甲醇发动机一维仿真及不同压缩比下的对比分析

使用GT-POWER对某1.3 T四缸汽油机改制的甲醇发动机进行了仿真计算。首先建立原机(压缩比为9.5)的一维模型,并与试验数据进行对比验证。由于甲醇的辛烷值明显高于汽油,可以提高发动机的压缩比,以提高发动机的动力性和经济性。在原机模型的基础上,以0.5的幅度从9.5逐渐增加压缩比至12,结果表明,发动机并没有出现明显的爆震现象。压缩比提高到11后,发动机的动力性有一定幅度的提升,经济性明显改善;而压缩比提高到12之后,扭矩略有提升,有效甲醇消耗率比压缩比为11时降低的幅度小,但是随之带来的是大负荷时发动机的NOx排放、燃烧噪声、机械负荷和热负荷的增加。     

活塞式航空煤油发动机性能优化及爆震抑制研究

本文基于一台压缩比可变的单缸热力学发动机,使用自主开发的空气辅助喷射系统,在全负荷条件下,开展了活塞式航空煤油发动机性能优化及爆震抑制的试验研究。探究了采用双点火、降低压缩比以及使用CO2辅助喷射对航空煤油发动机的性能及爆震抑制的影响研究。结果表明,采用双点火可以有效提高航空煤油火焰传播速率,提高燃烧相位,降低循环波动,并且有抑制爆震的作用;通过降低压缩比有效实现了爆震抑制,解决在较高压缩比下航空煤油发动机只能运行在小负荷区间的难题,压缩比降至6,发动机实现全负荷运行,动力性、经济性较好,且不易发生爆震;采用CO2辅助航空煤油喷射时,随着CO2脉宽的增加,同一点火时刻下,发动机的动力性经济性下降,但由于CO2的抑制爆震的作用,MBT点火时刻最大可提前至14 °CA BTDC,使得燃烧相位提前,发动机燃烧效率提高。     

不同掺氢比的HCNG燃料对天然气发动机怠速性能影响研究

为了研究在天然气中掺入不同体积比氢气对发动机怠速性能的影响,针对一台6缸天然气发动机开展了不同体积掺氢比的氢气/天然气混合燃料(HCNG)的怠速性能试验研究.试验证实掺氢后热效率提高,要达到相同的怠速转速可减少怠速旁通阀开度;在怠速情况下,掺氢使CH4、CO、NMHC排放下降,Nox排放上升,可通过点火提前角推迟来有效降低怠速Nox排放;在天然气中掺入适量氢气后有利于改善发动机怠速燃烧,从而增加怠速稳定性.在怠速条件下,掺氢后CO、CH4排放随转速升高先减小后增加;怠速转速升高,怠速稳定性变好.在天然气中掺入适量氢气后,发动机热效率提高,经济性改善.     

电控LPG发动机稀燃技术影响因素的试验研究

针对某小型单缸汽油机进行了LPG化改造,介绍了系统的组成并开发了发动机试验控制系统用于LPG发动机稀薄燃烧技术的研究.研究结果表明:不同的燃烧室形式对稀燃热效率和NOx排放水平具有重要影响,在稀燃状态下直口碗型燃烧室比浅碗型燃烧室的排放性和经济性好.发动机的转速、负荷、压缩比、点火提前角以及火花塞间隙等运转或结构参数是影响LPG发动机稀燃极限的主要因素,负荷和转速提高以及压缩比和火花塞间隙增加,均使稀燃界限拓宽;合理的点火提前角也有利于稀限拓宽;通过对各参数的优化可以拓展LPG发动机的稀燃极限,在保持LPG发动机低排放的情况下可将发动机的动力性基本恢复到原汽油机的水平.     

