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An investigation was conducted into pressure pulsation in the exhaust port, which greatly affects volumetric efficiency and engine performance. From experiments using a single blow-down generator, it was established that the amplitude of the pressure pulsation increases as the manifold branch is lengthened and that large negative pressure synchronized with the timing of valve overlap can be obtained if a proper branch length is used. The performance of a 2ℓ test engine was optimized by varying the length of both the manifold branches and front pipe forks. It was found that whereas front pipe fork length affects engine performance over only a narrow range of engine speed, optimizing manifold branch length results in a considerable improvement over a wide engine speed range. In the course of optimizing the exhaust pipe manifold length of this two-degree-of-freedom exhaust system, abnormal exhaust noises were emitted at specific engine speeds during deceleration.

In order to determine the main factors causing the mileage-related increase in formaldehyde emission from methanol-fueled vehicles, mileage was accumulated on three types of vehicle, each of which had a different air-fuel calibration system. From exhaust emission data obtained during and after the mileage accumulation, it was found that lean burn operation resulted in by far the highest formaldehyde emission increase. An investigation into the reason for the rise in engine-out formaldehyde emission revealed that deposits in the combustion chamber emanating from the lubricating oil promotes formaldehyde formation. Furthermore it was learnt that an increase in engine-out NOx emissions promotes partial oxidation of unburned methanol in the catalyst, leading to a significant increase in catalyst-out formaldehyde emission.

A statistical indicator data analyzer has been developed, which is able to analyze various combustion characteristics such as rate of pressure increase, heat release rate, etc., from indicator data of four hundred (400) combustion cycles of each cylinder of a multicylinder engine. Statistical analyses on cycle-by-cycle variation of indicated mean effective pressure (imep) were made under various combinations of fuel systems and combustion chamber configurations to clarify those effects. The contribution of characteristics on the variation of imep was made clear to some extent.

To elucidate the effects of EGR, the gas compositions in the cylinder at the end of the compression stroke, have been analyzed. The relationship of the burned gas fraction in the cylinder (defined as BGR) to NOx emission and misfire limit have been investigated and imply the following: 1) NOx and misfire limit are strongly affected by the BGR at specified air fuel ratio and spark timing. 2) Gas-fuel ratio which is the ratio of the total gas to the fuel in the cylinder is the predominant factor used extensively to evaluate the effects of EGR and/or lean mixture on NOx and misfire limit of an engine.

The new California regulations governing emission of oxides of nitrogen from automobile exhausts present a special problem to small engine manufacturers, for little of the available data enable them to satisfy the requirements and still produce vehicles that have maximum power output and maximum fuel economy. This report provides essential information for designers and alerts them to the danger of adverse effects on engine and vehicle performance resulting from the usual corrective measures of rich mixture, retarded spark timing, and exhaust gas recyling. Engine modifications and an effective gas recyling method are suggested in this report to alleviate these undesirable side effects.