At least 200 hydrocarbon (HC) compounds have been identified in exhaust. Some such as the olefin compounds react products. These are termed reactive hydrocarbons. Others such as the paraffin are virtually unreactive.
Special Developments
The Stratified-Charge Engine a modification of the conventional spark-ignition piston engine, the stratified charge engine is designed to reduce emissions without the need for an exhaust-gas recirculation system or catalytic converter. Its key feature is a dual combustion chamber for each cylinder, with a prechamber that receives a rich fuel-air mixture while the main chamber is charged with a very lean mixture. The spark ignites the rich mixture that in turn ignites the lean main mixture. The resulting peak temperature is low enough to inhibit the formation of nitrogen oxides, and the mean temperature is sufficiently high to limit emissions of carbon monoxide and hydrocarbon.
Two rather distinct means for accomplishing the stratified charge condition are under consideration :
1. A single combustion chamber with a well-controlled rotating air motion. This arrangement is illustrated (Fig.6) by the Texaco Combustion Process (TCP), patented in 1949.
2. A prechamber or two-chamber system. This is illustrated by Fig.7, which shows the general arrangement of the Honda Compound-vortex controlled-combustion (CVCC) system.
For both systems, very careful development has proved to be necessary to obtain complete combustion of the fuel under the wide range of speed and load conditions required of an automotive engine.