research on forecasting the engine performance by using the support vector machine (SVM) method was conducted in detail. The torque, brake specific fuel consumption and NO_x emission have been selected to characterize the power, economic and emissions of the engine with various HCNG fuels, respectively. It can be seen that the optimal model built by the SVM method can highly describe the relationship of the engine properties and condition parameters, since the value of the complex correlation coefficient is larger than 0.97. Secondly, the prediction performance of the optimal model for torque or BSFC is much better than the case of NO_x. Besides, the optimal model built by the PSO optimization method has the best prediction accuracy, and the accuracy of the model obtained based on the training group with 20% hydrogen blend ratio is the best compared with those of others. The upshots in this article provide experimental support and theoretical basis for the adoption of HCNG fuel on internal combustion engines as well as the application of intelligent algorithmic in the engine calibration technology field.     

热裂解生物质气发动机燃烧特性试验

利用农林废弃物可控热裂解产生的生物质气作为火花点火发动机的燃料,测最火花点火生物质气发动机的示功图,分析了生物质气的燃烧放热特性.试验结果表明:发动机怠速点火性能较好,小功率时放热速度较慢,大功率时燃烧速度较快,燃烧较充分;火焰发展期随点火提前角的增大而变长,燃烧相位角随点火提前角、负荷的增大而提前,速燃期随负荷的增加、点火提前角的增大逐渐缩短;生物质气中的氢含量加快了生物质气发动机的燃烧速度.     

Analysis of the effects of reformate (hydrogen/carbon monoxide) as an assistive fuel on the performance and emissions of used canola-oil biodiesel

Evolving technology and a reoccurring energy crisis creates a continued investigation into the search for sustainable and clean-burning renewable fuels. One possibility is hydrogen that has many desirable qualities such as a low flammability limit promoting ultra-lean combustion, high laminar flame speed for increased thermal efficiency and low emissions. However, past research discovered certain limiting factors in its use such as pre-ignition in spark ignition engines and inability to work as a singular fuel in compression ignition engines. To offset these issues, this work documents manifold injection of a hydrogen/carbon monoxide mixture in a dual-fuel methodology with biodiesel. While carbon monoxide does degrade some of the desirable properties of hydrogen, it acts partially like a diluent to restrict pre-ignition. The result of this mixture addition allows the engine to maintain power while reducing biodiesel fuel consumption with a minimal NO_x emissions increase.     

The utilization of hydrogen in hydrogen/diesel dual fuel engine

A hydrogen fueled internal combustion engine has great advantages on exhaust emissions including carbon dioxide (CO₂) emission in comparison with a conventional engine fueling fossil fuel. In addition, if it is compared with a hydrogen fuel cell, the hydrogen engine has some advantages on price, power density, and required purity of hydrogen. Therefore, they expect that hydrogen will be utilized for several applications, especially for a combined heat and power (CHP) system which currently uses diesel or natural gas as a fuel.A final goal of this study is to develop combustion technologies of hydrogen in an internal combustion engine with high efficiency and clean emission. This study especially focuses on a diesel dual fuel (DDF) combustion technology. The DDF combustion technology uses two different fuels. One of them is diesel fuel, and the other one is hydrogen in this study. Because the DDF engine is not customized for hydrogen which has significant flammability, it is concerned that serious problems occur in the hydrogen DDF engine such as abnormal combustion, worse emission and thermal efficiency.In this study, a single cylinder diesel engine is used with gas injectors at an intake port to evaluate performance swung the hydrogen DDF engine with changing conditions of amount of hydrogen injected, engine speed, and engine loads. The engine experiments show that the hydrogen DDF operation could achieve higher thermal efficiency than a conventional diesel operation at relatively high engine load conditions. However, it is also shown that pre-ignition with relatively high input energy fraction of hydrogen occurred before diesel fuel injection and its ignition. Therefore, such abnormal combustion limited amount of hydrogen injected. Fire-deck temperature was measured to investigate causal relationship between fire-deck temperature and occurrence of pre-ignition with changing operative conditions of the hydrogen DDF engine.     

