The Simulation Of On-Board Fuel Reformation And Experimental Research On An HCCI Engine

With the rapid development of automobile industry in China, as the main power source of the automobile, Internal Combustion Engine(ICE) also faces with the challenges of both energy-saving and environment-protection. Therefore, the new generation of combustion mode-Homogeneous Charge Compression Ignition(HCCI) has been put forward.HCCI is a new kind of combustion mode. The homogeneous intake charge enters into the cylinder and the autoignition happens only relying on the compression of piston. It breaks the trade-off limitation between NOx and Particulate Matter(PM) emissions in conventional diesel engines since it contains the fea0 tures of both conventional diesel and gasoline engines. There are so many researchers that has been attracted to focus on HCCI engine because of its extensive sources of fuel supply.The main work and results are as follows:1) Simulation and parameters optimization. A new on-board fuel reformation model fuelled with n-butanol in an HCCI engine was made by using CHEMKIN software and the mixture concentration in the reforming chamber was calculated. The optimized reforming parameters have been achieved at the specific operation condition. The way to achieve this goal is to establish a suitable reforming chamber over the cylinder head. The reforming chamber was used to produce reformed gas which would be used in the next cycle to mix with the mixture in the main cylinder so that in-cylinder combustion and reaction path would be affected.The results show that the parameters of the reorming system were optimized with reforming chamber mixture concentration of 0.4, reforming chamber volume of 4mL(with an effective εr of 15.8), traped phase of 20°CA and reforming phase of-5.2°CA under the conditions of the overall concentration of 3.0, engine speed of 1200r/min and intake temperature of 433 K. The results indicate that on-board fuel reformation method works properly in both controlling the combustion phase and extending the operation range.2) Experimental research. A CT2100 Q double-cylinder diesel engine has been modified to achieve HCCI combustion mode in one of the cylinder. HCCI combustion test was conducted first fuelled with n-butanol. The influences of intake temperature, mixture concentration and engine speed on combustion, emission characteristics and engine performance were investigated. Then, a direct injection system fuelled with n-heptane was set up based on the HCCI mode cylinder, which could be used to investigate the influence of direct injection on HCCI combustion. The comparison between with and without direct injection system was made in both combustion characteristics, emission characteristics and engine performance as well. The influences of direct injection pressure, the direct injection quantity, the direct injection phase and the intake temperature with direct injection system on combustion, emission characteristics and engine performance were studied. It has been shown that the peak in-cylinder pressure, peak in-cylinder temperature and peak heat release rate increased with the increase of intake temperature, and these peak values occurred earlier as well as the combustion phase. The other trend is the emissions of HC and CO decreased with the increase of intake temperature. The influence of mixture concentration on combustion parameters is obvious. When the mixture was becoming rich, the combustion parameters went up apparently, but the effects were complicated for the emissions of HC and CO. The Indicated Mean Effective Pressure(IMEP) and ηi were decreased as the mixture was going lean. Engine speed has a slight influence on HCCI combustion. In-cylinder pressure, pressure rise rate, heat release rate and in-cylinder temperature increased slightly with the increase of engine speed. The Coefficient Of cyclic Variation(COV) of the peak in-cylinder pressure was the smallest at the speed of 1200r/min.It can be seen that HCCI combustion fuelled with n-butanol was improved by using n-heptane direct injection. A smaller cyclic variation was detected and more stable running of HCCI engine was achieved. The combustion phase could be controlled to some extent and both of IMEP and ηi were improved, and the operation range of HCCI engine has also been extended. The direct injection pressure has a limited influence on HCCI engine, but there is optimized direct injection pressure(Pinject=6MPa) that has been matched with the combustion chamber shape to achieve a good quality of HCCI combustion. Peak in-cylinder pressure, peak pressure rise rate, peak heat release rate and peak in-cylinder temperature all increased and occurred in advance with the increase of total mixture concentration(namely, the direct injection quantity of n-heptane increased). There is an optimized total λt=1.15(with the n-heptane injection quantity of 13mg/cycle) that could make HCCI combustion the best. CA05 and CA50 occurred earlier and combustion duration were shortened. The direct injection phase has an obvious influence on combustion phase. When the direct injection event was delayed until after compression Top Dead Center(TDC), cyclic variation was increased quickly. Also, there is an optimized φin(φin=340°CA) that could make a good performance of HCCI engine.