气体机点火时刻和燃料当量比对气耗影响的研究

研究了天然气(LNG)发动机点火提前角与燃料当量比对燃料消耗率的综合影响,对点火过程的各阶段进行了分析,对不同当量比的混合气燃烧过程进行了对比,通过改变点火提前角和燃料当量比,得到不同工况下发动机的点火提前特性和燃料调整特性,本次试验数据表明:在各工况下,要获得最低的燃料消耗率,点火提前角与燃料当量比均存在一个最佳值,选择较合适的点火提前角与燃料当量比,使天然气发动机可以兼顾低速动力性与高速经济性。     

低压缸内直喷CNG发动机燃烧特性的影响因素

自主研发了低压缸内直喷压缩天燃气(CNG)发动机,研究了过量空气系数、喷气时刻、点火能量、点火时刻等 对发动机燃烧特性的影响.结果表明,喷气时刻对低压缸内直喷CNG发动机的燃烧性能有很大影响,对于给定的工况,发动机存在一个最佳喷气提前角;提高点火能量有助于改善CNG发动机的燃烧过程,增大点火提前角,可以在一定程度上弥补由于天然气燃料火焰传播速度慢所导致的热效率下降,从而改善发动机缸内的燃烧过程,使其功率增加,燃气消耗率降低.     

重型增压预混天然气发动机动力性和排放性试验研究

为解决天然气发动机排放问题,对严重影响天然气发动机HC和NOx排放的空燃比和点火提前角这两个参数进行试验研究。结果表明,增大点火提前角可以提高发动机功率输出,降低有效燃气消耗率和HC排放,增加NOx排放;增大空燃比,发动机功率和NOx排放下降,而有效燃气消耗率和HC排放上升,且均在稀燃极限空燃比时急剧变化。     

利用EGR控制甲醇发动机负荷

将一台2,L柴油机改装成点火式甲醇发动机,在该发动机上做了仅利用EGR(废气再循环)控制负荷的试验研究.试验时节气门全开,仅用废气和甲醇喷射量来调节负荷.试验中选择了多个点火提前角,寻找了每个点火提前角下的爆震对应的最小EGR率和转矩波动对应的最大EGR率,以及利用EGR可控的负荷范围.结果显示,在18,°CA BTDC点火时最大转矩达到153.4,N.m,在39,°CA BTDC点火时最小转矩达到55.5,N.m;点火提前角增大,最小EGR率逐渐增大,最大EGR率先增大后减小;点火提前角增大,最大转矩逐渐降低,最小转矩先增大后减小,且中间有波动;通过油耗分析,发现功率在14,kW以上,可以通过调整点火提前角来降低燃料消耗率,而功率小于14,kW之后通过调整点火提前角降低燃料消耗率不明显.     

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。     

汽油机点火提前调整特性模拟分析

论文利用AVL Boost建立了四缸四冲程汽油机的热力学仿真模型,并从气缸压力的变化及缸内气流运动的角度出发,分析了点火提前角对最高燃烧压力的影响,从而确定各转速下的点火提前角变化范围.在此基础上进一步分析了点火提前角对汽油机动力性及经济性的影响,以期确定较为合理的点火提前特性匹配方案.分析结果显示:随着转速的增加,增大点火提前角,有利于提高发动机的动力性和燃油经济性;合理的匹配不同转速下的点火提前角,可扩大汽油机的理想工作范围.     