天然气掺氢发动机的性能研究

以台架试验的方法,对不同负荷与点火提前角下天然气掺氢发动机的经济性和排放特性进行了研究,试验中使用了掺氢比为0%～40%的天然气掺氢混合燃料。试验结果表明,随着掺氢比的增加,燃气消耗率呈降低趋势,发动机的经济性得到明显的改善;在不同负荷下,随着掺氢比的增加,NOx与CO的排放都呈增加趋势,CH4的排放呈降低趋势。掺氢比一定时,随着点火提前角和掺氢比的增加,NOx、CH4与CO排放都呈增加趋势,优化点火提前角可以改善天然气发动机的排放。     

不同点火提前角时HCNG发动机的燃烧与排放特性

在一台火花点火天然气发动机上开展了在不同点火提前角下燃用不同体积掺氢比(O%～50%)的天然气掺氢燃料(HCNG)的试验研究,进行热效率、燃烧放热率、循环变动及排放特性的分析.结果表明:与原天然气发动机相比,HCNG发动机的最大扭矩点火提前角(MB了)减小,MBT时指示热效率变化不大;点火提前角增大时,火焰发展期增长,最大压力变动率减小,快速燃烧期和平均指示压力变动率先减小后增大;在相同点火提前角时,以上4个参数均随掺氢比的增加而减小.N0x、CO排放浓度随掺氢比增加而增大,CH4排放則相反.     

基于AVL_BOOST的氢发动机燃烧特性和性能分析

基于AVL发动机专用数值模拟软件BOOST,建立了单缸直喷氢发动机模型.模拟结果和实验结果的对比表明,所建BOOST模型具有较高的可信度.通过改变发动机的主要结构参数和运转参数,研究氢发动机的燃烧特性以及它们对氢发动机动力性和经济性的影响.     

天然气发动机掺氢20%时瞬态排放性能研究

对天然气发动机掺氢20%(体积比)的瞬态性能进行了研究.主要研究包括不同催化器ETC循环排放的对比、不同加速加浓因子的排放对比以及20%天然气掺氢发动机(HCNG)与纯天然气发动机的排放对比.试验结果表明:三种催化器都能使天然气掺氢发动机排放达到环境友好型汽车标准.随着加速加浓因子的增大,发动机扭矩跟随性越好,但会造成各种排放同时上升,特别是Nox上升幅度很大.三种氧化型催化转化器转化效率大小排序为:ECOCATⅡ型>国产催化器>ECOCATⅠ型.对于这三种催化器来说,随着催化效率的提高,排气阻力加大,发动机动力性下降,燃料消耗率上升.掺入20%氢气后,在不带催化器的情况下,Nox、CO、NMHC、CH4排放和燃料消耗率相对于原天然气发动机分别下降51%、36%、60%、47%和7%.     

高效Atkinson循环TGDI发动机作为传统动力的研究

基于涡轮增压缸内直喷(TGDI)发动机,采用高几何压缩比和大范围可调的可变气门正时(VVT)机构,选择合适的阿特金森(Atkinson)循环率,在兼顾高负荷动力性的同时降低部分负荷的油耗,以解决阿特金森循环发动机动力性不足的问题。制作样机并进行台架试验,研究了阿特金森循环对发动机换气过程的影响和燃油经济性的改善效果及阿特金森循环对排放和动力性的影响。结果表明:阿特金森循环可以容忍更大的几何压缩比以提升热效率,同时有利于降低部分负荷下的泵气损失并提高低负荷时的燃烧稳定性,可降低油耗、颗粒物排放及高负荷时的爆震倾向;但进气门关闭推迟会严重影响发动机的动力性能,因此需要降低高负荷时的阿特金森循环率并提高增压压力。     

外部EGR技术在高压缩比米勒循环发动机上的试验研究

为兼顾米勒循环发动机高负荷动力性和部分负荷燃油经济性,在高压缩比米勒循环发动机上应用外部EGR技术,通过将发动机的部分废气重新引入气缸实现对部分负荷燃烧过程的优化控制,改善发动机的燃油经济性和排放性能。在一台高压缩比米勒循环发动机上,将不同比率的废气重新引入气缸,探究外部EGR技术对高压缩比米勒循环发动机的性能和排放的影响。研究结果表明:在高压缩比米勒循环发动机上应用外部EGR技术,可有效降低发动机部分负荷下的泵气损失,改善燃油经济性,整车百公里油耗改善2.11%;同时可降低缸内最高燃烧温度及含氧量,大量减少NOx排放,部分工况点甚至可降低88.5%。     

Power output characteristics of hydrogen-natural gas blend fuel engine at different compression ratios

Potential and knocking characteristics of a hydrogen-natural gas blend (HCNG) engine with a high compression ratio were examined from a commercial viewpoint since lean combustion with HCNG under a wide-open throttle (WOT) condition requires a high-charging-capacity turbocharger. Supercharging of intake air to extend the lean limit was investigated for a turbocharged, heavy-duty natural gas-fueled engine. Effects of compression ratio changes on fuel economy were assessed in terms of thermal efficiency and torque characteristics. Extension of the lean limit to an excess air ratio of 1.8 for an HCNG engine under WOT conditions is realizable using a supplementary supercharging system. Thermal efficiency improvement at high compression ratios is reduced under relatively rich mixture conditions because spark timing is retarded to avoid knocking. The excess air ratio corresponding to maximum thermal efficiency decreases to 1.6 for an HCNG engine due to the decrease in exhaust gas energy for intake-air charging.     

