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%.     

不同点火时刻下天然气掺氢缸内直喷发动机燃烧与排放特性

在缸内直喷火花点火发动机上开展了天然气掺混0％-18％氢气的混合燃料不同点火时刻下的试验研究。结果表明：对于给定的喷射时刻和喷射持续期，点火时刻对发动机性能、燃烧和排放有较大影响，喷射结束时刻与点火时刻的间隔对直喷天然气发动机极为重要，喷射结束时刻与点火时刻的间隔缩短时，混合气分层程度高，燃烧速率快，热效率高。最大放热率等燃烧特征参数随点火时刻的提前而增加。HC排放随点火时刻的提前而下降，CO2和NOx排放随点火时刻的提前而增加，NOx排放的增加在大点火提前角下更明显。掺氢可降低HC排放，对CO和CO2排放影响不大。掺氢量大于10％时可提高天然气发动机热效率。     

Combustion and emission characteristics of an Acetone-Butanol-Ethanol (ABE) spark ignition engine with hydrogen direct injection

Butanol could reduce emissions and alleviate the energy crisis as a bio-fuel used on engines, but the production cost problem limits the application of butanol. During the butanol production, ABE (Acetone-Butanol-Ethanol) is a critical intermediate product. Many studies researched the direct application of ABE on engines instead of butanol to solve the production cost problem of butanol. ABE has the defects of large ignition energy and vaporization heat. Hydrogen is a gaseous fuel with small ignition energy and high flame temperature. In this research, ABE port injection combines with hydrogen direct injection, forming a stratified state of the hydrogen-rich mixture around the spark plug. The engine speed is 1500 rpm, and λ is 1. Five αH₂ (hydrogen blending fractions: 0, 5%, 10%, 15%, 20%) and five spark timings (5°, 10°, 15°, 20°, 25° CA BTDC) are studied to observe the effects of them on combustion and emissions of the test engine. The results show that hydrogen addition increases the maximum cylinder pressure and maximum heat release rate, increases the maximum cylinder temperature and IMEP, but the exhaust temperature decreases. The flame development period and flame propagation period shorten after adding hydrogen. Hydrogen addition improves HC and CO emissions but increases NO_x emissions. Particle emissions decrease distinctly after hydrogen addition. Hydrogen changes the combustion properties of ABE and improves the test engine's power and emissions. The combustion in the cylinder becomes better with the increase of αH₂, but a further increase in αH₂ beyond 5% brings minor improvements on combustion.     

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]     

Research on combustion and emission characteristics of a hydrous ethanol/hydrogen combined injection spark ignition engine under lean-burn conditions

Ethanol, as one of the carbon-neutral fuels for spark ignition (SI) engine, has been widely used. Dehydration and purification of ethanol during production process will lead to high energy consumption. If hydrous ethanol can be directly applied to the engine, the cost of use will be greatly reduced. Due to the high latent heat of vaporization of ethanol and water, it is necessary to consider the performance of atomization, evaporation and combustion stability when hydrous ethanol is used in engine. As a zero-carbon fuel, hydrogen has excellent characteristics such as low ignition energy, fast flame propagation speed and wide combustion limit. The combination of hydrous ethanol and hydrogen can reduce the use cost and ensure better combustion performance. Therefore, this study explores the performance of hydrous ethanol/hydrogen in SI combined injection engine. The hydrous ethanol is injected into the intake port and the hydrogen is directly injected into the cylinder during the compression stroke. In this study, we firstly analyze the optimal water blending ratio (ω) of hydrous ethanol, which including 0, 3%, 6%, 9% and 12%. The experimental results show that the hydrous ethanol with 9% water ratio has the best performance without hydrogen addition. Based on the 9% water ratio, the effects of hydrogen blending ratio (0, 5%, 10%, 15% and 20%) on the combustion and emission under different excess air ratio (λ) (1, 1.1, 1.2, 1.3, 1.4). Hydrogen addition can increase the degree of constant volume combustion, so that the maximum cylinder pressure and temperature increase with the increase of the hydrogen blending ratio (HBR). When λ = 1.3 and HBR = 20%, the maximum in-cylinder pressure can be increased by 108.64% compared to pure hydrous ethanol. Hydrogen effectively increases the indicated mean effective pressure (IMEP) and reduces the coefficient of variation of IMEP (COV_IMEP). Adding hydrogen can reduce CO and HC emissions, while NO_x emissions will increase. When λ = 1.2 and HBR increasing from 0 to 20%, the NOx emissions increase by 106.75%, but it is still less than the NOx emissions of pure hydrous ethanol at λ = 1. On the whole, hydrogen direct injection can improve the combustion performance of hydrous ethanol and achieve stable combustion under lean-burn conditions.     

