Combustion and emissions of low heat rejection ceramic methanol ATAC engines

When methanol is used as fuel for internal combustion engines, formaldehyde and unburned methanol emissions can be a problem. To overcome this shortcoming, an engine with the active thermo-atmosphere combustion (ATAC) system was proposed, along with improvements in heat-insulating performance and the realization of high-temperature combustion by using ceramics for the combustion chamber walls. The combustion and emissions characteristics of this ceramic low heat rejection (LHR) methanol ATAC engine were investigated. Combustion performance was compared between operation with methanol and gasoline. When methanol was used, it was seen that the ATAC operation region was widened considerably. Also, a reduction in aldehyde emissions was achieved, due to the high-temperature operation of the combustion chamber. However, efficiency deteriorated at times due to early selfignition timing. This was overcome by the use of lean fuel-air ratios, which resulted in both a reduction of NO_x and an improvement in fuel consumption. With a premixed fuel supply system, wall surface ignition was unavoidable for combustion chamber surface temperatures greater than 800 K (527°C). Wall surface temperature swing and instantaneous heat flux increased substantially with ATAC operation under these conditions.