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This paper presents a thermodynamics-based mean-value engine model that predicts the temperature and pressure at the end of each discrete combustion phase, the peak temperature and pressure, and the indicated mean effective pressure. The model has sensitivities to the engine speed, the main and pilot injection quantities and timings, and the temperature and pressure conditions in the intake and exhaust manifolds. Mathematical relationships are established between the input variables and the output variables through the thermodynamic principles of the modified ideal-gas-limited pressure cycle. Modifications to the ideal-gas cycle include the pilot combustion stage, the effective compression ratio based on the fuel injection timing and start of combustion, the effect of the constant-volume burn ratio on combustion, and the exhaust valve opening timing. The model is also augmented with empirical correlations for the ignition delay, the constant-volume burn ratio, and the heat transfer in order to improve the fidelity of the model. It is validated using test data from a Ford 6.7 l diesel engine. Unlike most data-regression-based mean-value engine models, the model presented in this paper does not sacrifice essential details of the underlying physics while providing a computationally efficient simulation tool.

This paper presents a multi-parameter investigation of Al2O3 nano-particles dispersed in distilled water, ethylene glycol and ethylene glycol–distilled water mixture (50/50 vol.%). The nano-fluid samples were prepared with ultrasonic processing with particle concentration up to 9 wt.%. Samples were characterized by transmission electron microscope imaging, particle surface charge (zeta potential), particle aggregate size, light absorbance and pH. The thermal conductivity and viscosity of the nano-fluid samples were measured. 10.9% enhancement in thermal conductivity was observed in ethylene glycol–distilled water mixture based nano-fluid with 5 wt.% Al2O3 nano-particle loading. The results show multiple-perspective correlations between nano-fluid characteristics and thermal properties. The findings are summarized as follows. Combined effect of base fluid viscosity and particle surface charge determines the degree of nano-particle aggregation. Higher enhancement in thermal conductivity is observed with moderate particle aggregation, while either light or heavy aggregation lowers the enhancement. The ethylene glycol–water mixture based nano-fluids show overall higher thermal conductivity enhancement than the distilled water and ethylene glycol based nano-fluids. The degradation of nano-fluid thermal conductivity enhancement over time is found to be related to the gravity-driven particle sedimentation. Nano-fluids containing larger particle aggregates show higher viscosity augmentation. However, the extent of viscosity augmentation is not proportional to the extent of particle aggregation.

An empirical ignition delay model has been developed for the fuel blends of isooctane, n-heptane, toluene and ethanol based on their molar fractions in the stoichiometric condition. The model employs traditional Arrhenius type correlation and cool-flame temperature rise correlations to describe the negative temperature coefficient (NTC) region for the fuel blends. The overall ignition delay of a fuel blend is correlated with individual ignition delay information based on the molar fraction of the fuel component in the mixture. The proposed model is successfully validated against the published experimental ignition delay data using various binary, ternary and quaternary fuel blends of isooctane, n-heptane, toluene and ethanol.

Diesel/natural gas dual-fuel engines were studied numerically using Latin hypercube sampling (LHS) and multi-objective Pareto optimization. The combustion characteristics were analyzed and performance metrics studied as a function of the exhaust gas recirculation (EGR) fraction, compression ratio, injection timing, and natural gas fraction (NGF). The fundamental effects of the NGF on the in-cylinder pressure, peak temperature, brake torque, and brake specific fuel consumption (BSFC) were investigated. Regression coefficients were obtained using LHS to describe the sensitivity of the brake torque, BSFC, and brake specific NOX (BSNOX) emission levels to the operating parameters. A response surface was found using Pareto optimization. The dominant parameters affecting the brake torque, BSFC, and BSNOX were the compression ratio and EGR fraction.

A spray and evaporation model has been developed and embedded in a quasi-dimensional multi-zone direct injection internal combustion engine simulation framework. The model accounts for the behavior of the spray zone and fuel evaporation including sub-models for spray breakup, improved zone velocity estimations with transient fuel injection, spray penetration and tracking of evaporated fuel components. Each sub-model deals with multi-component fuel surrogates to simulate the real fuel effects. To enhance sensitivity of the model to the fuel components, additional thermophysical properties to the traditional spray model are incorporated. The ideal gas and the ideal solution are assumed in the model to retain computational efficiency. Finally, the model was validated against experiments and compared with other numerical methods. The ability of the new model to treat a multi-component fuel provides an improvement in the simulations of modern direct injection internal combustion engine when used with alternative fuels.