运行工况对基础燃料均质压燃燃烧过程影响的试验研究

在一台经改装的单缸直喷式柴油机上进行了不同辛烷值基础燃料下发动机转速对均质压燃（HCCI）燃烧特性、工况范围和排放特性影响的试验研究。研究结果表明：发动机转速升高，不同辛烷值燃料着火燃烧时刻推迟，以曲轴转角计算的燃烧持续期延长，高辛烷值燃料的缸内最大爆发压力和缸内温度降低；在中间转速，HCCI实现的最高平均指示压力最大，高转速工况，最高平均指示压力降低；对于低辛烷值燃料，转速对燃烧效率影响不大，转速升高，指示热效率增大；对于高辛烷值燃料，转速升高燃烧效率降低，指示热效率在中间转速最高，高转速降低。排放测试表明，转速升高使得HCCI运转的HC和CO排放都升高，NOx排放则逐渐降低。     

Inhibition effect of doping methyl tert-butyl ether compounds to n-heptane on homogenous charge compression ignition combustion

This article reports an experimental study on the combustion characteristics and emissions of homogenous charge compression ignition (HCCI) combustion using n-heptane doped with methyl tert-butyl ether (MTBE). The experiments were conducted on a single cylinder HCCI engine using neat n-heptane and 10%, 20%, 30%, 40% and 50% (by volume) MTBE/n-heptane blends at constant engine speed. The experimental results reveal that the ignition timing of the low temperature reaction (LTR) gets retarded, the peak values of heat release during the LTR decrease and the negative temperature coefficient (NTC) duration gets prolonged with the increase of MTBE in the blends. Consequently, the ignition timing of the high temperature reaction (HTR) gets delayed and both the attainable maximum indicated mean effective pressure (IMEP) and the lowest stable IMEP increase. Parametric studies on CO and HC emissions reveal that the maximum combustion temperature, pressure rise rate, IMEP, ignition timing of the HTR, combustion duration and fuel components have important impacts on HC emission, while the main parameters that show an important influence on CO emissions are the maximum combustion temperature, pressure rise rate, IMEP and combustion duration. Moreover, in order to suppress the CO and HC emissions to a low level, the maximum combustion temperature should be higher than 1500 K, the maximum pressure rise rate larger than 0.5 MPa/°CA, the IMEP above 0.3 MPa and the combustion duration shorter than 9 °CA.     

Investigation of hydrogen addition to methanol-gasoline blends in an SI engine

In this study, effects of hydrogen-addition on the performance and emission characteristics of Methanol-Gasoline blends in a spark ignition (SI) engine were investigated. Experiments were conducted with a four-cylinder and four stroke spark ignition engine. Performance tests were performed via measuring brake thermal efficiency, brake specific fuel consumption, cylinder pressure and exhaust emissions (CO, CO₂, HC, NOx). These performance metrics were analyzed under three engine load conditions (no load, 50% and 100%) with a constant speed of 2000 rpm. Methanol was added to the gasoline up to 15% by volume (5%, 10% and 15%). Besides, hydrogen was added to methanol-gasoline mixtures up to 15% by volume (3%, 6%, 9% and 15%). Results of this study showed that methanol addition increases BSFC by 26% and decreases thermal efficiency by 10.5% compared to the gasoline. By adding hydrogen to the methanol - gasoline mixtures, the BSFC decreased by 4% and the thermal efficiency increased by 2% compared to the gasoline. Hydrogen addition to methanol – gasoline mixtures reduces exhaust emissions by about 16%, 75% and 15% of the mean average values of HC, CO and CO2 emissions, respectively. Lastly, ?t was concluded that hydrogen addition improves combustion process; CO and HC emissions reduce as a result of the leaning effect caused by the methanol addition; and CO2 and NOx emission increases because of the improved combustion.     