The effect of hydrogen on the performance and emissions of an SI engine having a high compression ratio fuelled by compressed natural gas

The aim of this paper is investigation of the effect of hydrogen on engine performance and emissions characteristics of an SI engine, having a high compression ratio, fuelled by HCNG (hydrogen enriched compressed natural gas) blend. The experiments were carried out at 1500, 2000 and 2500 rpm under full load conditions of a modified Isuzu 3.9 L engine, having a compression ratio of 12.5. The engine brake power, brake thermal efficiency, combustion analysis and emissions parameters were realized at 5, 10 15 and 20 deg. CA BTDC (crank angle before top dead center) ignition timings and in excess air ratios of 0.9–1.3 fuelled by hydrogen enriched compressed natural gas (100/0, 95/5, 90/10 and 80/20 of % natural gas/hydrogen).The experimental results showed that the maximum power values were generally obtained with HCNG5 (5% hydrogen in natural gas) fuel. The optimum ignition timing that was obtained according to the maximum brake torque was retarded by the addition of hydrogen to CNG (compressed natural gas), while it was advanced by increasing the engine speed. Furthermore, it was observed that the BTE (brake thermal efficiency) generally declined with the hydrogen addition to compressed natural gas and increasing the engine speed. Additionally, the curves of cylinder pressure and ROHR (rate of heat release values) generally closed to top dead center with the increasing of the hydrogen fraction in the blend and a decreasing engine speed. The hydrocarbon and carbon monoxide emissions generally obtained were lower than the Euro-5 and Euro-6 standards.     

The effect of EGR and hydrogen addition to natural gas on performance and exhaust emissions in a diesel engine by AVL fire multi-domain simulation,GPR model,and multi-objective genetic algorithm

In this study, the effect of adding hydrogen to natural gas and EGR ratio was conducted on a diesel engine to investigate the engine performance and exhaust gases by AVL Fire multi-domain simulation software.For this investigation, a mixture of hydrogen fuel and natural gas replaced diesel fuel. The percentage of hydrogen in blend fuel changed from 0% to 40%. The compression ratio converted from 17:1 to 15:1. The EGR ratios were in three steps of 5%, 10%, and 15%, with different engine speeds from 1000 to 1800 RPM. The Gaussian process regression (GPR) was developed to model engine performance and exhaust emissions. The optimal values of EGR and the percentage of hydrogen in the blend of HCNG were extracted using a multi-objective genetic algorithm (MOGA).The results showed that by increasing EGR, thermal efficiency, the engine power, and specific fuel consumption decreased due to prolongation of combustion length while cumulative heat release increased but, its effect on cylinder pressure is insignificant. Adding hydrogen to natural gas increased the combustion temperature and, consequently NOx. While the amount of CO and HC decreased. The results of GPR and MOGA illustrated that at different engine speeds, the optimum values of EGR and HCNG were 6.35% and 31%, respectively.     

Characterization of HCNG combustion and emission characteristics in a constant volume chamber with a single and a dual spark plug configuration

In an effort to reduce the dependency on crude oil based fuels and to decrease pollutant emissions, hydrogen-CNG (HCNG) attracted a considerable attention with its low HC/CO₂ emission and fast burn rate. In this study, a constant volume chamber with a single spark plug and a dual spark plug configuration was designed to obtain fundamental combustion characteristics of HCNG and to evaluate possible advantages of the dual spark plug over the single spark plug ignition setup. Various mixtures of hydrogen and CNG were systematically experimented to evaluate effects of hydrogen fraction to lean burn limit, combustion pressure, rate of heat release and emission characteristics for both configurations. With the current experimental results, it was clearly demonstrated that an appropriate mixture of HCNG along with a suitable spark plug configuration, could become a promising candidate to replace the crude oil based IC engine fuels to alleviate the dependency on the depleting petroleum resource and to meet the stricter emission regulation.     

