共查询到20条相似文献,搜索用时 31 毫秒
1.
Q. Fan J. Bian H. Lu L. Li J. Deng 《International Journal of Automotive Technology》2012,13(4):523-531
The first firing cycle is very important during cold-start for all types of spark ignition engines. In addition, the combustion characteristics of the first firing cycle affect combustion and emissions in the following cycles. However, the first-cycle fuel-air mixing, combustion and emissions generation within the cylinder of a two-stage direct-injection (TSDI) engine during cold start is not completely understood. Based on the total stoichiometric air-fuel ratio and local richer mixture startup strategy, the first-cycle firing and combustion characteristic at cold start were investigated in a two-stage direct injection (TSDI) gasoline engine. In addition, the effects of the first injection timing, second injection timing, 1st and 2nd fuel injection proportion and total excess air ratio on the in-cylinder pressure, heat release rate and accumulated heat release were analyzed on the basis of a cycle-by-cycle analysis. It is shown that a larger 2nd fuel injection amount and later 2nd injection timing are more beneficial to the firing of the first cycle in the case of a total excess air ratio of 1.0. The optimum 1st and 2nd injection timing fuel injection proportions are 120°CA ATDC during the intake stroke, 60°CA BTDC during the compression stroke and 1:1. In addition, the firing boundary is a 2nd injection timing later than 90°CA BTDC during the compression stroke in the case of the 1st injection timing from 60°CA to 180°CA ATDC during an intake stroke and involves a 1st and 2nd fuel injection proportion of 1:1 and an excess air ratio of 1.0. The study provides a detailed understanding of cold-start combustion characteristics and a guide for optimizing the reliable first-cycle firing at cold start. 相似文献
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G. T. Chala A. R. A. Aziz F. Y. Hagos 《International Journal of Automotive Technology》2017,18(1):85-96
There is an increasing interest in supercharging spark ignition engines operating on CNG (compressed natural gas) mainly due to its superior knock resisting properties. However, there is a penalty in volumetric efficiency when directly injecting the gaseous fuel at early and partial injection timings. The present work reports the combined effects of a small boost pressure and injection timing on performance and combustion of CNG fueled DI (direct injection) engine. The experimental tests were carried out on a 4-stroke DI spark ignition engine with a compression ratio of 14. Early injection timing, when inlet valves are still open (at 300°BTDC), and partial injection timing, in which part of the injection occurs after the inlet valves are closed (at 180°BTDC), were varied at each operating speed with variation of the boost pressure from 2.5 to 10 kPa. A narrow angle injector (NAI) was used to increase the mixing rate at engine speeds between 2000 and 5000 rpm. Similar experiments were conducted on a naturally aspirated engine and the results were then compared with that of the boosting system to examine the combined effects of boost pressure and injection timing. It was observed that boost pressure above 7.5 kPa resulted in an improvement of performance and combustion of CNG DI engine at all operating speeds. This was manifested in the faster heat release rates and mass fraction burned that in turn improved combustion efficiency of the boosting system. An increased in cylinder pressure and temperature was also observed with boost pressure compared to naturally aspirated engine. Moreover, the combustion duration was reduced due to concentration of the heat release near to the top dead center as the result of the boost pressure. Supercharging was also found to reduce the penalty of volumetric efficiency at both the simulated port and partial injection timings. 相似文献
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环境对大功率柴油机缸内喷雾、燃烧与传热的影响 总被引:2,自引:0,他引:2
采用准维多区数值仿真和环境模拟试验的方法,研究了不同海拔环境对某大功率柴油机缸内喷雾、燃烧和传热的影响。结果表明:在高原环境下,油核破裂滞后期比平原最大延长9.1°曲轴转角,油滴分裂长度增加29%以上,贯穿度明显增加,一次雾化后,SMD直径显著增加;海拔4 500m,瞬时放热率峰值降低18.4%,放热率重心后移近4°,最高燃烧压力降低18.8%,位置滞后0.6°;缸内对流换热和辐射换热都比平原明显增强。研究结果为探明特殊环境下柴油机性能劣化与故障机理提供了理论参考。 相似文献
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通过台架试验的方法,对1台0.5L单缸柴油机进行了热力学分析,将缸内燃烧所释放能量的热量分布和可用能分布进行计算和比较,在此基础之上比较了喷油规律相关参数对热平衡的影响,提出了相应减少不可逆损失、提升热效率的解决途径。试验结果表明:在相同工况下,对于不同的喷油模式,燃烧不可逆损失差异不大,差异主要体现在排气损失和其他部分损失;预喷参数和后喷参数对热量分布影响较小,而喷油压力和主喷正时的影响较为明显。随着喷油压力的增大或主喷正时的提前,燃烧不可逆程度降低,排气可用能损失减少,热力循环的热效率得以提升。而对于余热能回收,排气中流失的可用能回收的潜力和价值较大,将这一部分能量妥善地利用可对整机性能起到明显的改善效果,若排气温度从750K降至500K,通过排气余热能的利用可提升指示功20.91%,达到提升动力性和燃油经济性的目的。 相似文献
5.