An experimental investigation of hydrogen-enriched gasoline in a Wankel rotary engine

The Wankel rotary engine is a potential alternative to the reciprocating engine in hybrid applications because of its favorable energy to weight ratio. In this study, a Wankel rotary engine was modified to run on a hydrogen–gasoline blend. Hydrogen enrichment improved the performance of a lean-burn spark-ignition rotary engine operating at high speed and wide open throttle conditions with the original ignition timing, using 0%, %2, 4%, 5%, 7%, and 10% hydrogen energy fractions at the intake. The experimental results showed that adding hydrogen to gasoline in the engine improved the thermal efficiency and the power output. Hydrocarbon and carbon monoxide emissions were reduced while nitrogen oxide emissions increased with the increase of hydrogen fraction.     

Influence of hydrogen co-combustion with diesel fuel on performance,smoke and combustion phases in the compression ignition engine

The main objective of this study was to examine impact of hydrogen addition to the compression ignition engine fueled with either rapeseed methyl ester (RME) or 7% RME blended diesel fuel (RME7) on combustion phases and ignition delay as well as smoke and exhaust toxic emissions. Literature review shows in general, hydrogen in those cases is used in small amounts below lower flammability limits. Novelty of this work is in applying hydrogen at amounts up to 44% by energy as secondary fuel to the compression ignition engine. Results from experiments show that increase of hydrogen into the engine makes ignition delay shortened that also affects main combustion phase. In all tests the trends of exhaust HC and CO toxic emissions vs. hydrogen addition were negative. The trend of smokiness decreased steadily with increase of hydrogen. Amounts of hydrogen addition by energy share were limited to nearly 35% due to combustion knock occurring at nominal load.     

Comparative study on air dilution and hydrogen-enriched air dilution employed in a SI engine fueled with iso-butanol-gasoline

Hydrogen and iso-butanol are notable potential alternative fuels. Hydrogen addition under air dilution conditions was investigated in this study in an attempt to enhance the thermal efficiency of spark ignition (SI) engines fueled with iso-butanol-gasoline (B33) at partial load. Hydrogen appears to have positive effect on combustion progress that is prolonged during air dilution. Under lean hydrogen-enriched mixture conditions, the brake thermal efficiency was increased by about 4% and combustion instability was reduced; the lean burn limit migrated from 1.4 to 1.8 for B33 engine after hydrogen addition. Under lean burn conditions, the durations of initial flame development and rapid burning were shortened markedly by hydrogen; both were extended by air dilution. After hydrogen addition, the unburnt HC emissions of iso-butanol-gasoline decreased markedly and carbon monoxide (CO) emissions decreased slightly. NO_x emissions from hydrogen-enriched iso-butanol-gasoline increased as lambda grew near to 1.0, at a significant reduction with increasing excess air rate regardless of fuel type. The combination of hydrogen addition and air dilution exhibited a positive inhibition on particle matter (PM) emissions regardless particle in nucleation or the accumulation mode, and the particle surface concentration was reduced significantly. Finally, an improved combustion progress was observed after hydrogen addition during air dilution, as well as a higher brake thermal efficiency and wider lean burn limit with acceptable combustion stability.     

