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This paper describes the use of a modified quasi-dimensional spark-ignition engine simulation code to predict the extent of cycle-to-cycle variations in combustion. The modifications primarily relate to the combustion model and include the following: 1. A flame kernel model was developed and implemented to avoid choosing the initial flame size and temperature arbitrarily. 2. Instead of the usual assumption of the flame being spherical, ellipsoidal flame shapes are permitted in the model when the gas velocity in the vicinity of the spark plug during kernel development is high. Changes in flame shape influence the flame front area and the interaction of the enflamed volume with the combustion chamber walls. 3. The flame center shifts due to convection by the gas flow in the cylinder. This influences the flame front area through the interaction between the enflamed volume and the combustion chamber walls. 4. Turbulence intensity is not uniform in cylinder, and varies cycle-to-cycle.

Gasoline/ethanol fuel blends have significant synergies with Spark Ignited Direct Injected (SI DI) engines. The higher latent heat of vaporization of ethanol increases charge cooling due to fuel evaporation and thus improves knock onset limits and efficiency. Realizing these benefits, however, can be challenging due to the finite time available for fuel evaporation and mixing. A methodology was developed to quantify how much in-cylinder charge cooling takes place in an engine for different gasoline/ethanol blends. Using a turbocharged SI engine with both Port Fuel Injection (PFI) and Direct Injection (DI), knock onset limits were measured for different intake air temperatures for both types of injection and five gasoline/ethanol blends. The superior charge cooling in DI compared to PFI for the same fuel resulted in pushing knock onset limits to higher in-cylinder maximum pressures. Knock onset is used as a diagnostic of charge cooling.

Spark Ignited Direct Injection (SI DI) of fuel extends engine knock limits compared to Port Fuel Injection (PFI) by utilizing the large in-cylinder charge cooling effect due to fuel evaporation. The use of gasoline/ethanol blends in direct injection (DI) is therefore especially advantageous due to the high heat of vaporization of ethanol. In addition to the thermal benefit due to charge cooling, ethanol blends also display superior chemical resistance to autoignition, therefore allowing the further extension of knock limits. Unlike the charge cooling benefit which is realized mostly in SI DI engines, the chemical benefit of ethanol blends exists in Port Fuel Injected (PFI) engines as well. The aim of this study is to separate and quantify the effect of fuel chemistry and charge cooling on knock. Using a turbocharged SI engine with both PFI and DI, knock limits were measured for both injection types and five gasoline-ethanol blends.

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.

The goal of this paper is to quantitatively assess the implications of congressionally mandated biofuel targets on requirements for ethanol blending, distribution, and usage in spark ignition engines in the U.S. light-duty vehicle fleet. The “blend wall” is a term that refers to the maximum amount of ethanol that can be blended into the gasoline pool without exceeding the legal volumetric blend limit of 10%. Beyond the blend wall, the additional ethanol fuel must be used in higher blends of ethanol like E85. Once the blend wall is reached, the existing fleet of flex fuel vehicles (FFVs) will be required to use E85 for some percentage of vehicle miles traveled (VMT) in order to achieve the Renewable Fuel Standard (RFS) targets.

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 four-stroke spark-ignition engine cycle has been developed for studies of the effects of variations in engine design and operating parameters on engine performance, efficiency and NO emissions. The simulation computes the flows into and out of the engine, calculates the changes in thermodynamic properties and composition of the unburned and burned gas mixtures within the cylinder through the engine cycle due to work, heat and mass transfers, and follows the kinetics of NO formation and decomposition in the burned gas. The combustion process is specified as an input to the program through use of a normalized rate of mass burning profile. From this information, the simulation computes engine power, fuel consumption and NO emissions. Predictions made with the simulation have been compared with data from a single-cylinder CFR engine over a range of equivalence ratios, spark-timings and compression ratios.

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.

The wear patterns of the rings and grooves of a diesel engine were analyzed by using a ring dynamics/gas flow model and a ring-pack oil film thickness model. The analysis focused primarily on the contact pressure distribution on the ring sides and grooves as well as on the contact location on the ring running surfaces. Analysis was performed for both new and worn ring/groove profiles. Calculated results are consistent with the measured wear patterns. The effects of groove tilt and static twist on the development of wear patterns on the ring sides, grooves, and ring running surfaces were studied. Ring flutter was observed from the calculation and its effect on oil transport was discussed. Up-scraping of the top ring was studied by considering ring dynamic twist and piston tilt. This work shows that the models used have potential for providing practical guidance to optimizing the ring pack and ring grooves to control wear and reduce oil consumption.