An analytic multi-dimensional dynamic model of a membrane type humidifier has been developed for the study of transient responses of the humidifier under proton exchange membrane fuel cell vehicle operating conditions. The dynamic responses of heat and mass transfer and fluid flow in a membrane humidifier are mathematically formulated and modeled with a newly developed pseudo-multi-dimensional concept. The model is used to analyze the performance of the humidifier under various operating conditions and the dynamic response of the humidifier under transient operating conditions. The simulation results show that, in the case of the water-to-gas type membrane humidifier modeled in this study, the time constant of water diffusion in the membrane is less than 1 s. Thus, the delay of the response of the humidifier induced by the vapor diffusion in the membrane is not significant in vehicle operation. However, it is also found that the dynamic behavior is mainly due to the thermal resistance and heat capacity of the membrane humidifier.

Computationally efficient numerical models of battery cooling systems are developed and the effects of the battery cell arrangement and the heat transfer fluid (HTF) type on the cooling performance and the parasitic power consumption of the system are investigated. A one-dimensional heat conduction model of a cylindrical battery cell is developed using a finite difference method for the cell temperature prediction and a battery module model is developed to predict the cell to cell temperature variation and the power consumption of the systems depending on the design of battery module and operating conditions. The analysis of the battery thermal management system (BTMS) design by using the numerical model is conducted for air and liquid type BTMSs. From the numerical analysis, it is found that a wide battery module with a small cell to cell gap is desirable for the air type BTMS while a narrow battery module with a small gap is desirable for a liquid type BTMS. The results also show that the air type BTMS consumes much more power compared with the liquid type BTMS especially for high heat load condition. However, under low heat load conditions, the power consumption of the air type BTMS is acceptable considering its advantages over the liquid type BTMS.

A numerical engine mapping methodology is proposed for the engine performance and fuel consumption map generation. An integrated model is developed by coupling a single cylinder GT-Power® engine model with a MATLAB/ Simulink® based boost system model to simulate a turbocharged diesel engine over the entire engine operating speed and load ranges within reasonable computational constraints. A single cylinder engine model with the built-in multi-zone combustion modeling option in GT-Power® is configured as a predictive engine model. The cycle averaged simulation result from the engine model is used as the boundary conditions of the boost system including intake and exhaust manifolds and a turbocharger. The boost system model developed in MATLAB/Simulink® platform calculates the intake and exhaust conditions which are fed back to the engine model. The integrated system model predicts the performance and fuel consumption of a turbocharged diesel engine with better predictive capability than mean value engine models. Its computational time is fast enough to simulate the engine over the entire engine operation range compared to multi-cylinder engine models.

Heat transfer is one of the major factors affecting the performance, efficiency, and emissions of internal combustion engines. As convection heat transfer is dominant in engine heat transfer, accurate modelling of the boundary layer heat transfer is required. In engine computational fluid dynamics (CFD) simulations, the wall function approach has been widely used to model the near-wall flow and temperature field. The present paper suggests a modified wall function approach to model heat transfer in internal combustion engines. Special emphasis has been placed on introducing the effect of variable density and variable viscosity in the model formulation. A non-dimensional temperature corrector is suggested to incorporate the variable density effect on the wall function approach. The suggested model is applied in KIVA-3V and is validated against experimental data of a homogeneous charge compression-ignition engine, showing improved predictions for pressure and emissions compared with the standard wall function model.

A fuel cell system model with detailed cooling module model was developed to evaluate the control algorithms of cooling module which is used for the thermal management of a proton exchange membrane fuel cell (PEMFC) system. The system model is composed of a dynamic fuel cell stack model and a detailed dynamic cooling module model. To extend modeling flexibility, the fuel cell stack model utilizes analytic approach to capture the transient behavior of the stack temperature corresponding to the change of the coolant temperature and the flow rate during load follow-up. The cooling module model integrated model of fan, water pump, coolant passage, and electric motors so that the model is capable of investigation of operating strategy of pump and fan. The fuel cell system model is applied to the investigation of the control logics of the cooling module. Since, it is necessary for the control of cooling module to define the reference conditions such as coolant temperature and fuel cell stack temperature, this study presents such thermal management criteria. Finally, two control algorithms were compared, a conventional control algorithm and a feedback control algorithm. As a consequence, the feedback control algorithm was found to be more suitable for the cooling module of the PEMFC stack, as they consume less parasitic power while producing more stack power compared to a conventionally controlled cooling module.

