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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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The sub-chamber type gasoline engine was suggested to be a type of clean engine, but the presence of residual gas in the sub-chamber
was a serious fault. In this experimental study, the CNG direct injection method was applied to scavenge residual gas from
the sub-chamber. The CVC (constant volume chamber) is divided into the sub-chamber and main-chamber and used as the main experimental
apparatus. Because each combustion chamber of the CVC has an injector, the injector can be used freely, at the same time or
individually. Therefore, the scavenging efficiency can be improved by changing injection times for the sub-chamber. The experimental
results demonstrated that when all the fuel was injected into the sub-chamber, the combustion duration was shortened by 30%
compared to that of injection into the main-chamber. Although residual gas was observed in the CVC, when the frequency of
injections into the sub-chamber increased, good combustion characteristics were obtained. 相似文献
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For several decades, the primary goal of the automotive industry has been to reduce harmful emissions and improve fuel economy.
Gasoline engines are clean and powerful propulsion systems, but have poorer fuel economy than that of diesel engines. However,
due to the development of new technologies such as variable valve timing and lift and direct gasoline injection, controlled
autoignition (CAI) combustion can be realized. CAI engines combine the advantages of cleaner emissions and lower fuel consumption
than conventional spark-ignition gasoline engines. In this study, a cylinder-pressure-based combustion phase detection method
for CAI combustion is proposed. This method utilizes a normalized difference pressure (NDP), which is defined as the normalized
pressure difference between the firing and motoring in-cylinder pressures. The proposed method was developed and validated
with steady-state experimental data from an inline 4 cylinder, 2 L gasoline direct injection (GDI) CAI engine. Because the
calculations in the NDP method are faster and simpler than in the conventional combustion phase detection method in CAI engines,
this method can be embedded in a real-time controller. Furthermore, the proposed method displayed good accuracy in detecting
the combustion phase and thus stabilized CAI combustion. Finally, the detailed experimental results are presented. 相似文献
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We investigated the effects of the fuel injection timing — both for early and late injection — in conjunction with the throttle
opening ratio on the fuel-air mixing characteristics, engine power, combustion stability and emission characteristics of a
DI CNG spark engine and control system that had been modified and designed according to the author’s original idea. We verified
that the combustion characteristics were affected by the fuel injection timing and that the engine conditions were affected
by the throttle opening ratios and the rpm. The combustion characteristics were greatly improved for a complete open throttle
ratio with an early injection timing and for a partial throttle ratio with a late injection timing. The combustion duration
was governed by the duration of flame propagation in late injection timing scenarios and by the duration of early flame development
in cases of early injection timing. As the result, the combustion duration is shortened, the lean limit is improved, the air-fuel
mixing conditions are controlled, and the emissions are reduced through control of the fuel injection timing and vary according
to ratio of the throttle opening. 相似文献
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国内外燃气汽车发动机研究动向 总被引:3,自引:0,他引:3
通过对燃气汽车发动机供气方式的试验研究以及对国内外在燃气发动机领域研究成果的分析,阐述了影响燃气汽车动力性的因素,指出进气道液态LPG喷射较好地解决了充气效率下降的问题,缸内液态LPG直接喷射效果更佳,是解决LPG发动机动力性下降的有效途径之一。CNG缸内直喷技术从根本上解决了预混合方式中天然气燃料挤占进气空气造成充气效率下降的问题,可有效提高CNG发动机的动力性。LNG纯度高、存储体积小、安全可靠,续驶里程长,比CNG更具发展潜力。 相似文献
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CNG发动机和汽油机燃烧的比较分析 总被引:9,自引:0,他引:9
CNG发动机与汽油机的燃烧同为预混湍流燃烧,但火焰传播速度、着火延迟期及混合气热值均不同。为在汽油机上改燃CNG或CNG/汽油两用燃料发动机发挥CNG燃烧的优点,针对CNG燃烧特点设计发动机,才能达到较高的输出功率和较低的排放。 相似文献
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在一台单缸柴油机上加装天然气电控喷射系统,改造成柴油/CNG双燃料发动机。通过示功图、放热率、排放特性和经济性的实验与分析,研究了纯柴油和双燃料两种燃烧模式下应用冷却EGR的效果。研究表明:不管是纯柴油模式还是双燃料模式,使用EGR之后,NOx都有大幅度降低;纯柴油模式使用EGR之后,会带来碳烟排放的恶化,但是对于双燃料模式,当EGR比例在22%以内,负荷小于75%时,不会造成碳烟排放的恶化。随着EGR比例的增大,燃烧放热率曲线由双峰过渡到单峰形状,具有均质压燃(HCCI)燃烧过程的特征。 相似文献
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在电容储能点火系统的基础上,利用火花能量转换原理和能量叠加原理,提出了一种有别于传统发动机点火系的"稀燃快燃点火系"。简要介绍和分析了该点火系的组成及工作原理,对其进行了设计研究,通过试验验证了稀燃快燃点火系比传统点火系具有的优越性。结果表明:该点火系统能够提高点火线圈的次级电压,增加火花持续时间,有效提高点火能量的利用率,改善发动机点火性能。该点火系在进行适当匹配后不仅适用于现代高速、稀燃、高压缩比发动机,而且也适用于传统点燃式发动机。 相似文献
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A. Broatch J. M. Luján S. Ruiz P. Olmeda 《International Journal of Automotive Technology》2008,9(2):129-140
Most of hydrocarbon (HC) and carbon monoxide (CO) emissions from automotive DI Diesel engines are produced during the engine
warm-up period and are primarily caused by difficulties in obtaining stable and efficient combustion under these conditions.