Effect of hythane enrichment on performance,emission and combustion characteristics of an ci engine

Although compression ignition engines have high torque output and thermal efficiency, they emit lots of NO_x and smoke emissions. Moreover, total number and percentage of compression ignition engine powered vehicles in road vehicles have been increasing recent years which is called as dieselisation in EEA term reports. Dieselisation is really hazardous for human life and environment. Therefore, some governments in Europe take action to forbid using diesel engine powered vehicles in city centers. Hydrogen and methane mixture which is named as hythane can be an alternative to restrict this negative situation. For this reason, 90% methane and 10% hydrogen gas mixture was used as additional fuel in diesel engine. According to obtained results, smoke emission was decreased 95.44% at the rate of 50% gaseous fuel at 2100 rpm engine speed. However, increase of THC, CO and NO_x emissions with hythane addition weren't prevented. Using hythane in conventional diesel engines as dual operation mode will be solution to diminish dieselisation problem in near feature.     

Enhancing idle performance of an n-butanol rotary engine by hydrogen enrichment

Rotary engine generally sustains poor fuel economy and emissions performance at idle condition. Hydrogen has excellent physicochemical properties that can serve as an enhancer to improve the performance of the original engine. In this paper, a modified rotary engine equipped with dual fuel (hydrogen and n-butanol) port injection system and electronic ignition module was developed to explore the influence of hydrogen supplement on enhancing the idle performance of n-butanol rotary engine. In this study, the engine was run at the idle and stoichiometric with the original spark timing. Hydrogen volume percentage in the total intake was gradually increased from 0% to 7.9% by adjusting the fuel flow rate of n-butanol. The experimental results indicated that the engine instability and fuel energy flow rate were both reduced by enlarging the hydrogen supplying level. Combustion periods were shortened thanks to the enrichment of hydrogen. The peak chamber temperature was heightened as hydrogen fraction increased due to the improved combustion. HC and CO emissions were severally reduced by 50.4% and 85.8% when the hydrogen volume percentage was raised from 0% to 7.9%. However, NOx emissions were mildly increased because of the raised chamber temperature by increasing hydrogen fraction.     

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.     

Assessing the cyclic-variability of spark-ignition engine running on methane-hydrogen blends with high hydrogen contents of up to 50%

The cyclic variability in a spark-ignition (SI) engine is examined fueled with methane/hydrogen blends with the use of an in-house computational fluid dynamics (CFD) code. A recent methodology is followed, which has been developed with the main aim at providing accurate predictions of the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) in a fraction of time. Instead of simulating several tens of engine cycles, the methodology is based on the numerical results obtained from just 5 cycles, which are then processed for developing suitable fitted correlations of the main parameters as a function of a normalized distance. The latter expresses the distance of the spheres of the initial flame within the computational cell at the spark-plug region with the local turbulent eddy, and provides a smooth transition from the laminar burning regime to the fully turbulent one. This sub-model is included in the ignition numerical approach and is applied here in a SI engine with 3 different hydrogen contents, 10%, 30% and 50%, and three equivalence ratios, 1, 0.8 and 0.7, showing that the COV of IMEP is well predicted compared to the available measured data. Other parameters of engine cycle variations are also examined, such as the distribution of the IMEP. The variability of NO (nitric oxide) emissions is also examined, showing that for the stoichiometric cases it follows a distribution similar to a normal (Gaussian) one, while for lower ratios it is positively skewed. Overall, the methodology seems to provide reliable results for the whole range of the operating conditions examined, while the next steps of this activity will focus on similar cases for engine with variable speed and load, with the final goal to include additional mechanisms that contribute to the engine cycle variations.     

A computational study on the combustion of hydrogen/methane blended fuels for a micro gas turbines

To understand the combustion performance of using hydrogen/methane blended fuels for a micro gas turbine that was originally designed as a natural gas fueled engine, the combustion characteristics of a can combustor has been modeled and the effects of hydrogen addition were investigated. The simulations were performed with three-dimensional compressible k-ε turbulent flow model and presumed probability density function for chemical reaction. The combustion and emission characteristics with a variable volumetric fraction of hydrogen from 0% to 90% were studied. As hydrogen is substituted for methane at a fixed fuel injection velocity, the flame temperatures become higher, but lower fuel flow rate and heat input at higher hydrogen substitution percentages cause a power shortage. To apply the blended fuels at a constant fuel flow rate, the flame temperatures are increased with increasing hydrogen percentages. This will benefit the performance of gas turbine, but the cooling and the NO_x emissions are the primary concerns. While fixing a certain heat input to the engine with blended fuels, wider but shorter flames at higher hydrogen percentages are found, but the substantial increase of CO emission indicates a decrease in combustion efficiency. Further modifications including fuel injection and cooling strategies are needed for the micro gas turbine engine with hydrogen/methane blended fuel as an alternative.     

