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RESULTS of an investigation directed toward determining why deposits increase antiknock requirement are discussed here. Data are presented which indicate that substantially 100% of the increase in octane-number requirement caused by deposits results from a combination of thermal and volume effects. An analysis procedure is given which indicates that deposit-thermal effects may result entirely from the heat that is stored in the deposits. Thus, the deposits absorb heat during the combustion process in one cycle and transfer it to the fresh charge during the intake and compression portions of the next cycle. The findings reported in this paper show that those engines with the smallest area of combustion-chamber surface, for a given displacement, would be expected to have the smallest thermal effects and hence should have minimum deposit effects.

AN improved method, applicable to either motored or fired engines, for evaluating energy release rate occurring during preflame reactions is described in this paper. A unique feature of this method is the use of a mechanical computer to handle calculations. A smooth energy-release-rate curve can be obtained with this improved analysis technique-something not possible with two previous methods. However, the mean rate of energy release as determined by all three methods is in general agreement.

DESIGN details for many of the passenger-car engines being built in Britain are presented here. Illustrations are used, wherever available, to make the details clear to the reader. The author points out that the well-known Royal Automobile Club formula is no longer used in determining the British vehicle tax. This formula was considered by many British designers a millstone around their necks. It is based on piston area, and so they were almost forced to design their engines with small bore and long stroke to keep down taxes on the car. Thus, the author reveals, the present tendency seems to be toward cylinder proportions approaching square and, in some cases, even over-square.

Previous procedures for estimating diluent in used railway diesel lubricating oils all have drawbacks. Precision is limited in simple procedures. A research procedure is time consuming and requires specialized equipment and highly skilled personnel. The authors describe a graphic correlation for estimation of amount and type of diluent as functions of decrease in flash and viscosity. Also included are empirical methods for development of the dilution chart without recourse to experimental blends of the oil with diluents.

High speed photographs of the combustion process in an engine equipped with a quartz window, in the cylinder head are described. The optical path was so arranged that direct and shadowgraph images of flames could be separately photographed on the same film at the same time in conjunction with flywheel timing marks. Simultaneous pressure-time records were also obtained. The photographs confirm the well-known fact that knock occurs immediately after the portion of fuel still unreached by the flame spreading from the spark plug spontaneously ignites and begins to burn very rapidly. Cylinder pressure then rises so fast that acoustic resonance develops in the combustion gases and is heard as knock. Four types of combustion phenomena in the engine were investigated: normal flames, “cool” flames, “hot” flames, and knock. With no spark ignition, cool flames start at the valve end of the L-head combustion chamber and end at the far side over the piston.

Twenty thousand hours of testing in six automotive diesels show how sulfur content, aromatics content, and average boiling point of the fuel affects deposits and wear. Sulfur tends to increase deposits and wear throughout these engines over a wide range of operating conditions. Higher aromatics contents and average boiling points increase deposits at specific points in the engines but have little effect on wear. However, the magnitude of these effects differs so much with engine design and type of operation that generalizations are unwise. The best fuel composition for any given situation can only be determined by studying the specific conditions to be met.

The results of LPG motor fuel service tests in city busses of the Wichita Transportation Company are given which indicate that the inclusion of appreciable percentages of propylene in LPG motor fuel had no detrimental effects on the operation of city bus engines. Comparison tests between test fuel containing 15 per cent propylene and the fleet LPG motor fuel were conducted in six city busses operated for approximately 25,000 miles each in regular city route service. Evaluation of results in terms of change in Knock-limited spark advance during the test period and visual inspection of combustion chamber deposits were the basis of the conclusion that LPG motor fuels containing 15 per cent propylene afforded wholly satisfactory performance in this city bus service.

An investigation has been carried out under conditions comparable to normal engine operation to ascertain the effects of an additive such as nitromethane on the power output, fuel consumption, and efficiencies which result therefrom. It has been learned that nitromethane can increase power output by as much as 13 percent on an indicated or gross basis when added to methyl alcohol and by 7 percent when added to a benzene-isooctane mixture in concentrations of 20% by volume. By so doing, the indicated specific fuel consumption increases, but contrary to expectations, so does the indicated thermal efficiency. The results from the benzene-isooctane blend were comparable to those from the methanol in all respects except for the increase in power, which was not as great. The amount of nitromethane which can be added to a given fuel is a function of its tendency to bring about preignition in the engine.

No profound or basic discoveries eliminating wear of the subject parts are reported in this paper, but data and observations on some speculative aspects are presented. The data offered is, in itself, largely inconclusive, but may enable others to view their data from new angles and may inspire some new approaches to solution of old problems. It is shown that wear rates are subject to wide and unexplained variation. An analysis of possible factors on this variation is made. Is wear increased by extremely low oil consumption? Some new data on this old question is offered. Finally, an analysis of characteristics of the new engines is made, indicating that we may be facing some new problems.