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Recently, studies were conducted on a single cylinder, four stroke engine to investigate the effect of temperature and local mixedness on exhaust port hydrocarbon oxidation. To examine the effect of temperature, hydrocarbon tracers (propane, propene, 1-butene, n-butane, and n-pentane) were individually injected into the exhaust port just behind the exhaust valve for operating conditions that provided different exhaust port temperatures. For the local mixedness experiments, tracer mixtures (propane + n-butane, 1-butene + n-butane, propene + n-butane) were injected into the exhaust port just behind either a normal exhaust valve or a shrouded exhaust valve. The concentration of tracers and their reaction products were measured using gas chromatography of samples withdrawn from the exhaust stream. The tracer consumption behavior with changing port temperature confirmed that there is a minimum port temperature for hydrocarbon oxidation.

Autoignition chemistry of n-heptane, iso-octane and an 87 octane blend, 87 PRF, was studied in a single-cylinder modified Wisconsin model AENL engine under motored conditions. Use of a fast-acting sampling valve and gas chromatographic analysis allowed measurement of in-cylinder gas composition during the ignition process. Crank angle resolved species evolution profiles were generated for all three fuels at a fixed inlet temperature of 376 K. For n-heptane, the measurements were made during a cyclically repeatable two stage ignition process up to the point of hot ignition (the second stage ignition). These n-heptane experiments were run at ø = 0.3 to avoid excessive pressure rise at hot ignition which might damage our engine. iso-Octane and 87 PRF were run at stoichiometric equivalence ratio which did not have a second stage ignition, and species were measured only during the first stage of ignition.

This paper presents results of studies investigating the effect of octane enhancing ethers on the reactivity of an 87 octane mixture of primary reference fuels, 87 PRF, in a motored engine. 87 PRF was blended with small percentages of MTBE, ETBE, TAME and DIPE based on a constant gravimetric oxygen percentage in the fuel. The experiments were conducted in a modified single-cylinder Wisconsin AENL engine at compression ratios of 5.2 and 8.2. Supercharging and heating of the intake charge were used to control reactivity. The inlet gas temperature was increased from 320 K, where no reactivity occurred, until either autoignition occurred or the maximum temperature of the facility was reached. Exhaust carbon monoxide levels and in-cylinder pressure histories were monitored in order to determine and quantify reactivity.

The detailed chemical reactions leading to autoignition of n-pentane are investigated in this study. A single-cylinder engine operating in a nonfired mode was used. The engine is supercharged and the temperature of the inlet fuel/air mixture is varied. By increasing the inlet manifold temperature, at a given inlet manifold pressure, the fuel/air mixture can be made to undergo autoignition. In-cylinder pressure and temperature profiles were measured. Gas samples from the combustion chamber were extracted and analyzed using gas chromatography techniques. The detailed chemical reaction mechanisms explaining the products from the different stages of the fuel oxidation process are presented. It is speculated that the generation of OH radicals from the peroxide (QOOH) decomposition is responsible for the autoignition of the n-pentane fuel/air mixture.