Proton exchange membrane (PEM) fuel cells for transportation applications have relatively large active areas to meet the power demand and they require thermal management not only to maintain a proper operating temperature but also to manage the temperature distribution within the fuel cell. In this study, a thermal model of a PEM fuel cell and a thermal management system has been developed to investigate the criteria of thermal management and develop a thermal management strategy for fuel cells with large active cell areas. The fuel cell model consists of three sub-models to simulate the temperature-sensitive electrochemical reaction and capture the thermal management effect on the performance; a water transport model, an agglomerate structure electrochemistry model and a two-dimensional heat transfer model. The thermal management system model including radiator, cooling pump and fan is also employed for the investigation of the trade-off between the temperature distribution effect and the parasitic loss. The fuel cell operating temperature as a criterion for the thermal management is discussed related to the membrane durability and the safety margin during transient operations. Thermal management strategy for minimum cooling parasitic loss is proposed based on the simulation results in conjunction with the criterion of the operating temperature.

The geometric effects of the abrasive flow machining (AFM), a surface finishing process, on a direct-injection diesel fuel injector nozzle are studied and characterized in this study. To measure the microscopic variations inside the nozzle, before and after the AFM process, several different geometry characterization techniques are used. Empirical correlations that relate nozzle geometrical changes to the AFM process period are derived from the measurements. The resulting impact of the geometric changes of the nozzle on the engine performance and emissions are also assessed with a numerical engine cycle simulation model that is based on a quasi-dimensional multi-zone diesel spray combustion model. This study shows that properly AFM-processed injectors can enhance the engine performance and improve the emissions due to the improved quality of the nozzle characteristics. However, extended process can also cause the enlargement of the nozzle as a side effect and this can adversely affect emissions. Since the enlargement of the nozzle is unavoidable, yet must be minimized, strict control over the process is required. This control can be enforced by either limiting the AFM process, or properly preparing the initial nozzle diameter so as to accommodate the inevitable changes of nozzle geometry.

The effects of the Abrasive Flow Machining (AFM) process on a direct injection (DI) Diesel engine fuel injector nozzle are studied. Geometry characterization techniques were developed to measure the microscopic variations inside the nozzle before and after the process. This paper also provides empirically-based correlations of the nozzle geometry changes due to the AFM process. The resulting impact of the process on the engine performance and emissions are also assessed with a DI Diesel engine test setup. This study shows that properly AFM-processed injectors can enhance engine performance and improve emissions due to the improved quality of the nozzle characteristics. However, an extended process can also cause enlargement of the nozzle hole as a side effect, which can adversely affect emissions. Emission measurements show the trade-off for the minimum levels as the process proceeds. Since the enlargement of the hole during the AFM process is not avoidable and must be minimized, strict control over the process is required. This control can be enforced by either limiting the AFM processing period, or by properly preparing the initial hole diameter so as to accommodate the inevitable changes in the nozzle geometry.

The predictive capability of the engine cycle simulation previously developed on the basis of a reduced quasi—dimensional combustion model has been enhanced by introducing a new submodel that correlates the discharge coefficient of the injector nozzle with the design variables of the nozzle and injection conditions. This enhancement enables prediction of the effect of microvariations in the injector nozzle hole geometry as well as the variations in the main design parameters on diesel spray evolution and combustion processes. As a result, the engine cycle simulation model can predict changes in engine performance and emissions due to injector nozzle design changes. First, the effect of the chamfer radius of the injector nozzle inlet on the discharge coefficient at various injection pressures was explored by simulating fuel injection in a constant—pressure vessel. The results showed that a larger chamfer radius improves the discharge coefficient and the rounded nozzle inlet can also reduce injector—to—injector variation. A case study of the injector nozzle hole design optimization was also performed for several different objectives to demonstrate the usage of the engine cycle simulation as a simulation tool. The case study showed that an optimized injector hole diameter depends on the objective while a larger chamfer radius, in general, helps to improve both engine performance and emissions.

