Abstract
II. THE have already explained how important in the economical development of the internal-combustion engine is an accurate and precise knowledge of the physical properties of the working medium. The two chief features of which a knowledge is required are the calorific value of the explosive mixture and the relation between the specific heat and temperature of the ignited gases. The Calorific value has been carefully ascertained for most of the gases commonly used, but the specific-heat relation is still a matter of unfortunate uncertainty. At the Leicester meeting of the British Association in 1907, under the sectional presidency of Prof. Silvanus P. Thompson, the desirability of clearing up the doubts that surrounded this subject was so keenly felt that an important committee was appointed for “the investigation of gaseous explosions, with special reference to temperature.” An account of the findings of this committee was published in NATURE of June 24 last. From our present point of view the important result of the committee's work is expressed in the following extract from its report:—“Recent researches on the properties of the gases at high temperatures have definitely shown that the assumption of constant specific heat is erroneous, and have given sufficient information about the magnitude of the error to show that it is of material importance… The closer approximation to the real cycle which is made by taking account of the actual properties of the working fluid, though it leads to some complication of formulæ, gives compensating advantages of real practical value.” This bears out, also, a remark made by the late Prof. Zeuner2 to the effect that “at any rate there must be dropped from the theory of the internal-combustion motors the former assumption of the constancy of the specific heats of the products of combustion.” A curve connecting the specific heat at constant volume (Cv) of the mixture of gases, formed by the explosion of one part of coal gas in nine parts of air, with temperature centigrade (θ), which was considered to be accurate within 5 per cent., was included in the committee's report. A formula which fits this curve closely is Cv=0.172+0.075θ/1000 and although the constant in the second term on the right-hand side of this equation can only be looked upon as a first estimate, however carefully chosen, the equation does, probably, represent the high-water mark in our present-day knowledge, and from it can be deduced the limiting-theoretical efficiency of engine cycles in which such a working medium is employed.
Article PDF
References
"Technical Thermodynamics", by Prof. Zeuner .
Proc. I.C.E., vol. clxix., p. 145.
"The Steam Engine", by Prof. Perry, p. 117.
Rights and permissions
About this article
Cite this article
WIMPERIS, H. Recent Improvements in the Internal-Combustion Engine 1 . Nature 81, 201–203 (1909). https://doi.org/10.1038/081201a0
Issue Date:
DOI: https://doi.org/10.1038/081201a0