压缩天然气发动机的设计及性能研究

为提升压缩天然气(CNG)发动机的综合性能,从考察、研究压缩天然气理化特性的角度出发,选择在一款柴油机原型机上改装天然气发动机,为天然气发动机设计燃料供给系统、进气系统、点火系统、燃烧系统以及后处理系统,以满足压缩天然气在发动机上的相关燃用要求。对改装设计的压缩天然气发动机开展台架试验研究,分析压缩天然气发动机的负荷特性、速度特性以及万有特性,并综合评价改装后的压缩天然气发动机性能表现。研究结果表明:相比于柴油机原机,改装设计的压缩天然气发动机最大转矩提高约22%,动力性增强;同时最小等热值有效燃油消耗率下降约2%,经济性获得改善;且压缩天然气发动机的升功率和比功率提升,发动机强化程度提高。     

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。     

火花点火天然气发动机起动阶段HC排放特性研究

为降低天然气发动机起动阶段的HC排放,在一台6缸火花点火天然气发动机上进行了起动试验研究。控制起动阶段的喷射脉宽和点火提前角,采集起动后1min内的转速和排放数据。试验结果表明:在一定范围内,HC排放随喷射脉宽和点火提前角的增加而增加。为保证顺利起动并有较低的HC排放,起动初始阶段应采用较大的喷射脉宽和较大的点火提前角,而转速稳定后采用逐渐减小的喷射脉宽和点火提前角。     

不同喷射时刻下缸内直喷天然气发动机的燃烧特性

开展了天然气高压缸内直喷发动机不同喷射时刻时的燃烧特性研究。研究结果表明：燃料喷射时刻对发动机性能及排放有较大影响，喷射太迟会导致天然气和空气混合时间短，混合效果差，燃烧持续期长，放热速率慢。喷射过早会导致充量系数下降，燃料容易进入燃烧室狭缝间隙处，造成较高的HC排放。对于给定转速，发动机存在一个最佳燃料喷射提前角，此时缸内最高压力值最大，最大压力升高率和最大放热率最大，放热速率快，燃烧过程等容度好，火焰发展期、快速燃烧期和燃烧持续期短，发动机热效率高，HC、CO排放也维持较低水平。     

Simulation of a hydrogen/natural gas engine and modelling of engine operating parameters

At the present work for improving the engine performance and decrease of emissions, a port injection gasoline engine is converted into direct injection. Engine performance behavior was investigated by AVL Fire software with adding hydrogen to natural gas from 0% up to 30%. Validation of the simulated model and experimental results show good confirmation. To determine the relationship between independent variables engine speed, ignition timing, injection timing and H₂% versus the dependent variables including engine performance parameters, specific fuel consumption, CO and statistical analysis models were used. Comparison between different errors models shows that Radial basis function model with training algorithm Bayesian regularization back propagation can estimate better engine performance variables. The results showed that adding hydrogen to natural gas cause the output power, torque, fuel consumption efficiency increase and specific fuel consumption drop. Also, CO decreases when ignition and injection timing be advanced and engine speed reaches to its largest.     

推迟供油提前角对生物柴油发动机燃烧和排放性能的影响

在直喷式增压柴油机上进行了供油提前角对生物柴油发动机动力性、经济性和排放性能影响的研究。试验结果表明:与柴油相比,推迟供油提前角后生物柴油的动力性下降,燃油经济性恶化,NO_x和烟度排放均有不同程度的降低。推迟供油提前角对生物柴油的喷油压力和滞燃期影响不大,但喷油始点和燃烧始点均迟于柴油。与柴油相比,推迟供油提前角后最高气缸压力下降,放热峰值出现时刻提前,指示热效率降低。燃烧始点与NO_x排放的相关性最大,喷油始点和放热峰值出现时刻也与NO_x排放呈弱相关性。     

F-T柴油对直喷式柴油机燃烧和排放的影响

在两种不同供油提前角下研究了燃用F-T柴油对直喷式柴油机燃烧和排放特性的影响,结果表明:发动机不做任何调整时,与0号柴油相比,燃用F-T柴油的滞燃期较短,预混燃烧放热峰值较低,扩散燃烧放热峰值较高,最高燃烧压力和最大压力升高率较低,燃油消耗率和热效率都得到了改善,HC、CO、NOx和碳烟排放同时降低。当供油提前角推迟3℃A时,燃用F-T柴油燃烧持续期明显缩短,预混燃烧放热峰值、最高燃烧压力和最大压力升高率进一步降低,扩散燃烧放热峰值略有升高,燃油消耗率变化不大,NOx排放进一步降低, HC、CO和碳烟略有增加,其中HC排放与原柴油机相当,而CO和碳烟仍远低于原柴油机。     