J. H. Jeong D. W. Jung O. T. Lim Y. D. Pyo Y. J. Lee 《International Journal of Automotive Technology》2014,15(6):861-869
This work experimentally investigates how the dwell time between pilot injection and main injection influences combustion and emissions characteristics (NOx, CO, THC and smoke) in a single-cylinder DI diesel engine. The experiments were conducted using two fuel injection systems according to the fuel type, diesel or dimethyl ether (DME), due to the different fuel characteristics. The injection strategy is accomplished by varying the dwell time (10°CA, 16°CA and 22°CA) between injections at five main injection timings (?4°CA aTDC, ?2°CA aTDC, 0°CA aTDC, 2°CA aTDC and 4°CA aTDC). Results from pilot-main injection conditions are compared with those shown in single injection conditions to better demonstrate the potential of pilot injection. It was found that pilot injection is highly effective for lowering heat-release rates with smooth pressure traces regardless of the fuel type. Pilot injection also offers high potential to maintain or increase the BMEP; even the combustion-timing is retarded to suppress the NOx emission formation. Overall, NOx emission formation was suppressed more by the combustion phasing retard effect, and not the pilot injection effect considered in this study. Comparison of the emissions for different fuel types shows that CO and HC emissions have low values below 100 ppm for DME operation in both single injection and pilot-main injection. However, NOx emission is slightly higher in the earlier main injection timings (?4°CA aTDC, ?2°CA aTDC) than diesel injections. Pilot injection was found to be more effective with DME for reducing the amount of NOx emission with combustion retardation, which indicates a level of NOx emission similar to that of diesel. Although the diesel pilot-main injection conditions show higher smoke emission than single-injection condition, DME has little smoke emission regardless of injection strategy. 相似文献
6.
Recently, to reduce environmental pollution and the waste of limited energy resources, there is an increasing requirement
for higher engine efficiency and lower levels of harmful emissions. A premixed charge compression ignition (PCCI) engine,
which uses a 2-stage type injection, has drawn attention because this combustion system can simultaneously reduce the amount
of NOx and PM exhausted from diesel engines. It is well known that the fuel injection timing and the spray angle in a PCCI
engine affect the mixture formation and the combustion. To acquire two optimal injection timings, the combustion and emission
characteristics of the PCCI engine were analyzed with various injection conditions. The flame visualization was performed
to validate the result obtained from the engine test. This study reveals that the optimum injection timings are BTDC 60° for
the first injection and ATDC 5° for the second injection. In addition, the injection ratio of 3 to 7 showed the best NOx and
PM emission results. 相似文献
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大气压力和冷却液温度对柴油机性能影响的试验研究 总被引:1,自引:0,他引:1
利用内燃机高海拔(低气压)模拟试验系统,研究了大气压力和冷却液温度对柴油机性能与燃烧特性的影响规律。试验结果表明:随着进气压力降低,柴油机最高燃烧压力下降,缸内平均温度大幅升高,燃烧始点推迟且持续期延长,后燃严重,燃烧过程未能及时释放热量,动力性能和燃料经济性下降明显;随着冷却液温度的升高,最高燃烧压力增大,燃烧始点提前且持续期略有延长,燃烧重心略微前移,燃烧放热率减小,且大气压力越低冷却液温度对柴油机燃烧过程的影响越明显。在高海拔(低气压)条件下,提高柴油机冷却液工作温度,可以明显减少冷却液散热量,提高柴油机的热-功转换效率,显著改善柴油机的高原动力性和经济性,同时柴油机热负荷升高幅度并不大。 相似文献
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提出了一种新的压燃式天然气发动机燃烧系统,采用CFD软件对不同燃烧室几何参数下的缸内湍流场进行了模拟计算。结果表明,通道直径从8 mm增加到14 mm时,燃烧室内湍动能有所减少,但湍动能分布变得更加均匀,且副室中心区域的湍动能增加;通道倾角从40°增大到60°时,副室内中心区域的湍动能增加;此外,通道位置和副燃烧室形状对湍流运动也有一定的影响。 相似文献
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本文提出一种能够实现三维可视化的燃烧室内燃油分布和喷雾着壁特性计算的方法。该方法可适于任意形状的燃烧室,能反映出喷油压力,喷油嘴结构及安装位置,进气涡流比等参数与燃烧室形状的匹配关系。对采用梅花型缩口燃烧室的CA6110型柴油机,进行了计算分析及实验研究,对本文的方法进行了验证。 相似文献
13.
