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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

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

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

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.
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

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

Autoignition Chemistry Studies on Primary Reference Fuels in a Motored Engine

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

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

Corrosion Mechanism of High Lead Solder and Correlation to Dissolved Oxygen

High lead solder coupons are frequently tested in ASTM D 1384-87 and D 2570-91 tests to determine the corrosion protection provided by engine coolants. In contrast to 70/30 solder, high lead solder is often observed to show relatively high corrosion rates in D 1384-87 testing. Surprisingly, the high lead solder corrosion rates tend to be lower in the D 2570-91 test, despite the longer duration of this test. The basis of this effect has been investigated in different coolant formulations and in both ethylene glycol and propylene glycol. The corrosion of high lead solder was found to be directly related to the presence of oxygen in the D 1384-87 test. Replacement of the air purge with a nitrogen purge significantly reduced the corrosion rate of high lead solder in inhibited coolants. These results are interpreted in terms of the solder composition.
Technical Paper

Development of a Reduced Chemical Kinetic Model for Prediction of Preignition Reactivity and Autoignition of Primary Reference Fuels

A reduced chemical kinetic model has been developed for the prediction of major oxidation behavior of primary reference fuels (PRF's) in a motored engine, including ignition delay, preignition heat release, fuel consumption, CO formation and production of other species classes. This model consists of 29 reactions with 20 active species and was tuned to be applicable for the neat PRF's, 87 PRF and 63 PRF, and at various engine conditions. At the motored engine condition where detailed species data were generated, the model reproduces the ignition delay and the preignition heat release quite well (to within 15%). Fuel consumption and CO formation predictions differed from experiments by at most 25% for all of the four fuels. Predictions for other species classes generally agreed with experiments. As inlet temperature was varied, the experimentally observed negative temperature coefficient (NTC) behavior of iso-octane and 87 PRF was reproduced by the model.
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

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

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

Long Life Performance of Carboxylic Acid Based Coolants

An inhibitor package which is silicate-, nitrate-, borate- and phosphate-free has been developed as the basis for a world-wide automotive coolant formulation. The formulation contains aliphatic mono- and dicarboxylic acids and tolyltriazole as the sole inhibitors. Formulations containing carboxylic acid inhibitors have been studied in ASTM bench tests and found to sufficiently protect all prevalent cooling system metals. In addition, fleet tests have shown that carboxylic acid inhibitors deplete much more slowly than conventional inhibitors, making possible a much longer life coolant. Results from laboratory tests which simulate extended usage indicated that carboxylic acid-containing coolants have a significantly longer life span for the protection of all cooling system metals. Finally, the carboxylic acid/tolyltriazole inhibitor package is completely adaptable to a propylene glycol base.
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

Post Combustion Hydrocarbon Oxidation and Exhaust Emissions - Neat Fuel and Fuel Blend Studies

Inevitably a fraction of the hydrocarbon fuel in spark ignition engines escapes in-cylinder combustion and flows out with the burned products. Post combustion oxidation in the cylinder and exhaust port may consume a part of this fuel and plays an important role in determining exhaust emission levels. This paper presents results from experiments designed to identify the factors that control post-combustion oxidation. Regulated exhaust components and detailed hydrocarbon species were measured using seven neat hydrocarbons and four blends as fuel. The fuels were selected to compare the relative rates of mixing and chemical kinetics. The results indicate that exhaust temperature, diffusion rates and fuel kinetics each play a complicated role in determining emission levels.
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

Prediction of Preignition Reactivity for n-Butane and iso-Butane Blends Using a Reduced Chemical Kinetic Model

Recently, we reported the development of a new reduced chemical kinetic model for predicting reactivity and autoignition behavior of primary reference fuels in a motored research engine. The predicted oxidation behavior (ignition delay, preignition heat release, and evolution of key chemical species) is in fairly good agreement with experiments. In addition, the model reproduced the experimentally observed dependence of overall reactivity on charge density and manifold inlet conditions. This paper reports our initial effort to apply this new reduced chemical kinetic model to other fuels. Specifically, the model was tested using neat n-butane and n-butane/iso-butane blends (10, 20, and 48 percent by volume iso-butane) under skip fired conditions. The only adjustments made in the model were to the fuel specific rate parameters of the RO2· isomerization reaction, the reaction of aldehydes with OH·, and the reaction forming cyclic ethers.
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

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.