生物制气-柴油双燃料发动机放热规律试验研究

采用气化炉热解气化各种农林废弃的生物质，产生可燃生物制气，用作为以柴油引燃的双燃料发动机的主要燃料。测量生物制气-柴油双燃料发动机气缸压力，计算分析放热规律。双燃料发动机与燃用纯柴油时的发动机相比，燃烧始点延迟，最大燃烧压力降低，最大放热率和排气温度增加，后燃较严重。负荷增大时，双燃料发动机燃烧始点提前，最大燃烧放热率增高，最高燃烧温度升高，后燃较严重。供油提前角提前时，后燃减小，燃烧过程明显改善。     

Effects of Fischer-Tropsch diesel fuel on combustion and emissions of direct injection diesel engine

Effects of Fischer-Tropsch (F-T) diesel fuel on the combustion and emission characteristics of a single-cylinder direct injection diesel engine under different fuel delivery advance angles were investigated. The experimental results show that F-T diesel fuel exhibits shorter ignition delay, lower peak values of premixed burning rate, lower combustion pressure and pressure rise rate, and higher peak value of diffusion burning rate than conventional diesel fuel when the engine remains unmodified. In addition, the unmodified engine with F-T diesel fuel has lower brake specific fuel consumption and higher effective thermal efficiency, and presents lower HC, CO, NO_x and smoke emissions than conventional diesel fuel. When fuel delivery advance angle is retarded by 3 crank angle degrees, the combustion duration is obviously shortened; the peak values of premixed burning rate, the combustion pressure and pressure rise rate are further reduced; and the peak value of diffusion burning rate is further increased for F-T diesel fuel operation. Moreover, the retardation of fuel delivery advance angle results in a further significant reduction in NO_x emissions with no penalty on specific fuel consumption and with much less penalty on HC, CO and smoke emissions.     

Effect of advanced injection timing on the performance of rapeseed oil in diesel engines

Combustion studies on both diesel fuel and vegetable oil fuels, with the standard and advanced injection timing, were carried out using the same engine and test procedures so that comparative assessments may be made. The diesel engine principle demands self-ignition of the fuel as it is injected at some degrees before top dead centre (BTDC) into the hot compressed cylinder gas. Longer delays between injection and ignition lead to unacceptable rates of pressure rise with the result of diesel knock because too much fuel is ready to take part in premixed combustion. Alternative fuels have been noted to exhibit longer delay periods and slower burning rate especially at low load operating conditions hence resulting in late combustion in the expansion stroke. Advanced injection timing is expected to compensate these effects. The engine has standard injection timing of 30°C BTDC. The injection was first advanced by 5.5°C given injection timing of 35.5°C BTDC. The engine performance was very erratic on this timing. The injection was then advanced by 3.5°C and the effects are presented in this paper. The engine performance was smooth especially at low load levels. The ignition delay was reduced through advanced injection but tended to incur a slight increase in fuel consumption. Moderate advanced injection timing is recommended for low speed operations.     

Hydrogen and propane implications for reactivity controlled compression ignition combustion engine running on landfill gas and diesel fuel

