THIS REPORT covers tests made at the laboratory of several automobile companies to ascertain the effect of engine design and of different fuels on the acceleration characteristics of a number of different engines.
The work was authorized by the Cooperative Fuel Research Steering Committee as an extension of the program of fuel research because the tests on fuel volatility and engine acceleration made by the Bureau of Standards were all made on one engine.
The present report describes the types of manifold and manifold jacketing used on the six and eight-cylinder engines and the conditions under which tests were made with three fuels supplied by the Bureau. Results of uniform acceleration tests on seven engines are given and discussed. Two facts that are said to appear with reasonable consistency are that the curves of relative effectiveness of the three fuels for producing acceleration tend to cross at the lower temperatures and the blend of equal parts of Domestic Aviation gasoline and U. S. Motor gasoline produces roughly one-half more improvement in acceleration than does Aviation gasoline over U. S. Motor fuel.
Typical curves showing the effect on acceleration of updraft and downdraft manifolds, manifold shape, manifold heat and accelerating devices are presented and discussed. An empirical rule is given for finding the relative effectiveness of fuels for acceleration at any given manifold temperature.
Considering design factors, it is pointed out that, for both updraft and downdraft manifolds, the acceleration is in the order of the fuel volatilities up to 500 r.p.m., and from there up to 1,000 r.p.m. is in the reverse order, due to over-richness.
The increase in acceleration that results from accelerating charges and from supplying heat to the manifold is shown by curves and discussed. These show that the heat and accelerating charge improve the acceleration up to about 500 r.p.m. but that reversal occurs at higher speeds. The conclusion is drawn that, at factory setting of the carbureter for maximum power, the addition of heat, accelerating charges and increase in volatility of the fuel all serve to increase the acceleration at engine speeds below about 700 r.p.m. but to decrease the acceleration at higher speeds.