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The results of a comprehensive test program using a 1969 383-CID V-8 engine at two compression ratios-9.5:1 and 7.6:1-are reported. Compression ratio changes were effected by piston changes only. Except for necessary ignition timing modifications, no other changes were made in the engine. The effects of compression ratio changes on exhaust emissions and fuel consumption were studied in steady-state dynamometer tests and in vehicle tests. At MBT ignition timing or at the same percentage power loss from MBT timing at each compression ratio and with identical carburetion, decreasing the compression ratio from 9.5:1 to 7.6:1 produced the following results: 1. In steady-state dynamometer tests, NO (ppm) and CO (%) emissions were unchanged, HCs (ppm) were decreased, and fuel consumption was increased when equal power was developed at both compression ratios. 2. In vehicle tests using the 7-mode Federal Test Procedure, NO and CO emissions were unchanged and HCs increased somewhat.

The use of lead-free gasoline in conventional passenger car engines poses some problems that are discussed in this paper. Under heavy-duty operation, severe exhaust valve seat wear may occur. This will eventually result in one or more valves remaining open with extremely high exhaust emissions. The combustion chamber deposits formed in the absence of lead are typically more carbonaceous. These deposits have a higher heat capacity than lead deposits and the result, after extended mileage, is higher octane number requirements for the engines operated on nonleaded gasoline. The use of aromatic blending stocks to increase the octane number of nonleaded fuels to approach the octane quality of today's leaded gasolines increases undesirable exhaust emissions. The amounts of phenol, benzaldehyde, and total aromatic aldehydes in the exhaust gas are directly proportional to the aromaticity of the fuel.

Single-cylinder engine studies show that severity of the test cycle used for deposit accumulation markedly affects the level of exhaust emissions obtained with stabilized combustion chamber deposits. These studies also show that the relative stabilized emission levels with nonleaded and leaded fuels vary significantly with the aromatic content of the base fuel. An extensive evaluation in three groups of passenger cars operated by their owners in normal service showed no significant difference between the stabilized emission levels obtained with commercial nonleaded and leaded fuels. A dynamometer engine test procedure has been developed that simulates short-trip, city-type operation. The accelerated cooldown procedure allows for rapid accumulation of test mileage. Using this dynamometer procedure, the stabilized deposit emission levels of a commercial leaded fuel and a prototype nonleaded fuel are compared.

The development of a successful fuel additive requires considerable effort, a large share of which must be expended on the effect of the additive on engine durability. Durability may be affected as soon as the fuel enters the fuel tank and the possibility of such good or bad effects continues until the exhaust gases have cleared the rear bumper. Some of the durability aspects which can be either improved or made more severe are listed, these include fuel system corrosion, carburetor and manifold deposits, combustion chamber and spark plug deposits, engine wear and general cleanliness and bearing, exhaust system and rear bumper corrosion. It is shown that of seven experimental additives tested in a fleet of passenger cars of one make operated under severe duty conditions, four additives decreased exhaust valve life while three increased exhaust valve life by from twenty-five to fifty per cent.

Additives are essential ingredients of today’s motor gasolines. They enhance fuel quality by supplementing its natural characteristics or by providing new properties. As a result of additive use and modern refining methods, today’s inexpensive motor gasolines give excellent service performance and long storage life. This has permitted engine and equipment manufacturers to build more powerful and efficient equipment which operates with a minimum of service difficulties. In spite of the broad well-established use of additives by the petroleum industry, the average mechanical engineer engaged in engine or equipment development has little opportunity to become more than casually acquainted with them. Thus, he is unlikely to have more than a hazy idea of their functions. Nor is he likely to fully appreciate the extensive and thorough chemical and engineering development that usually precedes their marketing.

Data presented were obtained in an EMD 2-567 dual fuel engine when operated with leaded and unleaded LP gas. This study shows that, at the standard dual fuel engine compression ratio, knock limited power using a high propane content LP gas containing 3.18 gr/gal varied from 79–93% of full load diesel power, depending on engine speed. When the compression ratio was reduced from 13.6:1 to 11.9:1, full load diesel power was exceeded by 7–23%, depending on engine speed when using the same leaded LP gas.

RUMBLE is a type of abnormal combustion which may impose a limit on usable compression ratios if proper attention is not paid to fuel and lubricant factors. It is characterized by a low-frequency noise. This noise is much more likely to be present in engines which have been operated on light-duty schedules than in those which have been used in heavy-duty operation. Once deposits are present, rumble generally occurs at wide-open throttle and high engine speeds. Rumble does not appear to be confined to any particular type of combustion chamber, and increasing engine rigidity does not show promise of reducing the problem. Fuels with low deposit-forming tendencies help alleviate the problem. While not a complete cure, phosphorus fuel additives do a good job in reducing the incidence of rumble. This paper presents the results of work aimed at defining the problem, together with data illustrating the influence of various fuel factors.

A direct comparison of the effects [illegible] systems on fuel and and engine behavior has been made using the same V-8 engine far both systems. Fuel was metered by a standard four-barrel carburetor in one case, and by a timed manifold-port injection system in the other case. With both systems, provisions were made for varying fuel-air ratio. A major portion of the work was done on an engine dynamometer, with sufficient vehicle testing using the same engine and fuel metering systems to verify the laboratory results. When only the method of metering fuel was changed, the following results were obtained: 1. Brake horsepower increased slightly when fuel injection was used; the increase varied from zero to a little less than 3 % depending on engine speed. 2. Fuel economy, as measured by brake specific fuel consumption, was the same with both systems throughout the manifold vacuum load and speed range of the engine when each system was operated to provide minimum specific consumption. 3.

Major engine-design features of the 17.6 cu in. engine are described and engine development is traced by photographs and sectional drawings. Fuel testing with the 17.6 engine produced these results: ratings were obtained of many API-NACA pure hydrocarbons, which permitted relating variable compression-ratio results with supercharged results; Army-Navy performance numbers above 100 were established; the most sensitive fuels were indicated to be most prone to failure by preignition. The engine also contributed greatly to the development of spark plugs. The catalytic effects of spark plug electrode materials on the ignition of methyl alcohol and unleaded benzene are discussed.