A detailed investigation of employing landfill gas together with additives such as hydrogen or propane or both as a primary low reactivity fuel in a reactivity controlled compression ignition combustion of a diesel engine is conducted. A 3401E caterpillar single-cylinder diesel engine with a bathtub piston bowl profile is utilized to execute the study. The engine is operated at various intake pressures of 1.6, 1.9, and 2.2 bar, and runs at a fixed engine speed of 1300 rpm. For verification purposes, the conduct of the present engine running on pure methane as a low reactivity fuel is compared to that of the same engine available in the literature. Next, a numerical simulation is made to assess the performance of the present engine running on landfill gas plus the additives. Based on the obtained results, injecting either hydrogen or propane or a combination of both up to a total amount of 10% by volume to the premixed of landfill gas and air, and advancing diesel fuel injection timing of about 20–30 deg. crank angle, render the landfill gas utilization quite competitive with using methane alone. Applying an enriched landfill gas in a reactivity controlled compression ignition diesel engine, as a power generator, drastically reduces the greenhouse gas emission to the atmosphere. Also, the CO and UHC mole fraction in the exhaust gas can be eliminated by either advancing the start of diesel injection or using hydrogen or propane or both as additives. In addition, utilizing hydrogen or propane or a combination of both with the primary fuel improves the peak pressure to about 16% in comparison with that of landfill gas alone.     

柴油机TR燃烧系统实现低温预混合燃烧的研究

为了验证TR燃烧系统降低发动机排放、实现低温预混合燃烧的能力,在一台经过改造的单缸135柴油机上进行了降低压缩比、燃用柴油-乙醇混合燃料和推迟供油的试验研究.结果表明,压缩比ε降低后,着火推迟,最大放热率增加,缸内最高压力和最高温度降低,NOx排放也降低.但是中高负荷时燃烧速率降低,有效油耗率增加.当燃用乙醇体积含量20%的乙醇-柴油混合燃料时,与燃用柴油燃料相比,着火延迟期延长,烟度大幅度降低.小负荷时缸内最高压力、最高温度、最大放热率和燃烧速率都降低,NOx降低较多;中高负荷时最大放热率高于后者,燃烧速率提高,NOx降低得较少.当供油定时从15°CA BT-DC推迟到13°CA BTDC后,烟度基本不变.     

废气再循环率及点火时刻对天然气发动机燃烧和排温的影响

基于一台当量比燃烧的天然气发动机,采用三维燃烧分析与发动机一维热力学计算相结合的方式开展了废气再循环(exhaust gas recirculation,EGR)率及点火时刻对缸内燃烧过程和发动机排温的影响研究。研究结果表明:随着EGR率的增加,燃烧相位后移,燃烧持续期延长,放热率峰值减小,最大压升率、缸内最高燃烧压力和最高平均燃烧温度均降低,再循环废气的稀释作用和热容效应能够抑制混合气的燃烧。随着点火时刻的提前,燃烧重心(CA50)前移,燃烧持续期缩短,最大压升率、缸内压力和放热率峰值均增大。排温随EGR率的增大和点火时刻的提前而降低。保持空气和燃气进气量不变,EGR率增大至23%,点火时刻提前至-18°能够将原机标定功率提升7.4 kW,有效燃料消耗率降低4 g/(kW·h)。当空气和燃气进气量增加11.6%,EGR率大于19%,点火时刻早于-10.5°时,可将原机标定功率提升36 kW并且将排温控制在760℃以内。     

Performance evaluation of a constant speed IC engine on CNG,methane enriched biogas and biogas

This paper presents the performance results of a 5.9 kW stationary diesel engine which was converted into spark ignition mode and run on compressed natural gas (CNG), methane enriched biogas (Bio-CNG) and biogas produced from biomethanation of jatropha and pongamia oil seed cakes. The performance of the engine with 12.65 compression ratio was evaluated at 30°, 35° and 40° ignition advance of TDC. The maximum brake power produced by the engine was found at ignition advance of 35° TDC for all the tested fuels. In comparison to diesel as original fuel, the power deteriorations of the engine was observed to be 31.8%, 35.6% and 46.3% on compressed natural gas, methane enriched biogas and raw biogas, respectively, due to its conversion from CI to SI mode. The methane enriched biogas showed almost similar engine performance as compared to compressed natural gas in terms of brake power output, specific gas consumption and thermal efficiency.