The Effect of Exhaust-to-Coolant Heat Transfer on Warm-up Time and Fuel Consumption of Two Automobile Engines

A 1977 Buick V-6 engine and a 1981 Ford Granada automobile were equipped with heat exchangers to transfer energy from the exhaust gases to the cooling water after cold starts in order to shorten engine warm-up periods and improve fuel economy. A parallel concern was the time required to reach satisfactory heat delivery to the passenger compartment.

The Buick engine was investigated in the laboratory. The Ford automobile was tested during driving over a 12.4 km length of freeway and over an 8.6 km test route including both in-town and highway segments. Prior to each test run the engines were exposed to ambient air for at least 8 hours at temperatures ranging from −26° C to + 2° C.

The use of the heat exchangers resulted in average reductions of fuel consumption of 2.8% during a 7 minute warm-up period for the engine, and of 2.2% for the autombile when tested on the above test routes. The corresponding times for the coolant in the automobile compartment heater to reach maximum temperature were reduced by 16% and 7%. While fuel savings were achieved, their economic value is questionable, particularly in light of a possible retrofit of an existing automobile with an exhaust-to-coolant heat exchanger and the necessary control equipment.