Models for ignition delay in a direct injection compression ignition engine are investigated and fuel specific properties are included to predict the effects of different fuels on the ignition delay. These models follow the Arrhenius type expression for the ignition delay modified with the oxygen concentration and Cetane number to extend the range of validity. In this investigation two fuel-sensitive spray ignition delay models are developed: a global model and a local model. The global model is based on the global combustion chamber charge properties including temperature, pressure and oxygen/fuel content. The local model is developed to account for temporal and spatial variations in properties of separated spray zones such as local temperature, oxidizer and fuel concentrations obtained by a quasi-dimensional multi-zone fuel spray model. These variations are integrated in time to predict the ignition delay. An ignition delay model is typically re-calibrated for a specific fuel being used. In this study, the global ignition delay model includes the Cetane number to capture ignition delay of various fuels. The local model uses Cetane number and local stoichiometric oxygen to fuel molar ratio. Due to those variables, the model is capable of predicting spray ignition delays for a set of fuels with a single calibration step. Experimental dataset of spray ignition delay in a constant volume chamber is used for model development and calibration. The models show a good accuracy for the predicted ignition delay of four different fuels: JP8, DF2, n-heptane and n-dodecane. The investigation revealed that the most accurate form of the models is from a calibration done for each individual fuel with only a slight decrease in accuracy when a single calibration is done for all fuels. The single calibration case is the more desirable outcome as it leads to general models that cover all the fuels. Of the two proposed models the local model has a slightly better accuracy compared to the global model. Results for both models demonstrate the improvements that can be obtained for the ignition delay model when additional fuel specific properties are included in the spray ignition model.Other alternative fuels like synthetic oxygenated fuels were included in the investigation. These fuels behave differently such that the Cetane number does not provide the same explanation for the trend in ignition delay. Though of lower accuracy, the new models do improve the predictive capability when compared with existing types of ignition delay models applied to this kind of fuels.Copyright © 2014 by ASME

In this study we report the development and validation of phenomenological models for predicting direct injection (DI) diesel engine emissions, including nitric oxide (NO), soot, and unburned hydrocarbons (HC), using a full engine cycle simulation. The cycle simulation developed earlier by the authors (D. Jung and D. N. Assanis, 2001, SAE Transactions: Journal of Engines, 2001-01-1246) features a quasidimensional, multizone, spray combustion model to account for transient spray evolution, fuel–air mixing, ignition and combustion. The Zeldovich mechanism is used for predicting NO emissions. Soot formation and oxidation is calculated with a semiempirical, two-rate equation model. Unburned HC emissions models account for three major HC sources in DI diesel engines: (1) leaned-out fuel during the ignition delay, (2) fuel yielded by the sac volume and nozzle hole, and (3) overpenetrated fuel. The emissions models have been validated against experimental data obtained from representative heavy-duty DI diesel engines. It is shown that the models can predict the emissions with reasonable accuracy. Following validation, the usefulness of the cycle simulation as a practical design tool is demonstrated with a case study of the effect of the discharge coefficient of the injector nozzle on pollutant emissions.

A new concept of reduced quasi-dimensional combustion model for a direct injection diesel engine is developed based on the previously developed quasi-dimensional multi-zone model to improve the computational efficiency. In the reduced model, spray penetration and air entrainment are calculated for a number of zones within the spray while three zones with aggregated spray zone concept are used for the calculation of spray combustion and emission formation processes. It is also assumed that liquid phase fuel appears only near the nozzle exit during the breakup period and that spray vaporization is immediate in order to reduce the computational time. Validation of the reduced model with experimental data demonstrated that the new model can predict engine performance and NO and soot emissions reasonably well compared to the original model. With the new concept of reduced model, computational efficiency is significantly improved as much as 200 times compared to the original model.

