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Today's diesel PM reduction systems are mainly based on catalyzed particulate filter(CPF) systems. However, most of their reaction kinetics remain unresolved. Among others, the soot oxidation rate over catalyst is particularly important in the evaluation of the performance of the catalysts and the efficient control of CPF regeneration. This study, therefore, investigated the oxidation rate of carbon black (Printex-U) over various Pt supported catalysts using a flow reactor setup simulating diesel exhaust conditions. Compared to non-catalyzed soot oxidation, the oxidation rate of carbon black over Pt catalysts was to an extent shifted towards low temperatures. This activity enhancement of soot oxidation over a catalyst can be attributed principally to NO to NO2 conversion because NO2 oxidizes soot with much lower activation energy (Ea=60kJ/mol) than O2 (Ea=177kJ/mol).

This paper describes two types of computer models which have been developed to analyze the performance of both premixed-charge and direct-injection stratified-charge Wankel engines. The models are based on a thermodynamic analysis of the contents of the engine's chambers. In the first type of model, the rate of combustion is predicted from measured chamber pressure by use of a heat release analysis. The analysis includes heat transfer to the chamber walls, work transfer to the rotor, enthalpy loss due to flows into crevices and due to leakage flows into adjacent chambers, and enthalpy gain due to fuel injection. The second type of computer model may be used to predict the chamber pressure during a complete engine cycle. From the predicted chamber pressure, the overall engine performance parameters are calculated. The rate of fuel burning as an algebraic function of crank angle is specified.

A computer simulation of the turbocharged turbocompounded direct-injection diesel engine system has been developed in order to study the performance characteristics of the total system as major design parameters and materials are varied. Quasi-steady flow models of the compressor, turbines, manifolds, intercooler, and ducting are coupled with a multi-cylinder reciprocator diesel model where each cylinder undergoes the same thermodynamic cycle. Appropriate thermal loading models relate the heat flow through critical system components to material properties and design details. This paper describes the basic system models and their calibration and validation against available experimental engine test data. The use of the model is illustrated by predicting the performance gains and the component design trade-offs associated with a partially insulated engine achieving a 40 percent reduction in heat loss over a baseline cooled engine.

In this study, a set of performance and emissions data, obtained from a single-cylinder divided-chamber automotive diesel engine over the normal engine operating range, is described and analyzed. The data are used to evaluate a computer simulation of the engine's operating cycle, described in a companion paper, which predicts the properties of gases inside the engine cylinder throughout the cycle, and engine efficiency, power and NOx emissions. Satisfactory agreement between predictions and measurements is obtained over most of the engine's operating range. The characteristics of the experimental pre- and main-chamber pressure versus crank angle data are then examined in detail. A heat release analysis appropriate for divided-chamber diesel engines is developed and used to obtain heat release rate profiles through the combustion process.

An experimental study was performed to develop a more fundamental understanding of the effects of secondary air injection (SAI) on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of engine operating parameters and various secondary air injection strategies such as spark retardation, fuel enrichment, secondary air injection location and air flow rate were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Time-resolved HC, CO and CO₂ concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to time-resolved mass emissions by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.

The high concentration of particulate matter (PM) in diesel exhaust gas causes significant soot deposition on the wall of EGR cooler, and reduces the heat transfer performance of the EGR cooler and the reduction rate of NOx. The deposition of PM tends to be occurred more severely with "heavy wet PM," which is more frequently at the LTC (low temperature combustion) engine. The objective of this work is to evaluate the effects of soluble organic fraction (SOF) on deposit characteristics of the EGR cooler. To measure reliable mean particle concentration values and surrogate SOFs, the soot generator with SOF vaporizer was used. As for two surrogate SOFs, n-dodecane and diesel lube oil, deposit mass increased when they were injected. Especially from the experiment results, it was found that the lube oil effect was more significant than the n-dodecane effect and lube oil also had a stronger effect on reduction of thermal conductivity by filling pores in deposits.

A single-zone burn-rate analysis based on measured cylinder pressure data proposed by Gatowski et al. in 1984 was evaluated over the full load and speed range of a spark-ignition engine. The analysis, which determines the fuel mass burning rate based on the First Law of Thermodynamics, includes sub-models for the effects of residual fraction, heat transfer, and crevices. Each of these sub-models was assessed and calibrated. Cylinder pressure data over the full engine operating range obtained from two different engines were used to examine the robustness of the analysis. The sensitivity of predictions to the parameters wall temperature, heat transfer model coefficients and exponent, swirl ratio, motoring polytropic constant, in-cylinder mass, and to uncertainty in pressure data was evaluated.

