Numerical Study on Optimal Operating Conditions of Homogeneous Charge Compression Ignition Engines Fueled with Dimethyl Ether and n-Heptane

The auto-ignition and combustion mechanisms of dimethyl ether (DME) in a fourstroke homogeneous charge compression ignition (HCCI) engine were investigated using a zero-dimensional thermodynamic model coupled with a detailed chemical kinetics model. The results indicate that DME displays two-stage auto-ignition, and heat release with a low-temperature reaction and a high-temperature reaction (HTR). Heat release with the HTR can be separated into two stages: blue flame and hot flame. HCCI ignition is controlled by hydrogen peroxide (H2O2) decomposition, and OH plays a very important role in HCCI combustion. Formaldehyde (CH2O) is the main source of H2O2. Based on the sensitivity analysis of chemical reactions, the major paths of the DME reaction occurring in the engine cylinder are clarified. The major paths of the DME reaction is H-atom abstraction from DME, followed by the first addition of O2 and second addition of O2, and then oxidation to formaldehyde (CH2O), the formyl radical (HCO), and finally carbon monoxide (CO). CO oxidation occurs at the hot flame by the elementary reaction CO + OH = CO2 + H. At leaner DME concentrations, CO cannot be completely converted to carbon dioxide (CO2), and the process will result in high CO emissions.

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Numerical study of the combustion mechanism of a homogeneous charge compression ignition engine fuelled with dimethyl ether and methane, with a detailed kinetics model. Part 2: the reaction kinetics of dimethyl ether and methane dual-fuel

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/095440705x34829 ◽

2005 ◽

Vol 219 (10) ◽

pp. 1225-1236 ◽

Cited By ~ 3

Author(s):

M Yao ◽

J Qin ◽

Z Zheng

Keyword(s):

Heat Release ◽

Methane Oxidation ◽

Dimethyl Ether ◽

Homogeneous Charge Compression Ignition ◽

Numerical Study ◽

Kinetics Model ◽

Dual Fuel ◽

Compression Ignition ◽

Compression Ignition Engine ◽

Homogeneous Charge

A numerical study was carried out using a zero-dimensional detailed chemical kinetics model to investigate the chemical reaction phenomena encountered in the homogeneous charge compression ignition process of a dimethyl ether (DME) and methane dual-fuel mixture. The results show that the heat release of DME/methane dual-fuel combustion is a typical two-stage process: the first stage is mainly associated with DME oxidation, and the second is mainly the result of methane oxidation. The low-temperature reaction (LTR) of DME is inhibited, the second molecular oxygen addition of DME is restrained, and β-scission plays a dominant role in DME oxidation. Therefore, methane changes the paths of the LTR of DME. Most of the formaldehyde (CH2O) is produced from H abstraction of methoxy (CH3O) rather than from the LTR of the DME. The heat release by DME oxidation and the existence of H2O2 generated by DME oxidation make methane oxidation occur at a low initial temperature. However, methane oxidation also promotes hot flame reactions of DME. During the second stage of heat release, OH is produced in many different ways rather than only by way of H2O2 decomposing in neat DME oxidation; this results in higher OH mole fraction when dual fuel is used compared with DME alone. Finally, the major paths of the DME/methane HCCI reactions occurring in the engine cylinder are clarified.

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Experimental and Numerical Study on Auto-Ignition and Combustion of Homogeneous Charge Compression Ignition Fueled With Dimethyl Ether

ASME 2005 Internal Combustion Engine Division Spring Technical Conference ◽

10.1115/ices2005-1054 ◽

2005 ◽

Author(s):

Ma-Ji Luo ◽

Zhen Huang ◽

De-Gang Li

Keyword(s):

Diesel Engine ◽

Dimethyl Ether ◽

Homogeneous Charge Compression Ignition ◽

Numerical Study ◽

National Laboratory ◽

Zone Model ◽

Compression Ignition ◽

Hcci Combustion ◽

Key Species ◽

Homogeneous Charge

Experimental study of the autoignition and combustion characteristics of homogeneous charge compression ignition (HCCI) was carried out on a modified diesel engine fuelled with Dimethyl ether (DME) fuel. Numerical simulations were also performed by using the detailed chemical kinetic mechanism of DME oxidation proposed by American Lawrence Livermore National Laboratory (LLNL). The experimental results indicate that HCCI combustion with DME fuel can be realized in diesel engine with a few modifications, and it has a two-stage heat release characteristics. The emissions of HCCI combustion with DME fuel can be characterized by free of smoke and near zero NOx. The simulation results suggest that the single-zone model can accurately predict the ignition timings, including the low temperature ignition and high temperature ignition. The variations of key species (such as H2O2, CH2O, OH, HCO, CH, etc) with crank angle during fuel oxidation and the effects of engine operating parameters on HCCI combustion can also be analyzed by numerical simulation.

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