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Technical Paper

Effects of DTBP on the HCCI Combustion Characteristics of SI Primary Reference Fuels

One option for ignition control of Homogeneous Charge Compression Ignition (HCCI) engines is to use small amounts of ignition-enhancing additives to alter the ignition properties. Di-tertiary Butyl Peroxide (DTBP) is one such additive and it has been suggested as a cetane improver in diesel engines. In this study, the effects of DTBP on spark ignition (SI) primary reference fuels (PRFs, n-heptane and iso-octane) and their blends (PRF20, PRF50, PRF63, PRF87 and PRF92) were investigated during HCCI engine operation. Experiments were run in a single cylinder CFR research engine for three inlet temperatures (410, 450 and 500 K) and several equivalence ratios (0.28 - 0.57) at a constant speed of 800 rpm and a compression ratio of 16.0. Experimental results show that ignition delay time, cycle to cycle variation, and stable operating range were all improved with the addition of less than 2.5% DTBP by volume.
Technical Paper

A Detailed Kinetic Study on the Effect of DTBP on PRF Combustion in HCCI Engines

The effect of Di-tertiary Butyl Peroxide (DTBP) on Primary Reference Fuels (PRFs) in Homogeneous Charge Compression Ignition (HCCI) engines was investigated numerically and was compared with trends from previous experimental observations. A detailed kinetic mechanism for PRF combustion containing more than a thousand species and four thousand reactions was combined with a twenty one species, sixty-nine reaction mechanism for DTBP decomposition. This mechanism predicted the observed experimental trends reasonably well and was used to examine how DTBP addition acts to advance combustion timing and to induce hot ignition for lean and high octane number mixtures. The study suggests that DTBP's predominant mode of action for low Octane Number (ON) fuels is thermal, while for high ON fuels it is chemical. The extended kinetic model compiled for this study and the results obtained can be used to aid in the understanding and development of tailored additives for HCCI engines.
Technical Paper

Time Resolved Exhaust Port Sampling Studies Related to Hydrocarbon Emissions from SI Engines

The role of post-combustion oxidation in influencing exhaust hydrocarbon emissions from spark ignition engines has been identified as one of the major uncertainties in hydrocarbon emissions research [l]*. While we know that post-combustion oxidation plays a significant role, the factors that control the oxidation are not well known. In order to address some of these issues a research program has been initiated at Drexel University. In preliminary studies, seven gaseous fuels: methane, ethane,ethene,propane,propene, n-butane, 1-butene and their blends were used to examine the effect of fuel structure on exhaust emissions. The results of the studies presented in an earlier paper [2] showed that the effect of fuel structure is manifested through its effect on the post-combustion environment and the associated oxidation process. A combination of factors like temperatures, fuel diffusion and reaction rates were used to examine and explain the exhaust hydrocarbon emission levels.
Technical Paper

Tracer Fuel Injection Studies on Exhaust Port Hydrocarbon Oxidation

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

Two Types of Autoignition and Their Engine Applications

The generally accepted explanation of autoignition in engines is that the reactivity is driven by temperature, where autoignition occurs after the mixture has reached some critical temperature (approx. 1000 K) by a combination of self-heating due to preignition reactions and compression heating due to piston motion and flame propagation. During the course of our investigations into autoignition processes and homogeneous charge compression ignition we have observed some ignitions that begin at much lower temperature (< 550 K). In this paper we describe these observations, our attempts to investigate their origins, and an alternative explanation that proposes that traditional models may be missing the chemistry that explains this behavior. Finally, applications of lower temperature chemical reactions are discussed.
Technical Paper

A Global Reaction Model for the HCCI Combustion Process

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.
Technical Paper

Some Observations on the Effects of EGR, Oxygen Concentration, and Engine Speed on the Homogeneous Charge Combustion of n-Heptane

NOx and soot emissions remain critical issues in diesel engines. One method to address these problems is to achieve homogeneous combustion at lower peak temperatures - the goal of research on controlled autoignition. In this paper n-heptane is used to represent a large hydrocarbon fuel and some of the effects of internal and external EGR, oxygen concentration, and engine speed on its combustion have been examined through simulation and experiment. Simulations were conducted using our existing skeletal chemical kinetic model, which combines the chemistry of the low, intermediate, and high temperature regimes. Experiments were carried out in a single cylinder, four-stroke, air cooled engine and a single cylinder, two stroke, water cooled engine. In the four-stroke engine experiments the effects of EGR were examined using heated N2 addition as a surrogate for external EGR and engine modifications to increase internal EGR.
Technical Paper

A Skeletal Chemical Kinetic Model for the HCCI Combustion Process

In Homogeneous Charge Compression Ignition (HCCI) engines, fuel oxidation chemistry determines the auto-ignition timing, the heat release, the reaction intermediates, and the ultimate products of combustion. Therefore a model that correctly simulates fuel oxidation at these conditions would be a useful design tool. Detailed models of hydrocarbon fuel oxidation, consisting of hundreds of chemical species and thousands of reactions, when coupled with engine transport process models, require tremendous computational resources. A way to lessen the burden is to use a “skeletal” reaction model, containing only tens of species and reactions. This paper reports an initial effort to extend our skeletal chemical kinetic model of pre-ignition through the entire HCCI combustion process. The model was developed from our existing preignition model, which has 29 reactions and 20 active species, to yield a new model with 69 reactions and 45 active species.
Technical Paper