Internal combustion (IC) engines experience in-cylinder gas temperatures of up to 2500°C during combustion, promoting heat transfer from the hot gases to the metal surfaces of the combustion chamber. Heat needs to be removed at relatively high rates to maintain proper engine component temperatures, and prevent failures that result from excessive thermal stresses, fatigue cracking, engine knocking combustion, and lubricant layer degradation. The engine cooling system accomplishes the necessary heat rejection by circulating air or liquid coolant around the combustion chamber, absorbing heat from the engine, and subsequently dissipating the heat to the ambient. Heat rejection to the lubricant plays an important role too. A thorough understanding of heat transfer modes and pathways is necessary for the design of an effective engine cooling system. The topics covered in this chapter are modes of engine heat transfer, modeling and experimental analysis of the heat transfer from the gas in the cylinder to the wall, heat transfer from the outer wall to coolant, semiempirical heat transfer correlations for engine cycle simulations, heat transfer from the piston rings to the cylinder liner, exhaust port heat transfer, cooling system functional requirements, air cooling, liquid cooling, coolant flow patterns through the cylinder block/head, cooling system components, temperature control in the engine with liquid cooling, automatic transmission cooling, as well as cooling system operation, integration, packaging, and management of the underhood air flow. Waste heat recovery is discussed at the end of the chapter as a special topic. Keywords: IC engine; cooling; heat transfer; conduction; convection; radiation; heat flux measurement; thermal management; waste heat recovery

Models for ignition delay in a direct injection compression ignition engine are investigated and fuel specific properties are included to predict the effects of different fuels on the ignition delay. These models follow the Arrhenius type expression for the ignition delay modified with the oxygen concentration and Cetane number to extend the range of validity. In this investigation two fuel-sensitive spray ignition delay models are developed: a global model and a local model. The global model is based on the global combustion chamber charge properties including temperature, pressure and oxygen/fuel content. The local model is developed to account for temporal and spatial variations in properties of separated spray zones such as local temperature, oxidizer and fuel concentrations obtained by a quasi-dimensional multi-zone fuel spray model. These variations are integrated in time to predict the ignition delay. An ignition delay model is typically re-calibrated for a specific fuel being used. In this study, the global ignition delay model includes the Cetane number to capture ignition delay of various fuels. The local model uses Cetane number and local stoichiometric oxygen to fuel molar ratio. Due to those variables, the model is capable of predicting spray ignition delays for a set of fuels with a single calibration step. Experimental dataset of spray ignition delay in a constant volume chamber is used for model development and calibration. The models show a good accuracy for the predicted ignition delay of four different fuels: JP8, DF2, n-heptane and n-dodecane. The investigation revealed that the most accurate form of the models is from a calibration done for each individual fuel with only a slight decrease in accuracy when a single calibration is done for all fuels. The single calibration case is the more desirable outcome as it leads to general models that cover all the fuels. Of the two proposed models the local model has a slightly better accuracy compared to the global model. Results for both models demonstrate the improvements that can be obtained for the ignition delay model when additional fuel specific properties are included in the spray ignition model. Other alternative fuels like synthetic oxygenated fuels were included in the investigation. These fuels behave differently such that the Cetane number does not provide the same explanation for the trend in ignition delay. Though of lower accuracy, the new models do improve the predictive capability when compared with existing types of ignition delay models applied to this kind of fuels.

New capabilities for simulating a tracked vehicle are presented, including an advanced dynamic track model, a high-fidelity diesel engine system model, and an integration scheme to perform a coupled simulation of vehicle/powertrain dynamics. These capabilities are essential for understanding the interplay of vehicle dynamics and powertrain dynamics, including track vibration (and durability). Suspension response and engine performance. The dynamic track model considers the track as an equivalent continuum and captures longitudinal and transverse track vibrations, static sag, and superposed translation. A low-order discrete model is developed by employing modal track coordinates. The continuum approximation for the track is validated through experiments on a representative track span. This track model is extended and implemented into a commercial multibody dynamics code—DADS—through development of a new user-support-force element that integrates the track element with the vehicle hull and suspensi...

A thermodynamics-based computationally efficient mean value engine model that computes ignition delay, combustion phases, exhaust temperature, and indicated mean effective pressure has been developed for the use of control strategy development. The model is derived from the thermodynamic principles of ideal gas standard limited pressure cycle. In order to improve the fidelity of the model, assumptions that are typically used to idealize the cycle are modified or replaced with ones that more realistically replicate the physical process such as exhaust valve timing, in-cylinder heat transfer, and the combustion characteristics that change under varying engine operating conditions. The model is calibrated and validated with the test data from a Ford 6.7 liter diesel engine. The mean value model developed in this study is a flexible simulation tool that provides excellent computational efficiency without sacrificing critical details of the underlying physics of the diesel combustion process.

