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A two-dimensional finite element program has been developed to analyze the transient heat flow paths in low-heat-rejection engine combustion chambers. This analysis tool is used to study the transient heat transfer performance of a ceramic-coated piston with steel-alloy rings reciprocating within a ceramic-coated iiner at a speed of 1900 revolutions per minute. Throughout the cycle, the instantaneous boundaries of the combustion chamber are defined based on the position of the piston against the liner. Then, appropriate boundary conditions are applied to the component surfaces at every instant. Instantaneous piston and liner temperature distributions, heat transfer rates from the working fluid to these two components, as well as heat transfer rates between the two components are calculated by the program. The results are compared against the performance of a baseline cast-iron piston-liner assembly.

Contrary to the thick thermal barrier coating approach used in adiabatic diesel engines, the authors have investigated the merits of thin coatings. Transient heat transfer analysis indicates that the temperature swings experienced at combustion chamber surfaces depend primarily on material thermophysical properties, i.e., conductivity, density, and specific heat. Thus, cyclic temperature swings should be alike whether thick or thin (less than 0.25 mm) coatings are applied, Furthermore, thin coatings would lead to lower mean component temperatures and would be easier to apply than thick coatings. The thinly-coated engine concept offers several advantages including improved volumetric efficiency, lower cylinder liner wall temperatures, improved piston-liner tribological behavior, and improved erosion-corrosion resistance and thus greater component durability.

Finite element models of various fast-response thermocouple designs have been developed. Due to the small differences in thermal properties between thermoelements and metal engine components, standard co-axial thermocouples can measure transient temperatures of metal components within an accuracy of 98%. However, these relatively small errors in total temperature measurement translate into as high as 30% errors in indicated peak-to-peak-temperature swings for iron surfaces. The transient swing errors result in up to 30% errors in peak heat flux rates to iron surfaces. These peak heat flux errors can be substantially larger if coaxial thermocouples are used for heat flux measurements in aluminum or ceramic surfaces. Increasing the thin film thickness is a compromise solution to reduce the discrepancy in peak heat flux measured with coaxial designs in metal engines. An alternative overlapping thin film thermocouple design has also been evaluated.

An experimental investigation is being conducted to study the heat release and transient heat transfer characteristics of a single cylinder diesel engine. Pressure and transient temperature data from two stationary locations in the cylinder head were used to calculate heat release and transient heat flux rates for various injection timings, speeds, and loads. As injection timing is retarded, the heat release indicates a shift from predominantly pre-mixed combustion to largely diffusion limited combustion. Changes in load affected mainly the diffusion phase of combustion, while changes in speed more strongly affected the pre-mixed portion of combustion. Fluxes calculated at both locations reflect the prominent traits of the heat release profiles, but lag several crank angle in phase. The surface temperature and flux over the bowl were greater than over the crown. The flux at the outer location exhibited greater variation as engine operating conditions were changed.

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.

A computer simulation of the Homogenous Charge Compression Ignition (HCCI) four-stroke engine has been developed for combustion and performance studies. The simulation couples models for mass, species, and energy within a zero-dimensional framework. The combustion process is described via a user-defined chemical kinetic mechanism. The CHEMKIN libraries have been used to formulate a stiff chemical kinetic solver suitable for integration within a complete engine cycle simulation, featuring models of gas exchange, turbulence and wall heat transfer. For illustration, two chemical kinetics schemes describing hydrogen and natural gas chemistry have been implemented in the code. The hydrogen scheme is a reduced one, consisting of 11 species and 23 reactions. The natural gas chemistry is described via the GRI-mechanism 3.0 that considers 53 species and 325 reactions, including NOx chemistry.

Exhaust gas recirculation (EGR) coolers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases in order to reduce NOX emissions. Engine coolant is used to cool EGR coolers. The presence of a cold surface in the cooler causes fouling due to particulate soot deposition, condensation of hydrocarbon, water and acid. Fouling experience results in cooler effectiveness loss and pressure drop. In this study, possible soot deposition mechanisms are discussed and their orders of magnitude are compared. Also, probable removal mechanisms of soot particles are studied by calculating the forces acting on a single particle attached to the wall or deposited layer. Our analysis shows that thermophoresis in the dominant mechanism for soot deposition in EGR coolers and high surface temperature and high kinetic energy of soot particles at the gas-deposit interface can be the critical factor in particles removal.

EGR coolers are mainly used on diesel engines to reduce intake charge temperature and thus reduce emissions of NOx and PM. Soot and hydrocarbon deposition in the EGR cooler reduces heat transfer efficiency of the cooler and increases emissions and pressure drop across the cooler. They may also be acidic and corrosive. Fouling has been always treated as an approximate factor in heat exchanger designs and it has not been modeled in detail. The aim of this paper is to look into fouling formation in an EGR cooler of a diesel engine. A 1-D model is developed to predict and calculate EGR cooler fouling amount and distribution across a concentric tube heat exchanger with a constant wall temperature. The model is compared to an experiment that is designed for correlation of the model. Effectiveness, mass deposition, and pressure drop are the parameters that have been compared. The results of the model are in a good agreement with the experimental data.

Wall wetting of injected fuel onto the intake manifold and cylinder wall causes unpredictable transient behavior of air-fuel mixing which results in a significant emission of unburned hydrocarbon (HC) emission during cold start operation. Heated exhaust gas oxygen (HEGO) sensors cannot measure the air-fuel ratio (A/F) of exhaust gas during cold start condition. Precise and fast estimation of air/fuel ratio of the exhaust gas is required to elucidate the wall wetting phenomena and subsequent HC formation. Refined A/F estimation can enable the control of fuel injection minimizing HC emissions during cold start conditions so that HC emissions can be minimized. A new estimator for A/F of the exhaust gas has been developed. The A/F estimator described in this study utilizes measured exhaust gas temperature and general engine parameters such as engine speed, airflow, coolant temperature, etc.