Effect of air preheating on automotive emissions

Spark ignition engines in today's automobiles and trucks are a major source of urban air pollution. The engine exhaust is the source of NO, NO₂, and CO emissions. The exhaust, fuel tank and carburetor are the sources of unburned hydrocarbons. Almost 20% of the total distance travelled by automobiles consist of short trips from the starting point. In most cases, engine and driveline temperature will remain well below optimum levels in this period. Therefore in these cases, cold starting effects will influence the vehicle for a large proportion of driving time. The problem is enhanced in seasons of cold weather and high ambient humidity. Preheating the engine prior to cold starting has been reported as a good way to avoid many of these undesired effects. In the present study, CO emissions, rpm and water, oil, air and exhaust gases temperatures were determined in experiments of cold starting with and without preheating intake air of the engine. Results showed an important decrease in CO emissions and a good general performance of the engine when intake air was preheated.