Tracer Fuel Injection Studies on Exhaust Port Hydrocarbon Oxidation: Part II

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.
Technical Paper

Instrument for Field Monitoring of Carboxylate Coolants and Heat-Exchange Fluids

For several years now, organic acid based coolants and heat exchange fluids have been introduced on the automotive and industrial market place. The organic acid based coolants provide improved high temperature aluminum corrosion protection and longer drain intervals when compared to traditional coolants. In order to evaluate the organic acid based coolant quality in the field; the end user needs to be able to check several physico-chemical parameters of the coolant. First of all the amount of carboxylate based inhibitors should be determined because the customers can top the system with water. As a result the carboxylates can drop under the minimum required inhibitor level.
Technical Paper

Extended Life Carboxylate Coolant Compatibility with Other Coolant Technologies - Examining the Data

Previous studies examined the effect of low levels of silicate (∼<75ppm Si) on hot aluminum corrosion protection. The corrosion protection provided by different coolant technologies was evaluated at different silicate levels. The results indicated that small amounts of silicate have a negative effect on the corrosion protection of aluminum. This work will examine these results and evaluate the effectiveness of different laboratory tests for determining coolant “compatibility.” Results will be examined from several bench and fleet tests showing the effect of coolant mixing on the corrosion rates in various environments. The bench test results will include laboratory glassware and dynamic tests that have been used historically to evaluate coolant compatibility. Differences between the test methods will also be evaluated to determine the relevance of each test procedure in light of the fleet observations.
Technical Paper

Prediction of Pre-ignition Reactivity and Ignition Delay for HCCI Using a Reduced Chemical Kinetic Model

Homogeneous Charge Compression Ignition (HCCI) engines have the possibility of low NOx and particulate emissions and high fuel efficiencies. In HCCI the oxidation chemistry determines the auto-ignition timing, the heat release rate, the reaction intermediates, and the ultimate products of combustion. This paper reports an initial effort to apply our reduced chemical kinetic model to HCCI processes. The model was developed to study the pre-ignition characteristics (pre-ignition heat release and start of ignition) of primary reference fuels (PRF) and includes 29 reactions and 20 active species. The only modifications to the model were to make the proscribed adjustments to the fuel specific rate constants, and to enhance the H2O2 decomposition rate to agree with published data.
Technical Paper

The Autoignition of n-Pentane in a Non-Fired Single Cylinder Engine

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.
Technical Paper

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

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

Predictions of Cyclic Variability in an SI Engine and Comparisons with Experimental Data

An investigation of cyclic variability in a spark ignition engine is reported. Specifically, the predictions of an engine code have been compared with experimental data obtained using a well-characterized SI engine. The engine used for the experimental work and modeled in the code is the single cylinder research engine developed at Sandia National Laboratories and now operating at Drexel University. The data used for comparison were cylinder pressure histories for 110 engine cycles gathered during operation at a single engine operating condition. The code allows the various factors that could influence cyclic variability to be examined independently. Specifically, a model has been used to independently examine the effects of variations in equivalence ratio and of the turbulence intensity on cycle-to-cycle variations in the peak cylinder pressure, the crankangle of occurrence of peak pressure, the flame development angle, and the rapid burning angle.
Technical Paper

Coolant Pump Failure Rates as a Function of Coolant Type and Formulation

Automobile coolant pump failure rates have been observed to be influenced by the coolant inhibitor package. A fleet test consisting of 196 1991 Ford Crown Victoria taxi cabs was utilized to test six coolant formulations. Four of the test formulations were monobasic/dibasic organic acid technology coolants and two were traditional technology coolants containing nitrate, phosphate, and silicate. Coolant pump failure rates were monitored as a function of mileage. Results indicate that the service life of coolant pumps for those systems employing organic acid technology coolants was significantly greater than those systems utilizing traditional inhibitor technology coolants.
Technical Paper

A Compatibility Study of Mixtures of a Monoacid/Dibasic Acid Coolant and a Traditional Nitrite-Free Coolant

Mixtures of a novel corrosion inhibitor, based on the synergistic combination of aliphatic mono- and dibasic acids with a traditional coolant have been evaluated in: a stability test an electrochemical test the ASTM D 1384 Glassware Corrosion Test the ASTM D 4340 Aluminum Heat-Rejection Test a Dynamic Heat-Transfer Test. This paper discusses the results of these tests and the relevance of the tests in assessing the performance of the coolant mixtures. Recommendations are made to the selection of methods that provide significant information on coolant compatibility.
Technical Paper

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

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

Performance of Organic Acid Based Coolants in Heavy Duty Applications

Coolant formulations based on organic acid corrosion inhibitor technology have been tested in over 180 heavy duty engines for a total of more than 50 million kilometers. This testing has been used to document long life coolant performance in various engine types from four major engine manufacturers. Inspections of engines using organic acid based coolant (with no supplemental coolant additive) for up to 610,000 kilometers showed excellent protection of metal engine components. Improved protection was observed against cylinder liner, water pump, and aluminum spacer deck corrosion. In addition, data accumulated from this testing were used to develop depletion rate curves for long life coolant corrosion inhibitors, including tolyltriazole and nitrite. Nitrite was observed to deplete less rapidly in long life coolants than in conventional formulations.
Technical Paper

A Reduced Chemical Kinetic Model for Autoignition of the Butanes

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.