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Ethanol fuel has received renewed attention in recent years because of its oxygenate content and its potential to reduce greenhouse gas emissions from spark ignition engines. The economic impact on farm industry has been one of the drivers for its use in engines in the U.S. Although ethanol, in various blends, has been used in automotive engines for almost a decade the fuel has seldom been utilized in off-highway engines where the fuel systems are not well controlled. This investigation was conducted to evaluate exhaust emissions and combustion characteristics of E85 fuel in an off-highway engine used in farm equipment. A single-cylinder, four-stroke, spark ignition engine equipped with a carburetor was used to investigate combustion and exhaust emissions produced by gasoline and blends of gasoline and ethanol fuels. The engine fuel system was modified to handle flow rates required by the engine. A variable size-metering orifice was used to control air-to-fuel ratios.

Operation of spark ignition engine under lean mixture condition is one of the several options that may be used to meet pollution and fuel economy standards. In such an operation various factors influence the combustion phenomonon. To examine these, a study is conducted in a static chamber using lean propane air mixtures of different stoichiometry. Effects of ignition energy, electrode geometry, location of ignition source and temperature profile in the initial reaction zone are investigated. It was found that increasing ignition energy accelerated flame up to a certain point; any futher increase in energy had little effect on the flame acceleration. The rate of pressure rise also showed similar pattern. Temperature in the reaction zone was lower when the ignition point was near the wall than away from it; the temperature profile was mapped using laser interferometer techniques. Round tipped electrodes showed better repeatability and yielded lower ignition energy than the flat tipped.

An experimental study was conducted to determine potential of natural gas in lowering exhaust emissions from small spark ignition engines. A single cylinder, four-stroke, air-cooled spark ignition engine was used in the study. The investigation showed that increasing engine compression ratio from 8:1 to 10:1 reduced penalty in power normally associated with natural gas engine. The engine was able to run very stable at equivalence ratio as lean as 0.65 while the same engine could not be run at equivalence ratio below 0.85 on gasoline. Best thermal efficiency and reduced emissions of hydrocarbons and oxides of nitrogen were realized around equivalence ratio 0.75. Reducing equivalence ratio further lowered emissions of oxides of nitrogen significantly while increase in hydrocarbons was small. Most of the hydrocarbons in exhaust were of the methane type which have low ozone forming reactivity.

The wider flammability limit of lean natural gas-air mixtures offers potential for operating spark ignition engines on lean air-to-fuel ratios. However, at very lean equivalence ratios, the development of the initial flame and its subsequent propagation becomes highly sensitive to physical and chemical state of the mixture. This in turn, can adversely affect engine performance, particularly the cyclic variation in the combustion process. This paper discusses the effects of lean-burn operation on the flame development durations and the cycle-by-cycle variations in a natural gas fuel injected engine. The study was conducted on a 8-cylinder, 4.6 liter, spark-ignited engine. A data acquisition system is used to acquire 300 consecutive in-cylinder pressure cycles. A heat release model was used to estimate the initial flame development time and the rapid burn duration.

Small, gasoline fueled spark ignition engines are generally designed to operate at air to fuel ratios richer than stoichiometric. Consequently, they tend to emit high levels of carbon monoxide and hydrocarbons in their exhaust. This paper deals with an investigation of reducing emissions of carbon monoxide and unburned hydrocarbons by utilizing a small, metal matrix catalyst in conjunction with a thermal reactor. The experimental work was carried out on a small, single cylinder, air cooled, four stroke, spark ignition engine. The work was divided into two phases: Phase I was aimed at determining the extent to which oxidation of carbon monoxide and unburned hydrocarbons could be achieved using a two-way catalyst in conjunction with a thermal reactor. The work was later expanded to include a three-way catalyst in lieu of a two-way catalyst. In this phase controlled amounts of air from laboratory supply was used to achieve emission control.

An experimental study was undertaken to investigate burn characteristics of homogeneous charge natural gas fueled, single cylinder, spark ignition engine. The engine was instrumented with flame detection sensors, pressure transducer, a wide-range exhaust oxygen sensor and several other devices to measure parameters associated with charge and combustion. The pressure data was used in a model to estimate mass of charge burned during the combustion events. Engine compression ratio was varied within a small range. The flame kernel development time was influenced by mixture stoichiometry, engine load and speed. Very lean equivalence ratio had pronounced effect on kernel development. The combination of light load and very lean air-to-fuel ratio provided less favorable environment for the formation of stable flame kernel. An increase in compression ratio helped to shorten flame development time.

Gasoline-ethanol blends are being used or have been considered as a fuel for spark ignition engines. The motivation for using the blends varies in indifferent parts of the world and even in regions within a country. The increasing cost of gasoline, combined with regional tax incentives, is one of the reasons for increased interests in gasoline-ethanol blends in recent years in the U.S. Many vehicular engines are not designed to use a specific gasoline-ethanol blend. Rather, the engines have multi-blend capability, ranging from E0 to about E85. It is plausible that engine-out emissions will vary depending on the blend being used which may be further impacted by the level of EGR used with the blends. The present work was carried out to investigate engine out emissions when a vehicular spark-ignition engine was operated on E0 and E85 and different levels of EGR. A 4-cylinder, 2.5 liter, PFI engine was used in the experimental investigation.

A study was conducted to investigate combustion variability and exhaust emissions from high-speed, natural gas fueled engines. Two types of fuel systems were used in the investigation: a mixer and a port fuel injection. The overall engine performances were not much different at stoichiometric fuel-air ratio. But as the equivalence ratio was reduced the engine with the mixer produced higher levels of hydrocarbons and larger coefficient of variations in imep. The same engine exhibited longer flame development angle and rapid burn duration in comparison to the fuel injected engine. The differences in burn durations increased as the equivalence ratio decreased and the mixer system produced larger variations in their values at these operating points. The investigation showed the performance of the engine was better with natural gas injection system than with the mixer, particularly at lean equivalence ratios.

An experimental study was undertaken to investigate emissions of hydrocarbons, oxides of nitrogen, carbon monoxide, and methane hydrocarbons emitted by natural gas fueled engines and the extent of their conversion in catalysts. Two engines were used in the study: a four cylinder, 1.6 liter, spark ignition engine and a modified version of the same engine with only one of the cylinders operating at 0.4 liter capacity. Two-way and three-way catalysts were used to treat exhaust gases leaving the engine. Natural gas was supplied through gas carburetors operated at regulated pressures and supplying air-fuel ratios in the desired range. The results of the investigation showed that oxides of nitrogen could not be reduced in a three-way catalyst to the levels found in gasoline fueled engines when the operating air-fuel ratio was stoichiometric.

Natural gas is one of the alternative fuels that has received considerable attention in recent years. It is believed that spark ignition engines designed to operate on natural gas may be able to meet emissions regulations of the ULEV. Natural gas has some interesting characteristics which engine designers may be able to use successfully to meet impending regulations. However, concerns have been raised on the type of suitable catalyst for such engines and whether existing catalysts designed for gasoline fuel would meet natural gas engine requirements. The work described in this paper was conducted to assess suitability of some of the existing catalysts in lowering natural gas engine emissions.