天然气发动机在不同喷射和点火时刻下的性能优化研究

为解决改装的天然气发动机动力性比原柴油机低,燃料消耗率比原柴油机高的问题,对影响燃烧时刻的喷射提前角与点火提前角这两个重要参数进行模拟实验,研究其对发动机的缸内压力与功率、燃气消耗率的影响,并根据研究结果进行优化设计。结果表明,对于缸内直喷天然气发动机,适当增大喷气提前角和选择恰当的点火提前角能在较经济的情况下提高发动机的动力性;发动机转速增加,点火提前角和喷射提前角也应提前,保证燃料的充分混合和最大化做功能力;在所有转速下,天然气发动机的功率都能恢复到原柴油机的水平。     

Research on diagnosis of pre-ignition of hydrogen engine based on SOM-MAS

Abnormal combustion is an important factor in the development process of hydrogen engine and it mainly includes pre-ignition, backfire and knocking, among which pre-ignition has the most serious impact on hydrogen engine. In this paper, it is divided into four types: normal combustion, slight pre-ignition, moderate pre-ignition and severe pre-ignition according to different crankshaft rotation angles. In order to identify different combustion types, this paper proposes a fault diagnosis model based on the fusion of SOM neural network and Multi-Agent System (SOM-MAS). Firstly, different combustion types are identified by SOM. Secondly, the abnormal combustion is tracked and located mainly through the Multi-Agent System, and the location of the abnormality is identified. Finally, based on 44 sets of pressure data samples collected from the in-cylinder combustion of a hydrogen engine on the experimental bench, different combustion types were diagnosed and identified, and the location of abnormal combustion faults was tracked, which verifies the effectiveness of the proposed method shows that the method has certain feasibility and superiority for the diagnosis of hydrogen engine pre-ignition.     

A hydrogen injection system with solenoid valves for a four-cylinder hydrogen-fuelled engine

A four-cylinder four-stroke water-cooled gasoline engine with spark ignition is refitted to an in-cylinder injection spark-ignition hydrogen-fuelled engine, and the concept of its test apparatus is set up. The study to be reported in this paper focuses mainly on modification for its hydrogen supply system and combustion system to solve such problems as small power output and abnormal combustion in a hydrogen-fuelled engine. A fast response solenoid valve, which possesses good switch characteristics and very fast response, and its electronic control system are described. A high pressure hydrogen injector is designed to improve hydrogen jet penetration and mixture formation in the combustion chamber, and to prevent backfire occurring in the hydrogen supply pipe between the fast response valve and the combustion chamber. Ignition by spark plug is adopted and an Intel 8098 chip microprocessor is developed to control ignition and injection timing optimally. This study shows that abnormal combustion, such as backfire, pre-ignition, high pressure rise rate and knock, can be controlled and performance of the engine can be improved by means of this system.     

Research on optimum method to eliminate backfire of hydrogen internal combustion engines based on combining postponing ignition timing with water injection of intake manifold

Preignition or backfire occurs easily in hydrogen internal combustion engines (HICE) of manifold injection type, especially, the bigger equivalence ratio is, the more serious backfire happens. And decreasing equivalence ratio will reduce engine's power output. So to analyze and resolve the contradiction between abnormal combustion and power output in HICE is the key of promoting the progress of research on HICE. Postponing ignition timing is helpful to reducing the occurrence degree or inclination of pre-ignition, and water injection of intake manifold can be used to eliminate backfire. But postponement of ignition has a lesser effect on power output and brake thermal efficiency than water injection of intake manifold, That is to say water injection would bring power output to drop obviously, and water injection will also has many disadvantages, such as, the worse corrosion degree of cylinder and deteriorated lubrication performance. It is necessary to combine postponing ignition timing with water injection of intake manifold to give full play to their advantages, and avoid their disadvantages to the greatest extent. In the paper, the concept of pre-ignition strength and backfire strength were presented, and the inhibition degree of pre-ignition and the elimination degree of backfire was introduced. The functional relationship between inhibition degree of pre-ignition and ignition timing was established, and the functional relationship between the elimination degree of backfire and water injection rate was also established for quantitative analysis and research into inhibiting pre-ignition and eliminating backfire. A optimal control method was put forward about resolving contradiction between eliminating backfire and improving performance of HICE, which not only eliminates backfire, but also take into account the power output and economy.     

Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine

An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO₂ concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO₂ do not vary much with hydrogen addition. The exhaust NO_x increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%.     