Characteristics of soot oxidation were investigated with a carbon black (Printex-U). A flow reactor system which can simulate the condition of diesel particulate filter and diesel exhaust gas (1 bar, O2 0 ∼ 10%, NO2 200 ∼ 900ppm) was designed and used with the temperature programmed oxidation (TPO) and constant temperature oxidation (CTO) techniques. The temperature increase rate was 5°C/min for TPO experiments. From the experiments, the apparent activation energy for carbon oxidation with nitrogen dioxide was determined as 60 ± 3 kJ/mol with the first order of carbon in the range of 10∼90% oxidation and the temperature range of 250∼500°C. This value was exceedingly lower than the activation energy of oxygen oxidation which was 177 ± 1 kJ/mol. When oxygen exists with nitrogen dioxide, the reaction rate increased with the concentration of oxygen. Its rate of increase was faster for low oxygen concentration and slower for high concentration.

Plasma-catalyst (Ag, Au/Al2O3) systems were applied to NOx reduction in a model lean-burn engine exhaust gas. Also, DeNOx test of real diesel exhaust gas was performed by plasma-Ag/Al2O3 system. In the case of model exhaust gas, the catalytic activity for NOx reduction was enhanced by the assistance of plasma in the wide temperature range. The NOx conversion efficiency of plasma-Ag/Al2O3 was 40∼90% under the condition of C3 H6 3200ppm (C1/NOx = 5.96) and 10% O2 over the temperature range of 250∼400°C. The plasma-Au/Al2 O3 system showed remarkable low temperature NOx reduction activity at 100∼250°C. The real engine full flow test was performed for 70% of the full load and at engine speed of 1500rpm. NOx removal of 46% from the diesel exhaust gas was achieved by the plasma-Ag/Al2O3 catalyst system at 364°C(C1/NOx = 6). In the case of higher C1/NOx = 10, the NOx conversion increased up to 73% at 381°C. Also, DeNOx engine tests were performed for full load of 1500, 2000 and 2500rpm.

The oxidation of soot (carbon black) which is assisted by Pt/CeO2 catalyst is studied using a flow reactor system simulating the condition of diesel exhaust. In this study, the temperature programmed oxidation (TPO) scheme is mainly used for different NO and O2 concentrations and soot oxidation rate is evaluated by monitoring both CO and CO2 concentrations. Pt/CeO2 catalyst lowers the temperature of the peak CO/CO2 concentrations significantly when there is either NO or O2. Oxidation starts at 200°C and the peak CO2 concentration is observed at 360°C, which depends on the amount of catalyst and NO concentration. The effect of catalyst on NO2 recycling is also investigated. For this purpose, two different types of sample have been prepared. For the mixed case, 10mg of carbon black is mixed with 50mg of Pt/CeO2 catalyst under conditions of loose contact. For the unmixed case, the catalyst layer is placed on top of soot layer without mixing.

A model for predicting the performance and emissions characteristics of Wankel engines has been developed and tested. Each chamber is treated as an open thermodynamic system and the effects of turbulent flame propagation, quench layer formation, gas motion, heat transfer and seal leakage are included. The experimental tests were carried out on a Toyo Kogyo 12B engine under both motoring and firing conditions and values for the effective seal leakage area and turbulent heat transfer coefficient were deduced. The agreement between the predicted and measured performances was reasonable. Parametric studies of the effects of reductions in seal leakage and heat transfer were carried out and the results are presented.

A computational fluid dynamics (CFD) prediction of the transient flow in the intake system of a spark ignition engine is compared to experimental data. The calculation was performed for a single cylinder version of a pre-1995 Ford two-valve production engine, while experiments were carried out on a single cylinder Ricardo Mark 3 research engine with similar overall geometric parameters. While the two engines have somewhat different geometries, this was not considered to be a significant problem for our study of flow features. Both set-ups employed gaseous fuel. The calculation was performed using the commercially available Star-CD code incorporating the complete intake manifold runner and cylinder into the mesh. Cylinder pressures were in good agreement with experiment indicating that wave dynamics were well captured. Comparison was also made to the measured instantaneous gas temperatures along the intake system.

In analyzing the processes inside the cylinder of an internal combustion engine, the principal diagnostic at the experimenter's disposal is a measured time history of the cylinder pressure. This paper develops, tests, and applies a heat release analysis procedure that maintains simplicity while including the effects of heat transfer, crevice flows and fuel injection. The heat release model uses a one zone description of the cylinder contents with thermodynamic properties represented by a linear approximation for γ(T). Applications of the analysis to a single-cylinder spark-ignition engine, a special square cross-section visualization spark-ignition engine, and a direct-injection stratified charge engine are presented.

