Reducing cold-start emission from internal combustion engines by means of a catalytic converter embedded in a phase-change material

Under normal operating conditions, catalytic converters appear to be the mo st effective means of reducing air pollution from internal combustion (IC) engines. The conversion efficiency, however, declines very steeply for temp eratures below about 350 degrees C and is practically zero during the start ing and warming-up period. Improving the conversion efficiency under these conditions is important, particularly in large cities, where the number of startings per vehicle per day tends to be high. Among the more successful s olutions are preheating of the catalyst electrically, warming up of the cat alyst in an external combustion chamber, installation of an auxiliary small -capacity catalytic converter, and employment of an adsorbing unit between two catalysts. Although these methods are quite effective, their disadvanta ge lies in the fact that they require an external energy source, an additio nal component (a control unit) or a three-stage catalyst. In the present wo rk an investigation was made of a solution based on the exploitation of the rmal capacitance to keep the catalyst temperature high during off-operation periods. A phase-change material (PCM) with a transition temperature of 35 2.7 degrees C, which;is slightly above the light-off temperature of the met allic catalyst, was specially formulated, and a system comprising a catalyt ic converter embedded in the PCM was designed and tested. Under normal engi ne operating conditions, some of the thermal energy of the exhaust gases wa s stored in the PCM. During the time that the vehicle was not in use, the P CM underwent partial solidification, and the latent heat thus produced was exploited to maintain the catalyst temperature within the desired temperatu re range for maximum conversion efficiency.