Influence of laser ignition on characteristics of an engine for hydrogen enriched CNG and iso-octane usage

The study has focused on determining the laser plug effects on engine characteristics and the laser plug usage results have compared with spark plug usage. The laser ignition technique is a type of new ignition technique and an important solution that can make combustion systems more efficient. The testing of an engine with a laser plug is the novelty of the study and the tests were carried out with reference to equivalence ratio and plug power ranges. The behaviors of the engine at full load were examined so experimentally for both ignition techniques at hydrogen enriched CNG and iso-octane mixture usage. The tests were carried out for variations of 0.4–2.0 equivalence ratio and 20–120 W plug power. A mixture that 90% iso-octane and 10% HCNG in mass was used at two ignition modes in tests for 3300 rpm maximum engine torque speed. Also, the flame formation and propagation for both ignition techniques were detected via a high-speed camera. The tests have shown the laser ignition leads to more energy consumption in the rich mixture conditions and also, less energy is required in the lean conditions. The laser ignition discharge has extended the engine's lean combustion limits via a small energy input at the tests. The high-speed camera images have shown that the laser ignition reduces the Kernel flame formation and propagation time. The laser ignition technique was produced less NO_x than the conventional spark ignition method.     

Experimental based comparative exergy analysis of a multi-cylinder spark ignition engine fuelled with different gaseous (CNG,HCNG, and hydrogen) fuels

The experimental investigation was carried out on a multi-cylinder spark ignition (SI) engine fuelled with compressed natural gas (CNG), hydrogen blended CNG (HCNG) and hydrogen with varying load at 1500 rpm in order to perform comparative exergy analysis. The exergy analysis indicates that work exergy, heat transfer exergy and exhaust exergy were the highest with hydrogen at all loads due to its high flame temperature, low quenching distance, and high flame speed. The engine's exergy efficiency was the highest with hydrogen (34.23%), and it was about 24.23% and 24.08% with CNG and HCNG respectively at high load (20.25 kW). This indicates a higher potential of hydrogen to convert chemical energy input of fuel into heat and then power output. The exergy destruction was observed minimum with hydrogen at all loads, and it was drastically reduced at high loads. The combustion irreversibility which was calculated using species present during combustion, was the main contributor to exergy destruction, and it decreased with hydrogen. The minimum combustion irreversibility was 11.75% with hydrogen, followed by HCNG and CNG with 16.46% and 18.88% respectively at high load. The high quality of heat due to high in-cylinder temperature and low entropy generation during combustion caused by less number of chemical species in hydrogen combustion are the main reasons for lower combustion irreversibility with hydrogen.     

Study on the calibration coefficients of a quasi-dimensional model for HCNG engine

A quasi-dimensional model has been developed for an SI engine fuelled with natural gas/hydrogen blends, the combustion chamber was divided into two zones by the flame front, and a turbulent entrainment combustion model was conducted. This paper investigates the effects of calibration coefficients on the model, which includes the turbulence intensity coefficient C₂, the Taylor length scale coefficient C₃, and the Ignition lag coefficient C_ig. Validation by experiments is carried out under various operating conditions including different ignition timing, excess air ratio, manifold ambient pressure (MAP) and fraction of hydrogen enrichment. The results show that C_ig always stay the same at 1.52. When the fuel is pure natural gas, C₃ plays an important role in the simulation which changes from 0.95 to 2. The main factor changes from C₃ to C₂ when the hydrogen fraction increases from 30% to 55%. When the engine is fuelled by pure hydrogen C₂ to changes from 1.65 to 2.1.     

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.     

HCNG加气站的设计及实现

氢气和天然气具有相近的燃烧特性,而HCNG作为这两种燃气的混合物,综合了氢气燃烧速率快、着火极限宽、可从可再生能源制取获得的特点,以及天然气体积热值高、储量丰富、排放较低等优点而成为清洁、环保的新型动力燃料。山西省是我国主要的焦炭生产基地之一,拥有丰富的焦炭及焦炉煤气资源,在山西运行HCNG项目,可以使焦炉煤气中的氢气得到有效利用,具有良好的经济、社会效益。HCNG加气站采用的工艺主要包括将混合前的氢气和天然气调成一个压力等级、进行两种气体的混合、对混合后的气体进行加压。项目实施过程中采用流量随动式混气机实现氢气与天然气的混合,采用带钢缠绕式储气罐作为HCNG储存设备。高压HCNG用于给汽车充装作动力燃料使用,低压HNG可直接提供给工矿企业、单位和居民作生产、生活燃料使用。     

