Natural gas HCCI engine operation with exhaust gas fuel reforming

Natural gas has a high auto-ignition temperature, requiring high compression ratios and/or intake charge heating to achieve homogenous charge compression ignition (HCCI) engine operation. It is shown here that hydrogen in the form of reformed gas helps in lowering the intake temperature required for stable HCCI operation. It has been shown that the addition of hydrogen advances the start of combustion in the cylinder. This is a result of the lowering of the minimum intake temperature required for auto-ignition to occur during the compression stroke, resulting in advanced combustion for the same intake temperatures. This paper documents experimental results using closed loop exhaust gas fuel reforming for production of hydrogen. When this reformed gas is introduced into the engine, a decrease in intake air temperature requirement is observed for a range of engine loads. Thus for a given intake temperature, lower engine loads can be achieved. This would translate to an extension of the HCCI lower load boundary for a given intake temperature.