A Physics-based mean value model that predicts engine combustion, heat transfer, gas exchange, and friction loss has been developed. The model is developed starting from the thermodynamic principles of an ideal gas standard limited pressure cycle concept. The idealized assumptions that are typically used in a limited pressure cycle concept are relieved to enhance the fidelity of the model by introducing variables that account for the in-cylinder heat transfer and the combustion characteristics that change under varying EGR rate as well as the engine speed and load while minimal number of empirical correlations are used to ensure the compactness and flexibility of the physics-based mean value model. The model is calibrated and validated with the simulation results from a detailed GT-Power® engine model previously calibrated with experimental results from a Ford 6.7 liter Diesel engine. The comparison shows good agreement between the results from the mean value model and the GT-Power® model. The mean value model developed in this study is a flexible simulation tool that provides excellent computational efficiency without sacrificing critical physical details of the Diesel combustion process required by the control design development.

In this study, numerical simulations of the vehicle cooling system and the vehicle powertrain system of a virtual heavy duty tracked series hybrid electric vehicle (SHEV) is developed to investigate the thermal responses and power consumptions of the cooling system. The output data from the powertrain system simulation are fed into the cooling system simulation to provide the operating conditions of powertrain components. Three different cooling system architectures constructed with different concepts are modeled and the factors that affect the performance and power consumption of each cooling system are identified and compared with each other. The results show that the cooling system architecture of the SHEV should be developed considering various cooling requirements of powertrain components, power management strategy, performance, parasitic power consumption, and the effect of driving conditions. It is also demonstrated that a numerical model of the SHEV cooling system is an efficient tool to assess design concepts and architectures of the system during the early stage of system development.

Positive displacement pumps are used in automotive transmissions to provide pressurized fluid to various hydraulic components in the transmission and also lubricate the mechanical components. The output flow of these pumps increases with speed, almost linearly, but the flow requirements often saturate at higher speeds resulting in the excess flow draining back to the sump. This represents a parasitic loss in the transmission leading to a loss in fuel economy. To overcome this issue, variable displacement pumps have been used in the transmission, where the output flow is reduced by controlling the displacement of the pump. The use of these pumps in automatic transmissions, has resulted in better fuel economy as compared to some types of fixed displacement pumps. However, the literature does not fully explore the benefits of variable displacement pumps to a specific type of transmission namely, dual-clutch transmission, that has different pressure & flow requirements than an epicyclic gear-train. This paper presents an analysis on the effect of pump selection on fuel economy in a five speed dual clutch transmission of a commercial vehicle. Models of the engine, transmission & vehicle are developed along with the models of two different types of pumps: a fixed displacement gerotor pump and a variable displacement vane pump. The models are then parameterized using experimental data and the fuel economy of the vehicle is simulated on a standard driving cycle. The results suggest that the fuel economy benefit obtained by the use of the variable displacement pump in dual clutch transmissions is comparable to that of automatic transmissions.

The cooling system of Series Hybrid Electric Vehicles (SHEVs) is more complicated than that of conventional vehicles due to additional components and various cooling requirements of different components. In this study, a numerical model of the cooling system for a SHEV is developed to investigate the thermal responses and power consumptions of the cooling system. The model is created for a virtual heavy duty tracked SHEV. The powertrain system of the vehicle is also modeled with Vehicle-Engine SIMulation (VESIM) previously developed by the Automotive Research Center at the University of Michigan. VESIM is used for the simulation of powertrain system behaviors under three severe driving conditions and during a realistic driving cycle. The output data from VESIM are fed into the cooling system simulation to provide the operating conditions of powertrain components. The cooling system model includes various component models for three main fluid circuits of coolant, cooling air, and engine oil. The model predicts the thermal responses of all cooling system components and the temperatures of the engine and electric components. Using the cooling system models, the thermal response and power consumption of the cooling system over a realistic driving cycle is estimated and the factors that affect the performance and the power consumption of the cooling system are identified.

A numerical model of a proton exchange membrane fuel cell has been developed to predict the performance of a large active area fuel cell with the water cooling thermal management system. The model includes three submodels for water transport, electrochemical reaction, and heat transfer. By integrating those submodels, local electric resistance and overpotential depending on the water and temperature distribution can be predicted. In this study the effects of the inlet gas temperature and humidity on the fuel cell performance are explored, and the effect of the temperature distribution at different coolant temperatures is investigated. The results show that the changes in local electric resistance due to temperature distribution cause fuel cell power decrease. Therefore, the coolant temperature and flow rate should be controlled properly depending on the operating conditions in order to minimize the temperature distribution while maximizing the power output of the fuel cell.

