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THIS PAPER is a continuation of one presented at the 1928 Semi-Annual Meeting and gives the results of tests made to determine the effect of the A.S.T.M. 50-per cent point on acceleration and on the most economical fuel-volatility from the standpoint of acceleration. Test made in connection with the first investigation were on three special fuels and covered a range of manifold temperatures representing the extremes of winter warming-up and summer-operating temperatures. These tests showed a consistent variation in the relative accelerations as the manifold temperature was varied and that the effect on engine acceleration of increasing the A.S.T.M. 50-per cent point volatility is negligbile under most conditions except those under which a car is operated in the summer. In the second series of tests the objective was the quantity of each of the four special fuels that would give the same acceleration as United States Motor gasoline at an air-fuel ratio of 11.5 to 1.

INCIDENTAL to the cooperative fuel-research work of the author, which has been described in another paper, was a study of the effects of other operating factors. The results of these observations are presented in this paper. The effect of unequal fuel-distribution through the inlet manifold was studied by running acceleration tests on two cylinders at a time. Other series of acceleration tests showed the effect of jacket-water temperature with a cold inlet-manifold and of spark advance. Data are presented also from laboratory acceleration-tests simulating low-gear conditions, and showing that deceleration tests recorded by means of a spark accelerometer are useful in measuring friction under temperature conditions that are more nearly like the running conditions than are friction tests made by motoring the engine by means of a dynamometer.

SELECTION of a method and development of apparatus enabling precise and detailed measurement of engine acceleration is discussed in the first portion of this paper, the latter portion of which is concerned with the experimental results thereby obtained. Previous work on the influence of engine conditions on acceleration is generally substantiated. A method is described for approximately deriving the effective air-fuel ratio delivered to the cylinders during acceleration, practical applications are suggested, and limitations are discussed. The effect of fuel volatility on engine acceleration was studied, using six fuels: Aviation gasoline; commercial gasoline; a blend composed of equal parts of the two; and three especially prepared fuels, all of which have equal 20 and 90-per cent points but differ widely at the 50-per cent point. It is shown that the relative values of these fuels for acceleration depend upon the amount of vaporization in the manifold.