A Study of Thermal Energy Conservation in Exhaust Pipes

The emissions of hydrocarbons (HC) and carbon monoxide (CO) from a vehicle can be decreased by obtaining faster warmup of the catalytic converter. An experimental study of the consequences of effectively internally insulating an exhaust pipe has demonstrated (1) a significant increase in converter-inlet gas temperature during warmup, and (2) a lowering of HC and CO emissions on the Federal Test Procedure by about 15% on one particular vehicle. A mathematical model has been developed and verified to predict converter-inlet temperature histories from known exhaust-takedown temperature histories and to quantify the effects of various insulation material properties on the temperature of the gas entering the converter. The dangers of drawing misleading conclusions from tests of exhaust pipe insulation are discussed.