Recent studies on hydrogen usage in Wankel SI engine

In this study, investigations on the hydrogen usage in spark ignition (SI) rotary engines are reviewed to assess trend researches. Many scientists conducted various studies to investigate performance, emission and combustion characteristics of hydrogen technology. The studies generally focused on their usage as an additive fuel. It can be seen that hydrogen usage in SI engine are very promising for their lower emissions, more efficient combustion, and higher power output. Nevertheless, hydrogen utilization may cause combustion problems such as back fire, auto and pre-ignition. Moreover, because of their small molecular structure hydrogen storage is another issue. Especially, hydrogen blending is a particular solution and this makes hydrogen gas tolerable for storage and transporting problem. In the recent studies, hydrogen usage in rotary engine is found well suited and feasible by scientists. Combustion difficulties caused by long and narrow shaped combustion chamber and long quenching distance of this type of engine can be solved by hydrogen addition. However, absence of a light, safe and low cost storage technology are still bottlenecks for their usage and waiting for solution.     

液化石油气与汽油燃烧特性的对比试验研究

在点燃式发动机上分别燃用液化石油气和汽油,通过采集示功图并进行放热规律计算,对两种燃料在相似工况、相同过量空气系数下的燃烧特性进行对比分析。结果表明,在不改变样机结构和点火提前角的情况下,燃用液化石油气造成样机最大输出功率下降了7.64%。标定工况下,过量空气系数的变化对样机燃用汽油时的功率影响较大。两种燃料标定工况下的比热耗均随过量空气系数的增大而降低,但液化石油气降低的幅度较小。相似工况、相同过量空气系数下,相对于汽油,液化石油气的滞燃期短,燃烧持续期短,燃烧速度快。     

Efficiency and pollutant emissions of an SI engine using biogas-hydrogen fuel blends: BIO60, BIO95, H20BIO60 and H20BIO95

Our planet has been experiencing abrupt climate changes in recent years. The major contributor to this phenomenon is, without doubt, emissions of gases derived from petroleum-based fuels, compared to their high consumption, especially diesel and gasoline. In Brazil, the sum of all motorized trips shows that more than half of them (60%) is based on public transport, with buses carrying 94% of all those who use this service. These vehicles, in their vast majority, use the technology of Compression Ignition (CI) engines. On the other hand, studies have shown that the country has a high biofuel production potential from various sources, such as landfills and hydroelectric plants, with an extensive production of biogas and hydrogen, that can be used, for example, in Spark Ignition (SI) engines. Nevertheless, SI engines have lower efficiency than CI engines. Part load operation of SI engines is conventionally achieved by the use of a throttle to control the airflow or air-fuel mixture into the engine. When operating at partial load the throttle causes exergy losses what affecting on decreasing engine efficiency. With the objective of analysing the emission of pollutants and the efficiency of conversion of fuel chemical energy, this work presents an analysis on the use of blends of hydrogen (H₂), biogas (BIO60) and methane (BIO95) using an SI engine. The system was operated in partial load and the addition of H₂ was an attempt to increase efficiency by reducing the pumping work through the throttle, once it was possible increasing the lambda value. The tests were performed at different ignition angles and air/fuel ratio. The value of ignition advance angle has been adjusted to obtain maximum Brake Thermal Efficiency (BTE) of the engine. It was possible to recognize that the addition of H₂ allowed the combustion limits to be extended. On the other hand, reduced values of CO and NO_x emissions could be achieved.     

Explorations of the impacts on a hydrogen fuelled opposed rotary piston engine performance by ignition timing under part load conditions

High power density of opposed rotary piston (ORP) engines provides a possibility for the applications to hybrid vehicles. Under real driving conditions, internal combustion engines as the power sources of hybrid vehicles run under part load conditions in majorities of operation time. Hydrogen applications in internal combustion engines will promote zero-carbon travel, contributing to alleviating global warming. In this investigation, 3D numerical simulations were conducted to explore the performance of an ORP engine fuelled with hydrogen under part load and various ignition timing conditions. The results indicated that peak in-cylinder pressure and corresponding crank angle (CA) changed slightly within the early ignition range of ?20.85º CA~ ?14.23º CA; peak in-cylinder pressure was decreased significantly by late ignition. Heat release rates were more sensitive to late ignition than early ignition. Start of combustion, combustion phase, and combustion durations presented minor impacts by early ignition and engine loads. Ignition timing of ?20.85º CA~ ?11.06º CA showed limited impacts on indicated mean effective pressure and indicated power over individual intake manifold pressure. Indicated thermal efficiency was around 40% for the ignition timing of ?20.85º CA~ ?11.06º CA over the intake manifold pressure of 0.8 bar; indicated thermal efficiency drop caused by ignition timing of ?8.33º CA was higher than 7% compared with optimal conditions. Heat loss by cylinder walls in proportions of fuel energy was lower than 25%, 20%, 18% for the intake manifold pressure of 0.4 bar, 0.6 bar, 0.8 bar respectively. Energy loss by the exhaust was higher than 41% for all the scenarios, with the maximum value being approximately 57%. Nitrogen oxides (NO_x) emission factors were higher than 11 g (kW h)^?1, and they were increased significantly by early ignition.     