Furthermore, the contribution of engine starting to these emissions is not negligible; since this operating condition is highly
unfavorable for the combustion progress. Additionally, the catalytic converter is ineffective due to the low engine temperature.
In conjunction with adequate engine settings (fuel injection and fresh air control), either the glow plugs or the intake air
heater are activated during a portion of the engine warm-up period, so that a nominal engine temperatures is reached faster,
and the impact of these difficulties is minimized. Measurement of gaseous pollutants during engine warm-up is currently possible
with detectors used in standard exhaust gas analyzers (EGA), which have response times well-suited for sampling at such transient
conditions. However, these devices are not suitable for the measurement of exhaust emissions produced during extremely short
time intervals, such as engine starting. Herein, we present a methodology for the measurement of the cumulative pollutant
emissions during the starting phase of passenger car DI Diesel engines, with the goal of overcoming this limitation by taking
advantage of standard detectors. In the proposed method, a warm canister is filled with an exhaust gas sample at constant
volumetric flow, during a time period that depends on the engine starting time; the gas concentration in the canister is later
evaluated with a standard EGA. When compared with direct pollutant measurements performed with a state-of-art EGA, the proposed
procedure was found to be more sensitive to combustion changes and provided more reliable data. 相似文献
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《JSAE Review》1996,17(3):267-272
Combustion characteristics of a gasoline direct-injection (DI) engine were studied with fuel injection timing varied. This study showed that emissions at part load are reduced by optimizing in-cylinder air motion and injection timing. Antiknock quality and volumetric efficiency are improved at high loads. With our DI system fuel does not stick on the intake port wall during engine warmup and transient mode, and thus even a cold engine can be controlled with a quick response and a high resolution, which, as a result, can reduce emissions. Also, lean limit is significantly improved by optimizing the injection timing. 相似文献
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《JSAE Review》2002,23(3):297-302
In recent DI diesel engines designed to achieve high output and meet future exhaust regulation, the pilot injection control using a common-rail injection system is adopted. In this research, we developed visualization equipment for pilot combustion behavior of non-luminous flame to clarify the influence of pilot injection parameters (timing and quantity) on engine performance. As a result of this analysis, we clarified the influence of pilot injection parameters on pilot-main combustion and found the optimum pilot injection controlling method. 相似文献
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F. Payri A. J. Torregrosa A. Broatch L. Monelletta 《International Journal of Automotive Technology》2009,10(6):761-769
Combustion noise in passenger cars powered with direct injection (DI) diesel engines is frequently the main reason why end-users
are reluctant to drive this type of vehicle. Thus, the great potential of diesel engines for environment preservation — due
to their lower CO2 emissions — could be missed. This situation worsens with the current design trends (engine downsizing) and the emerging new
diesel combustion concepts (Homogeneous Charge Compression Ignition-HCCI, Premixed Charge Compression Ignition-PCCI, etc.),
which are intrinsically noisy. This negative feature can be even more critical in transient operation due to the contribution
of the temporal changes of both source and transmission path on engine noise. Therefore, combustion noise must be considered
as an additional essential factor in engine development, together with performance, emissions and driveability. Thus, suitable
evaluation procedures that can be integrated into the global engine development process in a timely and cost-effective manner
are imperative. Regarding the evaluation procedures, most of the work available in the literature addressed combustion noise
at steady operation. To surpass this limitation, two possible approaches — adapted from the classical and multiple regression
methods — for the overall level assessment of combustion noise in transient conditions are evaluated in this paper. 相似文献