New Emphasis on Fuel Volatility-Effects on Vehicle Warmup with Quick-Release Chokes

Quick-release chokes may become an essential feature of advanced exhaust emission control systems to minimize emissions during warmup. However, quick-release chokes greatly impair warmup driveability when gasolines of conventional volatility are used. Consequently, modifications of gasoline volatility were investigated as one approach to restoring warmup driveability with quick-release chokes.

Warmup driveability of two test cars equipped with quick-release chokes was measured on a chassis dynamometer at 40 and 68 F using fuels with widely different volatility characteristics. Warmup driveability was essentially restored by increasing fuel volatility in the 40-90% ASTM distillation range. Front-end volatility up to the 40% point had very little effect.