Time-resolved heat flux and gas temperature measurements in the intake port of a spark ignition engine are presented. Experiments were pursued for motored, propane fired, and liquid fuel operation. Heat transfer coefficients were built from the dry data. Also, heat transfer rates in the port and off the back of the intake valve were integrated over the main flow phases. For a typical low-load propane-fired operating condition, heat transfer in the port caused a mean intake air temperature increase of approximately 10°C. The main different intake flow phases, induction or forward flow, displacement backflow, and valve overlap backflow, contributed approximately 10°C, 3°C, and negative 3°C, respectively. These mixture temperature changes are expected to be also applicable for liquid fuel injected cases. While the heat flux instrumentation was primarily intended for dry operation of the engine, liquid fuel experiments were also pursued.

A conventional spark plug and a spark plug with smaller electrodes were studied in M.I.T.'s transparent square piston engine. The purpose was to learn more about how the electrode geometry affects the heat losses to the electrodes and the electrical performance of the ignition system, and how this affects the flame development process in an engine. A schlieren system which provides two orthogonal views of the developing flame was used to define the initial flame growth process, for as many as 100 consecutive cycles. Voltage and current waveforms were recorded to characterize the spark discharge, and cylinder pressure data were used to characterize the engine performance. The spark plug with the smaller electrodes was shown to reduce the heat losses to the electrodes, and thereby extend the stable operating regime of the engine. At conditions close to the stable operating limit, cycle-by-cycle variations in heat losses cause significant cyclic variations in flame development.

The flow and heat transfer phenomena in the intake port of a spark ignition engine with port fuel injection play a significant role in the mixture preparation process, especially at part load. The backflow of the hot burned gas from the cylinder into the intake port when the intake valve is opened breaks up any liquid film around the inlet valve, influences gas and wall temperatures, and has a major effect on the fuel vaporization process. The backflow of in-cylinder mixture with its residual component during the compression stroke prior to inlet valve closing fills part of the port with gas at higher than fresh mixture temperature. To quantify these phenomena, time-resolved measurements of the hydrocarbon concentration profile along the center-line of the intake port were made with a fast-response flame ionization detector, and of the gas temperature with a fine wire resistance thermometer, in a single-cylinder engine running with premixed propane/air mixture.

In order to understand better the operation of spark-ignition engines during the warm-up period, a computer model had been developed which simulates the thermal processes of the engine. This model is based on lumped thermal capacitance methods for the major engine components, as well as the exhaust system. Coolant and oil flows, and their respective heat transfer rates are modeled, as well as friction heat generation relations. Piston-liner heat transfer is calculated based on a thermal resistance method, which includes the effects of piston and ring material and design, oil film thickness, and piston-liner crevice. Piston/liner crevice changes are calculated based on thermal expansion rates and are used in conjunction with a crevice-region unburned hydrocarbon model to predict the contribution to emissions from this source.

The fate of hydrocarbon species in the exhaust systems of spark-ignition engines is an important part of the overall hydrocarbon emissions problem. In this investigation models were developed for the instantaneous heat transfer, fluid mixing, and hydrocarbon oxidation in an engine exhaust port. Experimental measurements were obtained for the instantaneous cylinder pressure and instantaneous gas temperature at the exhaust port exit for a range of engine operating conditions. These measurements were used to validate the heat transfer model and to provide data on the instantaneous cylinder gas state for a series of illustrative exhaust port hydrocarbon oxidation computations as a function of engine operating and design variables. During much of the exhaust process, the exhaust port heat transfer was dominated by large-scale fluid motion generated by the jet-like flow at the exhaust valve.

NOx reduction by a plasma/catalyst system was tested with modeled gas and real exhaust gas. Ag/Al2O3 was used as the catalyst. The oxidation of NO to NO2 by the plasma was increased as HC concentration and input energy density increase. The presence of H2O in the reactant gas led to the production of acid by plasma. The catalytic activity for NOx reduction was enhanced by the assistance of plasma especially in the lower temperature region. This activity was a little suppressed in the presence of H2O, but the acid was not detected in the effluent gas treated by the plasma/catalyst system. The NOx conversion to N2 was evaluated by a gas chromatography in the model gas with helium as the balance gas. The result in helium balance gas showed the selectivity to N2 depended on the catalyst temperature and was also enhanced by the assistance of plasma. The 50% of NOx removal from the diesel exhaust gas was achieved by the plasma /catalyst system.

The prediction of knock onset in spark-ignition engines requires a chemical model for the autoignition of the hydrocarbon fuel-air mixture, and a description of the unburned end-gas thermal state. Previous studies have shown that a reduced chemistry model developed by Keck et al. adequately predicts the initiation of autoignition. However, the combined effects of heat transfer and compression on the state of the end gas have not been thoroughly investigated. The importance of end-gas heat transfer was studied with the objective of improving the ability of our knock model to predict knock onset over a wide range of engine conditions. This was achieved through changing the thermal environment of the end gas by either varying the inlet air temperature or the coolant temperature. Results show that there is significant heating of the in-cylinder charge during intake and a substantial part of the compression process.