Aldehydes and Methanol Emission Mechanisms and Characteristics from a Methanol/Gasoline-Fueled Spark-Ignition (SI) Engine

Formaldehyde (HCHO), acetaldehyde (CH 3 CHO), and methanol (CH 3 OH) emission characteristics as well as their conversion efficiencies on the three-way catalytic converter (TWC) were investigated on a three-cylinder, spark-ignition (SI) engine when it ran on gasoline and M85 (gasoline/methanol = 15:85), respectively. In addition, their emission mechanisms were simulated on a plug flow reactor (PFR) model with the detailed kinetic mechanism of primary reference fuels as well. Simulation results show that there exist contribution zones for both HCHO and CH 3 CHO emissions in pipes along with decrescent temperatures; it contains two subzones of the generation zone (Z G ) and the following generation−consumption zone (Z G−C ). Aldehydes emissions become the peak value at the critical point, and the critical temperature of HCHO is higher than that of CH 3 CHO. The increase of the initial temperature and residence time of the gases in the pipe will move the aldehydes emissions from Z G to Z G−C along the emission profiles. The initial temperature of the exhaust pipe lies between the critical temperatures of HCHO and CH 3 CHO; thus, the HCHO emission decreases while the CH 3 CHO emission increases with the increase of the engine torque, i.e., initial temperature. With the increase of the engine speed, the decrease of the residence time takes the dominant role, the HCHO emission increases, while the CH 3 CHO emission decreases. However, the initial temperature in TWC is higher than the critical temperature of CH 3 CHO; the aldehydes conversion efficiencies decrease; and minus efficiencies appear at high engine speeds. Simulation results coincide well with the emission characteristics.