火花点火发动机实现稀薄燃烧的技术措施

本文介绍了火花点火发动机稀薄燃烧的特点及实现稀薄燃烧所采用的关键技术措施，文章指出：实现稀薄燃烧是提高车用火花点火发动机的经济性和改善排放性能的重要途径。     

天然气发动机多点顺序喷射技术的开发研究

介绍天然气发动机多点顺序喷射系统的开发研究，试验在原F913C柴油机上进行，对原机的进气系统和燃烧系统进行了改进，采用高能点火。电控系统精确控制点火时刻、燃气喷射量，通过三元催化剂控制排放。发动机通过了动力性和排放的测试，达到了动力性要求并满足欧Ⅱ排放标准。     

采用高能点火的均质稀薄燃烧汽油机试验

均质稀薄燃烧能够有效提高汽油机热效率,而高能点火可以提高汽油机的燃烧速度,是实现均质稀薄燃烧的有效技术途径.通过一台单缸汽油机分别研究了普通火花点火和高能点火对均质稀薄燃烧过程的影响,分析了两者燃油经济性、燃烧特性以及NOx排放特性的差异,结果表明:相比于普通火花点火,高能点火能够有效拓宽汽油机均质稀薄燃烧的空燃比极限;采用高能点火系统A可以实现过量空气系数φa为1.65的均质稀薄燃烧,指示燃油消耗率(ISFC)最低达到184.0 g/(kW·h);采用点火能量更高的高能点火系统B可以实现φa为1.94的均质超稀薄燃烧,指示燃油消耗率最低达到180.7 g/(kW·h),对应的指示热效率为48.2%;将φa进一步提升至2.00时,NO_x原始排放将降至188×10~(-6),但受限于燃烧过程恶化,此时ISFC将增加至185.3 g/(kW·h).     

火花点火式二冲程天然气发动机的开发

天然气具有高辛烷值及大Ｈ、Ｃ比且容易实现稀薄燃烧的优点。象内燃机的燃料一样纯天然气具有极好的性能。为更好地利用天然气的性能，我们把压缩天然气应用到火花点火式二冲程发动机上并对这种发动机的性能、热效率及排放进行了研究。结果，研制出更低排气污染，更少ＣＯ２排放和高热效率的压缩天然气发动机。本文报告其研究结果。     

电控喷射稀燃天然气发动机的开发

进行了发动机进气系统、燃烧系统、天然气供给系统、点火系统和电控系统等的设计。研究了天然气发动机稀薄燃烧规律,提出了空燃比分区控制的稀薄燃烧控制方案,实现了不采用EGR情况下NO,排放物的有效控制,仅通过匹配氧化催化转化器,使发动机排放达到了欧Ⅲ（ESC）法规要求。试验结果表明,CA6SE1—21N天然气发动机不仅达到了原柴油机的标定功率水平,而且具有良好的可靠性。     

火花点火式二冲程天然气发动机的开发

天然气具有高辛烷值及大Ｈ、Ｃ比且容易实现稀薄燃烧的优点。象内燃机的燃料一样纯天然人有极好的性能。为更好地利用天然气的性能，我们把压缩天然气应用到火花点火式二冲程发动机上并对这种发动机的性能、热效率及排放进行了研究。结果，研制出更低排气污染，更少ＣＯ２排放和高热效率的压缩天然气发动机。本文报告其研究结果。     

满足国-IV排放的电控稀燃天然气发动机燃烧系统开发

针对电控单点喷射稀燃天然气发动机燃烧系统进行了开发研究.在原柴油机上加装了电控系统、天然气供气系统和点火系统,并对燃烧室结构和凸轮轴参数进行了优化设计,以适应稀燃天然气发动机的要求.研究了燃烧室形状、压缩比和凸轮轴型线、配气相位对天然气发动机性能和排放的影响,确定了最终的匹配方案.结果表明:采用优化设计的无气门重叠角凸轮轴和压缩比为11的直口碗形燃烧室,所开发的天然气发动机具有良好的动力性、经济性,安装氧化型后处理器的排放结果达到国-IV排放法规要求.     

天然气发动机点火系统研发的理论与实践(上)

点火系统对发动机性能有非常重要的影响,点火系统的研发是一个跨电磁学和内燃机燃烧学科的课题。本文回顾了汽车点火系统的发展历程,对一汽锡柴的天然气发动机点火系统技术水平进行定位;研究了点火系统各变量之间的关系及其对发动机燃烧和性能的影响;研究了天然气发动机与汽油发动机点火系统所需击穿介质的物理和化学特性的差异;参考点火能量模拟计算和测试结果,确定一汽锡柴6SN1天然气发动机点火系统点火能量;综合平衡点火系统性能、寿命、成本,确定一汽锡柴6SN1天然气发动机点火系统的主要零件结构参数、性能参数;为满足更高排放要求,针对不同排放控制策略、提出未来点火系统的发展方向。     

