The Effects of Initial Conditions on the Composition of the On-Board Fuel Reformation Chamber in an HCCI Engine

2015 ◽  
Vol 733 ◽  
pp. 219-224
Author(s):  
Chun Hua Zhang ◽  
Le Xue

Based on the CHEMKIN software, a model of the reforming chamber was built to simulate the on-board fuel reforming process in a Homogeneous Charge Compression Ignition (HCCI) engine. The effects of the initial pressure and temperature of the chamber on the reformed gas were studied. The results show that the main species in the reformed gas are H2 and CO. This paper investigated the effect of initial temperature on the reformed gas, in order to get the optimum initial temperature. Under the optimum initial temperature (1300 K), some important conclusions have been drawn by changing initial pressures of the chamber. Initial pressure may have great effect on other species, but has a small effect on mole fractions of H2 and CO. By comparing the concentrations of H2 and CO between low and high initial pressures under the optimum initial temperature, it can be concluded that H2 and CO are still the main species in the reformed gas.

2008 ◽  
Vol 9 (5) ◽  
pp. 399-408 ◽  
Author(s):  
T Shudo

A homogeneous charge compression ignition (HCCI) engine system fuelled with dimethyl ether (DME) and methanol-reformed gas (MRG), both produced from methanol by onboard reformers using exhaust heat, has been proposed in previous research. Adjusting the proportions of DME and MRG with different ignition properties effectively controlled the ignition timing and load in HCCI combustion. The use of the single liquid fuel, methanol, also eliminates the inconvenience of carrying two fuels while maintaining the effective ignition control effect. Because reactions producing DME and MRG from methanol are endothermic, a part of the exhaust gas heat energy can be recovered during the fuel reforming. Methanol can be reformed into various compositions of hydrogen, carbon monoxide, and carbon dioxide. The present paper aims to establish the optimum MRG composition for the system in terms of ignition control and overall efficiency. The results show that an increased hydrogen fraction in MRG retards the onset of high-temperature oxidation and permits operation with higher equivalence ratios. However, the MRG composition affects the engine efficiency only a little, and the MRG produced by the thermal decomposition having the best waste-heat recovery capacity brings the highest overall thermal efficiency in the HCCI engine system fuelled with DME and MRG.


Author(s):  
Hu Tiegang ◽  
Liu Shenghua ◽  
Zhou Longbao ◽  
Zhu Chi

Dimethyl ether (DME) is a kind of fuel with high cetane number and low evaporating temperature, which is suitable for a homogeneous charge compression ignition (HCCI) engine. The combustion and emission characteristics of an HCCI engine fuelled with DME were investigated on a modified single-cylinder engine. The experimental results indicate that the HCCI engine combustion is a two-stage heat release process. The engine load or air-fuel ratio has significant effects on the maximum cylinder pressure and its position, the shape of the pressure rise rate and the heat release rate. The engine speed has little effect. A DME HCCI engine is smoke free, with zero NOx and low hydrocarbon and CO emissions under the operating conditions of 0.25–0.30 MPa brake mean effective pressure.


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