Numerical analysis of performance and emissions behavior of a bi-fuel engine with compressed natural gas enriched with hydrogen using variable compression ratio strategy

The increase in the compression ratio reduces the fuel consumption and improves the performance. These effects of compression ratio could be observed in all of the engines, such as compression or spark ignition engines. Moreover, due to the compression ratio constraint based on the knocking phenomenon in spark ignition engines, there will always be an optimal compression ratio, which is one of the most fundamental factors in engine design. The optimum compression ratio could be achieved depending on the type of fuel, but in the case of bi-fuel engines, since the nature of each fuel is different, the design must be relatively optimal for both fuels. In this work, by using the VCR (variable compression ratio) strategy, the bi-fuel EF7 engine performance, combustion, and emissions were investigated in different compression ratios when the engine uses gasoline or HCNG (hydrogen enriched compressed natural gas) as fuel. The results revealed that by changing the compression ratio from 11.05 (actual compression ratio of engine) to 11.80 in HCNG mode, an increase of 13% in power could be achieved. Also CO formation, at the compression ratio of 11.80, was slightly lower (7%) than the compression ratio of 11.05. In addition, by reducing the compression ratio from 11.05 to 10.50 in gasoline mode, there was a significant increase in emissions; that was 44% for the NO_x and 16% for the CO, which could be one of the limiting factors of the advance in spark timing. Moreover, due to the VCR strategy and the significant optimization of the compression ratio, the combinatory method of VCR – HCNG can be used as an effective method for the bi-fuel engines in order to improve the performance and reduce emissions.     

车用发动机燃用天然气掺氢燃料的性能计算分析与研究

为了研究天然气掺氢发动机的燃烧特性,从模拟试验的角度运用大型发动机软件建立了6缸火花点火天然气掺氢发动机的虚拟样机,并经过试验验证该模型基本准确.通过仿真计算得出,天然气发动机在掺入氢气之后,提高了燃烧速度,明显拓宽了发动机的稀燃极限.在掺入氢气30 %(体积百分比)时,发动机的综合性能指标较好;提高压缩比,指示热效率得到提高.     

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.     

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.     

Applying the multi-zone model in predicting the operating range of HCCI engines

In this paper, a multi-zone model is developed to predict the operating range of homogeneous charge compression ignition (HCCI) engines. The boundaries of the operating range were determined by knock (presented by ringing intensity), partial burn (presented by combustion efficiency), and cycle-to-cycle variations (presented by the sensitivity of indicated mean effective pressure to initial temperature). By simulating an HCCI engine fueled with iso-octane, the knock and cycle-to-cycle variations predicted by the model showed satisfactory agreement with measurements made under different initial temperatures and equivalence ratios; the operating range was also well reproduced by the model. Furthermore, the model was applied to predict the operating range of the HCCI engine under different engine speeds by varying the intake temperatures and equivalence ratios. The potential to extend the operating range of the HCCI engine through two strategies, i.e., variable compression ratio and intake pressure boosting, was then investigated. Results indicate that the ignition point can be efficiently controlled by varying the compression ratio. A low load range can be extended by increasing the intake temperature while reducing the compression ratio. Higher intake temperatures and lower compression ratios can also extend the high load range. Boosting intake pressure is helpful in controlling the combustion of the HCCI engine, resulting in an extended high load range.     

增压稀燃天然气掺氢发动机排放特性

为了研究20%掺氢比的增压稀燃天然气掺氢(HCNG)发动机的排放特性,通过对发动机进行了空燃比和点火提前角调整试验、ETC循环测试试验和加装氧化型催化器试验,获得了20%HCNG发动机的排放规律.CH4排放随着空燃比的增大先减少后增加;CO排放在高于理论空燃比后骤减;Nox排放随着空燃比的增大先增加后减少,在空燃比19～21 左右达到最大值,1600～1800r/min时最低.CO、Nox随着点火提前角的增大而增加;CH4随着点火提前角的增大略有增加,并且点火提前角越大,对CH4排放的影响越小.加装催化器后,CO、CH4的转化效率均＞90%.试验结果表明:增压稀燃和氧化型催化器相结合是天然气掺氢发动机节能减排的有效方案.