Performance and emission assessment of a multi-cylinder S.I engine using CNG & HCNG as fuels

The present study was carried out to assess the possibility of using the HCNG in the commercially available CNG vehicles, as the available literature indicated the benefits of adding hydrogen to CNG in small percentages by volume, leading to improved combustion characteristics of CNG and yielding sizeable benefits, regarding improved engine performance and reduced engine emissions in automotive applications. In the present study, a commercially available CNG manifold carburation kit, commonly known as “sequential injection” in the market, is evaluated for its operation characteristics, on a Spark Ignited (SI), MPFI automotive engine, of a mass-produced passenger vehicle, converted for gas operation, using, gasoline, CNG, HCNG 10% and HCNG 18% as fuels. In the study, the following performance parameters, torque, power, thermal efficiency, brake specific energy consumption (BSEC), lambda, engine oil temperature, exhaust gas species were measured. After exhaustive engine testing, a comparison of engine performance emission characteristics for gasoline, CNG and HCNG 10% and HCNG 18% is presented. The engine performance using the optimized MAP tables demonstrated torque and power improvements for HCNG 10% and HCNG 18% in comparison to CNG. The torque benefits up-to 6% and power benefits up-to 4% were observed. The fuel energy consumption was measured to be reduced, and improvement in fuel conversion efficiency was also observed. Hydrogen substitution in CNG helped in reducing CO, HC, CO₂ emissions for HCNG in comparison to CNG. Increase in NO_x emission was observed for HCNG in comparison with CNG. Superior engine emission characteristics in comparison to gasoline and CNG is also demonstrated. The commercially available sequential gas manifold carburation was found to be suitable for HCNG 10% and HCNG 18%.     

A fractal-based quasi-dimensional combustion model for SI engines fuelled by hydrogen enriched compressed natural gas

A quasi-dimensional model based on the concepts of fractal geometry has been developed for an SI engine fuelled with natural gas/hydrogen blends. The fundamentals of the thermodynamic model, the fractal combustion model and related equations are introduced. This paper investigates the influence of manifold absolute pressure, equivalence ratio and hydrogen fraction on fractal dimension and improves the fractal dimension expression. Comparisons are conducted between the improved and original models by the prediction outcomes. After the determination of model constants by calibration, the model predictions of cylinder pressure histories and mass fraction burned of an HCNG engine are then compared with experimental data over a wide range of loads, equivalence ratios, engine speeds and hydrogen blending ratios. The pressure profiles show that predictions of the improved model match quite well with the experimental results except for the early combustion stage. The improved model is proved to be more suitable for predicting HCNG engine performance.     

Reducing the idle speed of an SI CNG engine fueled by HCNG with high hydrogen ratio

This paper presents an experimental study aimed at idle characteristics of a CNG engine fueled by HCNG with 55% hydrogen blend. The idle speed was reduced from original 800 r/min to 750 r/min and 700 r/min, and the characteristics of combustion & emissions at reduced idle speed were investigated. It is found that, for the HCNG engine, only reducing idle speed cannot reduce fuel consumption at conditions of fixed λ. In order to reduce fuel consumption and keep the COV at rather low levels, the excess air ratio must be increased properly while reducing the engine idle speed. Due to the large valve overlap (30°) of this inlet inject HCNG engine, CH₄ emissions are mainly caused by scavenging, which account for the vast majority of THC emissions. The emissions of CO, THC and NOx are reduced with the decrease of ignition advance angle at a fixed λ.     

稀燃天然气掺氢发动机的热效率与排放特性

为了分析在天然气中掺入不同体积比的氢气对发动机经济性和排放性的影响,在一台6缸火花点火天然气发动机上开展了体积掺氢比在不同工况下对热效率和排放特性影响的试验研究.结果显示掺氢可以拓宽发动机的稀燃极限,提高燃烧速度,使得最佳转矩点火提前角(MBT)相对推迟;在点火提前角不变的情况下掺氢对热效率没有明显优势,而且会使NOx排放升高.而在MBT时,掺氢可以一定程度上提高发动机的指示热效率,降低未燃CH4和CO的排放,改善NOx与未燃碳氢(主要为CH4)的trade-off关系.掺氢的优势还体现在可以让发动机高效的工作在更稀的情况下,从而有利于降低NOx的排放和传热损失.     

Design and sizing of stand-alone photovoltaic hydrogen system for HCNG production

Hydrogen from renewable energy sources is a clean and sustainable option as a fuel and is seen as a potential alternative to gasoline in the future. However, in the near future the use of hydrogen in internal combustion engines is possible at low fraction in mixture with compressed natural gas (HCNG fuel).