预燃室式天然气掺氢发动机燃烧及排放模拟

为探索掺氢对预燃室式大功率中速天然气发动机燃烧和排放的影响,采用计算流体动力学耦合化学动力学方法,在一台6ACD320型天然气发动机上,对氢气体积分数为0~30%的天然气-氢气混合燃料的燃烧过程进行了数值模拟.结果表明:在天然气中掺氢促使缸内产生了更多的O、OH等活性自由基,从而加速了缸内火焰传播,发动机的指示燃气消耗率下降、指示热效率提高,CO、THC和非甲烷碳氢化合物(NHMC)排放下降,NOx排放上升.对于预燃室式发动机,掺氢增加缸内火焰传播速率的效应主要体现在燃烧过程的后半段,而前半段燃烧过程中,预燃室射流对缸内混合气的湍流激扰效应对缸内湍流燃烧速率起着主导性的作用.综合比较,采用10%的掺氢比对发动机性能和排放较为有利.     

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

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

Effect of different volume fractions of ammonia on the combustion and emission characteristics of the hydrogen-fueled engine

Hydrogen internal combustion engines (ICE) will play an important role in reducing carbon emissions, but low power density and abnormal combustion problems are the main obstacles restricting the promotion of hydrogen ICE. Ammonia is a low-reactivity renewable fuel. The purpose of this study is to study the effect of different ammonia-added volume fractions on hydrogen ICE. In this experimental study, the combustion and emission characteristics of an engine fueled by a hydrogen/ammonia mixture were evaluated at part-load operating conditions. The experiment was carried out on a modified engine, the engine speed was 1300 rpm, the absolute pressure of the manifold was 61 kPa, and the volume fraction of ammonia added was 5.2%, 7.96%, and 10.68%, respectively. The test results show that the addition of ammonia changes the combustion characteristics of hydrogen. As the volume fraction of ammonia added increases, the flame development period and flame propagation period are both prolonged, and the peak heat release rate decreases. The addition of ammonia increases the power of the engine and reduces the indicated thermal efficiency. At the ignition timing of the maximum braking torque, as the volume fraction of ammonia added increases, the indicated mean effective pressure and indicated thermal efficiency increase. Adding ammonia volume fraction has little effect on Nitrogen oxides (NOx) emissions, and NOx emissions gradually increase with the delay of ignition timing.     

Effect of addition of hydrogen and exhaust gas recirculation on characteristics of hydrogen gasoline engine

The effects of exhaust gas recirculation (EGR) on combustion and emissions under different hydrogen ratios were studied based on an engine with a gasoline intake port injection and hydrogen direct injection. The peak cylinder pressure increases by 9.8% in the presence of a small amount of hydrogen. The heat release from combustion is more concentrated, and the engine torque can increase by 11% with a small amount of hydrogen addition. Nitrogen oxide (NOx) emissions can be reduced by EGR dilution. Hydrogen addition offsets the blocking effect of EGR on combustion partially, therefore, hydrogen addition permits a higher original engine EGR rate, and yields a larger throttle opening, which improves the mechanical efficiency and decreases NOx emissions by 54.8% compared with the original engine. The effects of EGR on carbon monoxide (CO) and hydrocarbon (HC) emissions are not obvious and CO and HC emissions can be reduced sharply with hydrogen addition. CO, HC, and NOx emissions can be controlled at a lower level, engine output torque can be increased, and fuel consumption can be reduced significantly with the co-control of hydrogen addition and EGR in a hydrogen gasoline engine.