湍流射流点火对天然气发动机燃烧特性影响的试验研究

湍流射流点火（Turbulent Jet Ignition,TJI）是一种有效的燃烧增强技术,可提供更高的点火能量,使发动机稳定着火,且可以提高燃烧压力和燃烧速率,缩短燃烧持续期,是实现发动机稀薄燃烧的有效手段。基于一台带有预燃室的点燃式单缸试验机,开展了TJI模式下天然气发动机性能的试验研究。首先,研究了不同过量空气系数下TJI对天然气发动机动力性能、排放性能及燃烧特性的影响,并与火花塞点火（Spark Ignition,SI）模式进行对比;其次,在稀燃条件下分别探究了进气增压和预燃室喷氢对天然气发动机动力性、经济性及燃烧过程的优化作用。结果表明：TJI的使用可有效拓展天然气发动机的稀燃极限,且燃烧滞燃期和燃烧持续期均更短,放热率更高;过量空气系数1.5为甲烷TJI最佳稀燃工况,此时燃油消耗率最低,且可实现氮氧化物近零排放;此外,采用进气增压的方式可以提高TJI发动机在高负荷下的经济性;TJI模式下,相较于预燃室喷甲烷,预燃室喷氢气可进一步缩短滞燃期和燃烧持续期,提高放热率,达到提升TJI性能的效果。     

混燃模式在燃气发动机国Ⅴ排放中的应用

重型天燃气发动机采用缸外预混合燃烧方式,空燃比决定着天然气发动机排放及动力性能。采用当量燃烧/稀薄燃烧相结合的混合燃烧方式,在中低负荷区,通过当量燃烧和三效催化器降低排气中各种污染物的浓度、减小循环波动、提高整车驱动性;在大负荷区,通过稀薄燃烧降低NOx原始排放,同时降低热负荷、提高经济性,发动机本体不需作重大改进即可满足国Ⅴ排放及驱动性的要求。     

汽油/CNG混合燃料发动机的性能和燃烧特性研究

研究了汽油／CNG混合燃料的发动机性能和燃烧特性。在研制汽油／CNG发动机集中电子控制单元基础上,研究了不同汽油和天然气混合比例对发动机动力性能、排放性能的影响,结果表明,随着混合燃料中天然气比例的增加,发动机的功率和转矩下降,HC和NOx排放降低,在不同负荷下应供给发动机不同比例的汽油和天然气,这样既可以获得较好的发动机动力性能,又可以实现发动机低排污特性;对燃烧特性的研究结果表明,在天然气中混入汽油有利于改善天然气的燃烧特性,混合物的燃烧特性参数随两种燃料的混合比的不同而不同,其值界于天然气和汽油之间。     

Effect of natural gas enrichment with hydrogen on combustion process and emission characteristic of a dual fuel diesel engine

The paper presents results of experimental research on a dual-fuel engine powered by diesel fuel and natural gas enriched with hydrogen. The authors attempted to replace CNG with hydrogen fuel as much as possible with a constant dose of diesel fuel of 10% of energy fraction. The tests were carried out for constant engine load of IMEP = 0.7 MPa and a rotational speed of n = 1500 rpm. The effect of hydrogen on combustion, heat release, combustion stability and exhaust emissions was analyzed. In the test engine, the limit of hydrogen energy fraction was 19%. The increase in the fraction caused an increase in the cycle-by-cycle variation and the occurrence of engine knocking. It was shown that the enrichment of CNG with hydrogen allows for the improvement in the combustion process compared to the co-combustion of diesel fuel with non-enriched CNG, where the reduction in the duration of combustion by 30% and shortening the time of achieving 50% of MFB by 50% were obtained. The evaluation of the spread of the end of combustion is also presented. For H₂ energetic share over 20%, the spread of end of combustion was 48° of crank angle. Measurement of exhaust emissions during the tests revealed an increase in THC and NO_x emissions.     

Investigation on soot emissions from diesel-CNG dual-fuel

The burning of diesel and compressed natural gas (CNG) is attractive compared to diesel fuel because of the reduction of CO₂ emissions and particulate matter (PM) emissions. While soot emissions from the diesel-CNG combustion can be tested in a real-world single-cylinder engine, the soot formation characteristics cannot be tested in the same way. Therefore, to understand the mechanisms behind soot formation in diesel-CNG combustion, soot evolution must be investigated using a simulation model. In this study, the soot evolution is investigated under different CNG substitution ratios with single and split fuel injection. An AVL 5402 single-cylinder diesel engine was modified to run diesel/CNG dual-fuel to investigate the combustion and soot emissions. A new soot model using KIVA-3V R2 code and integrated with a reduced heptane/methane PAH (polycyclic aromatic hydrocarbons) mechanism was used to simulate soot behavior. For the combustion, the results show that the ignition delay gets extended, the combustion duration gets shorter and the peak pressure can be improved when CNG substitution ratio is increased both with single and split injection. Additionally, a slight increase of pressure is observed when the split injection is used. This is because the split injection is an effective strategy to change the distribution and vaporization of fuel, which results in an incremental increase in combustion efficiency and increase pressure. As the CNG substitution ratio is increased, soot emissions get drastically reduced. The reason is the equivalence ratio distribution of air-fuel becomes more homogenous and the local fuel-rich region shrinks with increasing of CNG substitution ratios. Pyrene is an important intermediate specie to generate soot particles. The results show that pyrene distribution decreases, leading to a reduced generation of soot precursors. As a result, the soot mass of CNG70 is less than the other two cases. The basic reason is the prolonged ignition delay allowed for more time for fuel−air mixing, which reduces soot mass formation.     

