The Vapipe is a device that has been developed jointly by Shell Research Limited, Thornton Research Centre, and the National Engineering Laboratory to reduce car exhaust emissions and improve fuel economy. It achieves better mixing of the charge entering the engine by vaporizing the gasoline in the inlet system. Heat for this purpose is conveyed from the exhaust system by means of a heat pipe.The heat pipe must be designed to cater for the possibility of gross mismatch between the heat available from the engine exhaust and the heat needed to vaporize the fuel. This can occur under transient conditions of engine operation. Two Vapipe systems have been tested, one in which surplus heat from the exhaust is rejected to the cooling system of the car and the second in which the boiler efficiency is varied to maintain the correct flow of heat to the fuel vaporizer. Both systems operate well but the latter is very much cheaper to make than the former.Prototype Vapipes have been constructed and tested on test-bed engines, in cars on the road and on chassis dynamometers.The Vapipe provides good mixture distribution and allows the engine to run smoothly at weak mixtures, thus permitting improvements in fuel economy and reductions in exhaust emissions. Substantial benefits have been obtained in practical installations, but these could be even greater if carburetters or other fuel-metering devices were developed to take maximum advantage of the homogeneous mixtures. Significant improvements in engine warm-up time, driveability, and flexibility of operation are also achieved but power output is somewhat reduced.Progress has been made towards simplifying the design of the Vapipe and making the unit more compact.