Exhaust and fuel characteristics during the warm-up phase of engine operation is in great need of improvement, especially for carburetted engines. Due to the number of short trips made by vehicles, a large proportion of urban driving occurs during warm-up operation.
The paper presents possibilities for achieving these improvements through modification of engine components (e.g., exhaust recirculation, oil and intake manifold heating). Tests were conducted on an Audi 80 LS. Through use of the described changes, fuel consumption beyond normal, hot-operation figures was reduced from 25% to only a few percent of the latter. Reductions of CO and HC emissions were 80% and 50%, respectively, although the erratic engine performance which is often characteristic of warm-up operation was somewhat aggravated. However, the results indicated that the problems associated with engine warm-up can be solved at acceptable costs. Further possibilities for improvements remain to be studied.