It is well known that during engine cold-start, methanol fueled vehicles have a tendency to emit significant amount of unburnt methanol and formaldehyde, which is an oxidant of methanol The emission behavior and reduction methods of these components are studied in this paper
The reduction rate of these unburnt components exceeds 99% when the temperature of a catalyst is enough high However during engine cold-start the oxidative reaction can not begin, and it takes several minutes to warm up the catalyst After the temperature of the catalyst reaches to the light-off temperature it rises steeply and high reduction rates of these components are obtained at the same time Therefore, the catalyst temperature must be raised quickly and effectively in order to realize the proper oxidative reduction of unburnt methanol and formaldehyde emissions during engine cold-start
Consequently the effectiveness of installing pre-catalysts was examined in this study Some pre-catalysts (200cm3/piece) were placed after the exhaust manifold Results showed that within 10 minutes of initiating the idling experiment after engine cold-start the pre-catalysts were very effective and decreased emissions of the unburnt components by two thirds Moreover pre-catalysts which were electrically pre-heated with an external heater could more drastically decrease the amount of these components under the same experimental conditions
However for such electrical heating to be practical it is necessary to reduce the level of heating energy to as low an amount as possible Therefore two power-saving methods were tried One method consisted of installing a glow plug in the upper stream of the pre-catalyst This method was based on an idea that unburnt components coming in contact with the glow plug are activated and easily oxidized and that they then release thermal energy for quick heating The results showed that this method was effective for reduction (more than 40%) of unburnt methanol but was ineffective for reducing formaldehyde since spot heating caused a balancing of formaldehyde formation/decomposition Therefore another method was examined A small-sized electric heated pre-catalyst(50cm3)was installed in order to heat a full section of the exhaust stream of the catalyst The results showed that this method had a great effect in reducing these harmful substances Moreover, it was demonstrated that this method consumes little energy and is more practical as a means of heating