缸内直喷醇类燃料发动机的燃烧与排放特性 总被引:2,自引:0,他引:2
根据所测的示功图和排放,分析了一台采用火花点火、缸内直喷周向分层燃烧系统的发动机在燃用甲醇和乙醇时的性能和燃烧特性。研究表明,醇类燃料发动机的燃烧由预混燃烧与扩散燃烧组成,具有非常快的燃烧速率,而且非常稳定,ATDC(3°CA~6°CA)就燃烧完50%燃料,循环变动小于6%。与燃用乙醇相比,燃用甲醇时滞燃期较短,燃烧速率较快。由于采用分层燃烧,醇类燃料发动机具有与直喷柴油机相当的热效率,在负荷特性上,燃用醇类燃料时的NOx排放仅为柴油机的10%~40%,且能实现无烟燃烧,CO排放的增加低于1%,HC排放高于柴油机。 相似文献
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在1台排量为2.8L的单缸柴油机上,通过燃烧过程不断强化,将输出功率从73kW提高到150kW。研究分为两个阶段:第一阶段通过提高进气压力、降低进气阻力、优化配气相位、优化喷油系统参数,将输出功率从73kW提高到92kW;第二阶段采用了电控单体泵供油系统,并优化喷孔参数、进一步提高进气压力、降低进气温度、提高发动机转速,将输出功率提高到150kW。放热率分析结果表明:对于高强化燃烧过程,虽然预混和扩散燃烧阶段的放热速率大幅度增加,但其放热量占总放热量的比率下降,后燃阶段的放热比率显著增加。因此加强扩散燃烧阶段的放热速率仍然是高强化燃烧过程面临的主要问题。 相似文献
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针对生产中实际问题,对现生产的CA6102发动机燃烧系统进行了改进设计,并在单缸机台架上采用CB-466发动机燃烧分析仪等测试仪器,对改进设计的燃烧系统燃烧过程进行了测试与分析。经改进设计,发动机燃烧过程得到较好的改善,动力性提高,燃油消耗率下降,且生产时无需更改加工设备,生产上易于实现。 相似文献
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点火时刻对甲醇发动机燃烧及非法规排放的影响 总被引:2,自引:1,他引:1
针对甲醇发动机低温冷起动困难,在1台由1130单缸柴油机改造而成的直喷火花点火甲醇发动机上,利用CFD模拟软件AVL-Fire耦合甲醇氧化反应机理,通过电热塞将进气温度加热到283K,研究了点火时刻对甲醇发动机低温(266K)冷起动燃烧及非法规排放的影响。结果表明:提前点火时刻能够使缸内混合气得到较充分燃烧,减少未燃甲醇排放,当点火时刻由8°BTDC提前到11°BTDC时未燃甲醇排放显著减少;提前点火时刻能够降低甲醛排放,当点火时刻提前到17°BTDC、缸内最高燃烧温度超过1 300K时,甲醛快速氧化,甲醛排放显著减少。 相似文献
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An electric water pump for engine cooling system has an advantage which particularly in the cold start, the use of the electric water pump saves fuel and leads to a corresponding reduction in emissions. However, the electric water pump for internal combustion engine generates much more heat loss than that for hybrid electric vehicle or electric vehicle since it is operated by electric power of high current and low voltage. In this study, the fluid flow and thermal characteristics of the canned type electric water pump with an inverter integrated has been investigated under the effects of heat generation. The analysis conditions such as outdoor air temperature of 125°C, water pump speed of 6000 rpm, coolant temperature of 106°C and coolant flow rate of 120 L/min were used as a standard condition. Therefore, the thermal performance of the canned type electric water pump’s motor and inverter was evaluated by comparison with that of mechanical seal type. In the motor, the temperature reduced by over 10°C, and in the inverter, the amount of temperature decrease equaled to the maximum temperature difference, about 18.7°C. Also, canned type electric water pumps of variable materials were compared for the evaluation of thermal transfer performance for variable thermal conductivity of a can. The motor and inverter were cooled lower to 42°C at motor and about 40°C at inverter for reasonable selection of can’s thermal conductivity. 相似文献
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M15甲醇柴油的燃烧过程及循环变动分析 总被引:1,自引:0,他引:1
通过增压中冷柴油机燃用M15甲醇柴油混合燃料的台架试验,研究了外部EGR对柴油机燃烧过程及循环变动的影响。结果表明:与燃用0号柴油比,原机燃用M15甲醇柴油工作柔和,循环波动小。低转速低负荷时宜采用小EGR率,滞燃期短,放热重心基本不变,循环波动小;中等负荷时可采用大EGR率,随着EGR率的增大,滞燃期延长,放热重心推后,最大燃烧压力循环变动率稍有上升,平均指示压力和最大压力升高率波动大幅降低。经相关性分析,低转速中低负荷下,滞燃期对循环波动影响较小,放热重心与最大压力升高率有着很好的线性关系。 相似文献