HCCI Combustion Characteristics of Hydrogen and Hydrogen-rich Natural Gas Reformate Supported by DME Supplement 2006-01-0628
Hydrogen is expected to be a clean and energy-efficient fuel for the next generation of power sources because it is CO2-free and has excellent combustion characteristics. In this study, an attempt was made to apply Homogeneous Charge Compression Ignition (HCCI) combustion to hydrogen with the aim of achieving low oxides of nitrogen (NOx) emissions and high fuel economy with the assistance of the di-methyl-ether (DME) fuel supplement. As a result, HCCI combustion of hydrogen mixed with 25 vol% DME achieved approximately a 30% improvement in fuel economy compared with HCCI of pure DME and spark-ignited lean-burn combustion of pure hydrogen under almost zero NOx emissions and low hydrocarbon (HC) emissions. This is attributed to control of the combustion process to attain the optimum onset of combustion and to a reduction of cooling losses.
This combustion concept was extended to hydrogen-rich Natural gas Reformed Gas (NRG), in a system in which both NGR and DME are expected to be produced from natural gas onboard, and the same improvement was achieved. It was found that raising the compression ratio from 13:1 to 15:1 was effective in reducing the ratio of DME required for HCCI with the same improvement in fuel economy combined with low NOx and HC emissions.