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Lean combustion in spark-ignition engines has long been recognized as a means of both improving engine efficiency and lowering carbon monoxide and oxides of nitrogen exhaust emissions. In this paper, the fundamentals of lean combustion are reviewed in terms of lean flammability and ignition, and lean misfire limit, from a compilation of research results. 125 references are included in the review. The effect of lean mixture on engine efficiency, performance and exhaust emissions is discussed. The effects of engine variables on lean combustion are presented, including mixture preparation, ignition, combustion chamber shape, compression rates and fuel additives. Techniques for lean burn engine control and emissions clean-up are also described.

Automobile racing engine performance has historically progressed with and aided the development of automotive technology. Racing engine performance has been improved in various applications with specialized liquid fuels, such as nitroparaffins, alcohol (methanol) and certain hydrocarbons used in racing gasolines. This paper presents physical and thermodynamic properties of commonly used racing fuels and selected additives, including nitrous oxide and hydrazine. Improving the antiknock properties of gasoline for racing purposes is also discussed. Engine operating characteristics and power output for each fuel are discussed in terms of appropriate fuel properties and engine parameters such as air/fuel ratio and compression ratio. Combustion of various fuels is discussed along with the effect of dissociation and heat loss on performance. Some experimental performance data are presented, and theoretical and practical considerations which effect fuel utilization are also discussed.

Single-cylinder engine tests, with computerized data aquisition, of several nitroparaffin and methanol fuel blends were conducted to identify engine operating conditions or fuel compositions which reduced combustion knock with no penalty to engine power. The effect of variation in equivalence ratio, nitromethane percentage in selected co-solvents, ignition timing and compression ratio was investigated at fixed engine speed and steady-state temperatures. Electronic filters were used to isolate the portion of the cylinder pressure signal containing combustion knock and a Fast Fourier Transform computer subroutine was used to characterize combustion severity in the frequency domain. The results verified the empirical racing engine practice that for a nitromethane/methanol mixture operating fuel-rich from stoichiometric, power is increased and knock is decreased.

The aerodynamic drag of rolling vehicles was studied by towing pairs of side-by-side identical small-scale models in rolling contact with the bottom of a water-filled trough. An instrumented towbar measured the difference in the models' overall drag forces in order to determine the effect of changes in a model's configuration on its aerodynamic drag. The effects of wheel-rim covers, axle fairings, and wheel-housing volume on vehicle drag were studied with the test apparatus. The magnitude of the effects were well outside the range of experimental error, and correlated well with published results of similar studies performed in wind tunnels. Testing indicated that lift-induced changes in vehicle rolling resistance would not significantly alter results of tow testing under normal circumstances. Advantages of the underwater tow test include the ability to inexpensively simulate rotating wheels and to study the interaction between rotating wheels on a moving vehicle and the ground plane.