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.

Experiments were conducted to determine the effects of substantial spark retard on combustion, hydrocarbon (HC) emissions, and exhaust temperature, under cold engine conditions. A single-cylinder research engine was operated at 20° C fluid temperatures for various spark timings and relative air/fuel ratios. Combustion stability was observed to decrease as the phasing of the 50% mass fraction burned (MFB) occurred later in the expansion stroke. A thermodynamic burn rate analysis indicated combustion was complete at exhaust valve opening with -20° before top dead center (BTDC) spark timings. Chemical and thermal energy of the exhaust gas was tracked from cylinder-exit to the exhaust runner. Time-resolved HC concentrations measured in the port and runner were mass weighted to obtain an exhaust HC mass flow rate. Results were compared to time averaged well downstream HC levels.

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.

In the study of internal combustion engines, gas temperatures within the system are of significant importance. The adverse conditions under firing operation, however, make measurements by any means very difficult. This current study seems to have gone the farthest to date for velocity of sound gas temperature measurements in internal combustion engine applications. An ultrasound signal is sent by a transmitting transducer, through the gas medium, and into the receiving transducer. The received signal is recorded, and the gas temperature determined from the time of flight. In-cylinder and exhaust manifold gas temperatures under fired conditions are presented, and are all consistent. Impacts of operating parameters like mixture equivalence ratio and coolant temperature are investigated.

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.

A thermodynamic based cycle simulation which uses a thermal boundary layer, either, a fully mixed or layered adiabatic core, and a crevice combustion inefficiency routine has been used to explore the sensitivity of NO concentration predictions to critical physical modeling assumptions. An experimental database, which included measurements of residual gas fraction, was obtained from a 2.0 liter Nissan engine while firing on propane. A model calibration methodology was developed to ensure accurate predictions of in-cylinder pressure and burned gas temperature. Comparisons with experimental NO data then showed that accounting for temperature stratification during combustion with a layered adiabatic core and including a crevice/combustion inefficiency routine, improved the match of modeling predictions to data, in comparison to a fully mixed adiabatic core.

A model has been developed which predicts engine-out hydrocarbon (HC) emissions for spark-ignition engines. The model consists of a set of scaling laws that describe the individual processes that contribute to HC emissions. The model inputs are the critical engine design and operating variables. This set of individual process scaling relations was then calibrated using production spark-ignition engine data at a fixed light-load operating point. The data base consisted of engine-out HC emissions from two-valve and four-valve engine designs with variations in spark timing, valve timing, coolant temperature, crevice volume, and EGR, for five different engines. The model was calibrated separately for the three different engines to accommodate differences in engine design details and to determine the relative magnitudes of each of the major sources. A good fit to this database was obtained.

The oil control ring is the most critical component for oil consumption and friction from the piston system in internal combustion engines. Three-piece oil control rings are widely used in Spark Ignition (SI) engines. However, the dynamics and lubrication of three piece oil control rings have not been thoroughly studied from the theoretical point of view. In this work, a model was developed to predict side sealing, bore sealing, friction, and asperity contact between rails and groove as well as between rails and the liner in a Three Piece Oil Control Ring (TPOCR). The model couples the axial and twist dynamics of the two rails of TPOCR and the lubrication between two rails and the cylinder bore. Detailed rail/groove and rail/liner interactions were considered. The pressure distribution from oil squeezing and asperity contact between the flanks of the rails and the groove were both considered for rail/groove interaction.

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.

The development of a cycle simulation model for the jet ignition prechamber stratified charge engine is described. Given the engine geometry, load, speed, air-fuel ratios and pressures and temperatures in the two intakes, flow ratio and a suitable combustion model, the cycle simulation predicts engine indicated efficiency and NO emissions. The relative importance of the parameters required to define the combustion model are then determined, and values for ignition delay and burn angle are obtained by matching predicted and measured pressure-time curves. The variation in combustion parameters with engine operating variables is then examined. Predicted and measured NO emissions are compared, and found to be in reasonable agreement over a wide range of engine operation. The relative contribution of the prechamber NO to total exhaust NO is then examined, and in the absence of EGR, found to be the major source of NO for overall air-fuel ratios leaner than 22:1.