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Technical Paper

Tracer Fuel Injection Studies on Exhaust Port Hydrocarbon Oxidation

1998-10-19
982559
Time resolved exhaust port sampling results show that the gas mixture in the port at exhaust valve closing contains high concentrations of hydrocarbons. These hydrocarbons are mixed with hot in-cylinder gases during blowdown and can react either via gas phase kinetics in the exhaust port/runner system or subsequently on the exhaust catalyst before they are emitted. Studies were conducted on a single cylinder, four stroke engine in our laboratory to determine the interaction between the hot blowdown gases and the hydrocarbons which remain in the exhaust port. A preselected concentration and volume of hydrocarbon tracers (propane, propene, n-butane, and 1-butene) in either oxygen/nitrogen mixtures or pure nitrogen were injected into the exhaust port just behind the exhaust valve to control the initial conditions for any potential oxidation in the port.
Technical Paper

The Effects of Methanol and Ethanol on the Oxidation of a Primary Reference Fuel Blend in a Motored Engine

1995-02-01
950682
This experimental study was conducted in a motored research engine to investigate the effect of blending methanol and ethanol on hydrocarbon oxidation and autoignition. An 87 octane mixture of primary reference fuels, 87 PRF, was blended with small percentages of the alcohols to yield a constant gravimetric oxygen percentage in the fuel. The stoichiometric fuel mixtures and neat methanol and ethanol were tested in a modified single-cylinder engine at a compression ratio of 8.2. Supercharging and heating of the intake charge were used to control reactivity. The inlet gas temperature was increased from 325 K to the point of autoignition or the maximum achievable temperature of 500 K. Exhaust carbon monoxide levels and in-cylinder pressure histories were monitored in order to determine and quantify reactivity.
Technical Paper

A Reduced Chemical Kinetic Model for Autoignition of the Butanes

1996-10-01
962106
A reduced chemical kinetic model by Li et al. [1]* for predicting primary reference fuels' reactivity and autoignition behavior was modified to apply to the butanes, and it was correlated to experimental results from the non-fired engine cycles under skip fired conditions. The fuels examined in this work were neat n-butane and n-butane/iso-butane blends (10, 20, and 48 percent by volume iso-butane). In our initial work using measured pressure data from the first skip cycle, we modified Li et al.'s model by only adjusting the fuel specific rate parameters of the alkylperoxy radical (RO2·) isomerization reaction, the reaction of aldehydes with OH·, and the reaction forming cyclic ethers. In this work, analysis was extended to the second skip cycle and additional oxidation rate parameters with high fuel sensitivity were adjusted. Several reactions, which are not significant in butane oxidation, were temporarily made to be inactive in the model.
Technical Paper

The Effects of Octane Enhancing Ethers on the Reactivity of a Primary Reference Fuel Blend in a Motored Engine

1994-03-01
940478
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.
Technical Paper

Autoignition Chemistry Studies on Primary Reference Fuels in a Motored Engine

1994-10-01
942062
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.
Technical Paper

A Study on the Application of a Reduced Chemical Reaction Model to Motored Engines for Heat Release Prediction

1992-10-01
922328
We investigated the ability of a reduced chemical kinetic model of 18 reactions and 13 active species to predict the heat release for a blend of primary reference fuels with octane rating 63 in a motored research engine. Given the initial fuel-air mixture concentration and temperature, the chemical kinetic model is used to predict temperature, heat release and species concentrations as a function of time or crank angle by integrating the coupled rate and energy equations. For comparison, we independently calculated heat release from measured pressure data using a standard thermodynamic model.
Technical Paper

Fuel and Diluent Effects on Diesel Odor Species in a Premixed Flat Flame

1986-02-01
860221
As a group of diesel engine exhaust products, oxygenated hydrocarbons have been found to be responsible for the characteristic diesel odor. Contadictory effects of fuel properties on the emission levels of these species in both diesel engines and spray burner experiments have been reported. In the present study, a prevaporized premixed flat flame was used to investigate the fuel and diluent effects on these species. The results suggest a definite fuel effect on formation rates of oxygenates. In general, aromatic fuels produced higher concentration levels of oxygenates than paraffins, and the oxygenate concentration increases as the carbon number increases for the straight chain compounds. GC/MS analysis of the oxygenate fraction of the samples indicated a similar oxidation mechanism for all alkanes. Branching of alkanes was found to lead to more cyclization, but not always higher oxygenate levels.
Technical Paper

A Global Reaction Model for the HCCI Combustion Process

2004-10-25
2004-01-2950
This paper presents a new global reaction model to simulate the Homogeneous Charge Compression Ignition (HCCI) combustion process. The model utilizes seven equations and seven active species. The model includes five reactions that represent degenerate chain branching in the low temperature region, including chain propagation, termination and branching reactions and the reaction of HOOH at the second stage ignition. Two reactions govern the high temperature oxidation, to allow formation and prediction of CO, CO2, and H2O. Thermodynamic parameters were introduced through the enthalpy of formation of each species. We were able to select the rate parameters of the global model to correctly predict the autoignition delay time at constant density for n-heptane and iso-octane, including the effect of equivalence ratio.
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