直喷式柴油机瞬态工况燃烧噪声二级影响机理研究

研究直喷式柴油机瞬态工况燃烧噪声二级影响机理。设计瞬态与稳态工况燃烧噪声试验，测量燃烧噪声二级影响因素，分析瞬态工况下壁面温度、油管压力和针阀升程等间接因素影响动力负荷与压力高频振荡，从而影响燃烧噪声的二级影响机理，并对不同供油提前角瞬态工况燃烧噪声二级影响机理进行了研究。结果表明，瞬态工况壁面温度、油管压力、针阀升程及针阀开启时间均高于同负荷同转速的稳态工况，影响到瞬态工况滞燃期以及滞燃期的喷油量，进而影响动力负荷和压力高频振荡，使得瞬态与稳态工况燃烧噪声产生差异。     

Multi-dimensional modeling of mixture preparation in a direct injection engine fueled with gaseous hydrogen

With the recent advances of direct injection (DI) technology, introducing hydrogen into the combustion chamber through DI is being considered as a viable approach to circumvent backfire and pre-ignition encountered in early generations of hydrogen engines. As part of a broader vision to develop a robust numerical model to study hydrogen spark ignition (SI) combustion in internal combustion (IC) engines, the present numerical investigation focuses on mixture preparation in a hydrogen DI SI engine. This study is carried out with a single hole injector with gaseous hydrogen injected at 100 bar injection pressure. Simulations are carried out for high and low tumble configurations and validated against optical data acquired from planar laser induced fluorescence (PLIF) measurements. Varying mesh configurations are investigated for the impact on in-cylinder mixture distribution. A particular emphasis is placed on the effect of nozzle geometry and mesh orientation near the wall. Overall, the computational model is found to predict the mixture distribution in the combustion cylinder reasonably well. The results showed that the alignment of mesh with the flow direction is important to achieve good agreement between numerical analysis and optical measurement data.     

Effect of compression ratio, equivalence ratio and engine speed on the performance and emission characteristics of a spark ignition engine using hydrogen as a fuel

The present energy situation has stimulated active research interest in non-petroleum and non-polluting fuels, particularly for transportation, power generation, and agricultural sectors. Researchers have found that hydrogen presents the best and an unprecedented solution to the energy crises and pollution problems, due to its superior combustion qualities and availability. This paper discusses analytically and provides data on the effect of compression ratio, equivalence ratio and engine speed on the engine performance, emissions and pre-ignition limits of a spark ignition engine operating on hydrogen fuel.These data are important in order to understand the interaction between engine performance and emission parameters, which will help engine designers when designing for hydrogen.     

柴油-小桐子掺混油柴油机工作过程及循环变动分析

以柴油和柴油-小桐子掺混油在单缸水冷四冲程柴油机上进行试验,测录了多循环的瞬时气缸压力与高压油管燃油压力,对比分析了不同转速的全负荷工况与标定点转速不同负荷工况,燃用柴油与掺混油的喷油与燃烧过程及燃烧过程中各参数的循环变动.结果发现,喷油率随转速升高而升高;喷油始点随转速升高略微推迟,随负荷增大而提前;掺混油燃烧始点早于柴油,燃烧始点随转速升高延后,随负荷增大而提前,燃烧始点的循环变动量随转速升高而增大;高转速、高负荷时的最高燃烧压力循环变动率较小;掺混油的最大燃烧压力升高率低于柴油,最大压力升高率循环变动率随转速升高、负荷减小而增大.     

Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine

An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO₂ concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO₂ do not vary much with hydrogen addition. The exhaust NOx increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%. __________ Translated from Transactions of CSICE, 2006, 24(5): 394–401 [译自:内燃机学报]