Emissions and fuel consumption characteristics of an HCNG-fueled heavy-duty engine at idle

The idle performance of an 11-L, 6-cylinder engine equipped with a turbocharger and an intercooler was investigated for both compressed natural gas (CNG) and hydrogen-blended CNG (HCNG) fuels. HCNG, composed of 70% CNG and 30% hydrogen in volume, was used not only because it ensured a sufficient travel distance for each fueling, but also because it was the optimal blending rate to satisfy EURO-6 emission regulation according to the authors' previous studies. The engine test results demonstrate that the use of HCNG enhanced idle combustion stability and extended the lean operational limit from excess air ratio (λ) = 1.5 (CNG) to 1.6. A decrease of more than 25% in the fuel consumption rate was achieved in HCNG idle operations compared to CNG. Total hydrocarbon and carbon monoxide emissions decreased when fueled with HCNG at idle because of the low carbon content and enhanced combustion characteristics. In particular, despite hydrogen enrichment, less nitrogen oxides (NO_x) were emitted with HCNG operations because the amount of fuel supplied for a stable idle was lower than with CNG operations, which eventually induced lower peak in-cylinder combustion temperature. This low HCNG fuel quantity in idle condition also induced a continuous decrease in NO_x emissions with an increase in λ. The idle engine test results also indicate that cold-start performance can deteriorate owing to low exhaust gas temperature, when fueled with HCNG. Therefore, potential solutions were discussed, including combustion strategies such as retardation of spark ignition timing combined with leaner air/fuel ratios.     

天然气发动机空燃比的自适应控制研究

提出一种新的天然气发动机空燃比自适应控制策略。通过对空燃比实施抖动形成寻优控制因素的变化，测量发动机转速波动差作为寻优控制响应的判据，实现以燃料经济性为寻优目标的闭环优化控制，并用于现有氧传感器无法使用的稀燃天然气发动机。通过软件和硬件控制系统设计，尤其是抗干扰设计，在一台单缸天然气发动机上进行应用，验证了其可行性。     

气口顺序喷射、稀燃、全电控柴油／天然气双燃料发动机的研究

采用气口顺序喷射、稀燃、全电控柴油／天燃气双燃料发动机方案,对斯太尔WD615．64增压非中冷柴油机进行了改装。试验结构表明,改装后的发动机NOx、颗粒和NMHC排放均达到了欧Ⅱ排放指标。CO和HC（含甲烷）可以通过后处理解决。     

Syngas (H2/CO) in a spark-ignition direct-injection engine. Part 1: Combustion,performance and emissions comparison with CNG

The combustion, performance, and emissions of syngas (H₂/CO) in a four-stroke, direct-injection, spark-ignition engine were experimentally investigated. The engine was operated at various speeds, ranging from 1500 to 2400 rev/min, with the throttle being held in the wide-open position. The start of fuel injection was fixed at 180° before the top dead center, and the ignition advance was set at the maximal brake torque. The air/fuel ratio was varied from the technically possible lowest excess air ratio (λ) to lean operation limits. The results indicated that a wider air/fuel operating ratio is possible with syngas with a very low coefficient of variation. The syngas produced a higher in-cylinder peak pressure and heat-release rate peak and faster combustion than for CNG. However, CNG produced a higher brake thermal efficiency (BTE) and lower brake specific fuel consumption (BSFC). The BTE and BSFC of the syngas were on par to those of CNG at higher speeds. For the syngas, the total hydrocarbon emission was negligible at all load conditions, and the carbon monoxide emission was negligible at higher loads and increased under lower load conditions. However, the emission of nitrogen oxides was higher at higher loads with syngas.     

天然气成分对发动机性能及排放影响的试验研究

在同一台发动机上通过燃用属于同类别的两地天然气的对比试验,研究了天然气（CNG）成分对发动机性能及排放的影响。试验结果表明：天然气成分的差异导致发动机的空燃比发生变化,是造成发动机性能与排放产生较大变化的主要原因,而控制发动机空燃比在较小范围变化,可以减少天然气成分对发动机性能及排放的影响。     

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%.