Diesel engines are gaining in popularity, penetrating even the luxury and sports vehicle segments that have traditionally been strongly favored gasoline engines as the performance and refinement of diesel engines have improved significantly in recent years. The introduction of sophisticated technologies such as common rail injection (CRI), advanced boosting systems such as variable geometry and multi-stage turbocharging, and exhaust gas after-treatment systems have renewed the interest in Diesel engines. Among the technical advancements of diesel engines, the multi-stage turbocharging is the key to achieve such high power density that is suitable for the luxury and sports vehicle applications. Single-stage turbocharging is limited to roughly 2.5 bar of boost pressure. In order to raise the boost pressure up to levels of 4 bar or so, another turbocharger must be connected in series further multiplying the pressure ratio. The dual-stage turbocharging, however, adds system complexity, and the matching of two turbochargers becomes very costly if it is to be done experimentally. This study presents a simulation-based methodology for dual-stage turbocharger matching through an iterative procedure predicting optimal configurations of compressors and turbines. A physics-based zero-dimensional Diesel engine system simulation with a dual-stage turbocharger is implemented in SIMULINK environment, allowing easy evaluation of different configurations and subsequent analysis of engine system performance. The simulation program is augmented with a turbocharger matching program and a turbomachinery scaling routine. The configurations considered in the study include a dual-stage turbocharging system with a bypass valve added to the high pressure turbine, and a system with a wastegate valve added to a low-pressure turbine. The systematic simulation study allows detailed analysis of the impact of each of the configurations on matching, boost characteristics and transient response. The configuration with the bypass valve across high pressure turbine showed better results in terms of both steady state engine torque and transient behavior.

This paper describes a test cell setup for concurrent running of a real engine and a vehicle system simulation, and its use for evaluating engine performance when integrated with a conventional and a hybrid electric driveline/vehicle. This engine-in-the-loop (EIL) system uses fast instruments and emission analyzers to investigate how critical in-vehicle transients affect engine system response and transient emissions. Main enablers of the work include the highly dynamic AC electric dynamometer with the accompanying computerized control system and the computationally efficient simulation of the driveline/vehicle system. The latter is developed through systematic energy-based proper modeling that tailors the virtual model to capture critical powertrain transients while running in real time. Coupling the real engine with the virtual driveline/vehicle offers a chance to easily modify vehicle parameters, and even study two different powertrain configurations. In particular, the paper describes the engine-in-the-loop study of a V8, 6L engine coupled to a virtual 4x4 HighMobility Multipurpose Wheeled Vehicle (HMMWV). The results shed light on critical transients in a conventional powertrain and their effect on NOx and soot emissions. Next, the conventional HMMWV powertrain is replaced with a parallel hybrid electric configuration and two power management strategies are examined. Comparison of the conventional and hybrid propulsion options provides detailed insight into fuel economy – emissions tradeoffs at the vehicle level.

A thermal model of the Proton Exchange Membrane Fuel Cell (PEMFC) was developed to investigate the performance of a large active area fuel cell with the water cooling thermal management system. The model includes three sub-models: water transport model, electrochemical reaction model and heat transfer model. The water transport model calculates water distribution and the electric resistance of the membrane electrolyte. The electrochemical reaction model for the agglomerate structure cathode catalyst layer predicts the cathode overpotentials including mass transport limitation effect at high current density region. Two-dimensional heat transfer model incorporated with coolant and gas channels predicts the temperature distribution within the fuel cell. By integrating those sub-models, local electric resistance and overpotentials depending on the water and temperature distribution can be predicted. The model was calibrated with published experimental data and sensitivity studies were performed. The effects of the inlet gas temperature and humidity on the fuel cell performance were explored. In addition, the effect of the temperature distribution, and accordingly the electric resistance distribution within the fuel cell depending on the coolant temperature and flowrate was investigated. The results shows that the change in the local electric resistance due to temperature distribution eventually causes fuel cell power decrease and it is also concluded that the coolant temperature and flowrate should be controlled properly depending on the operating conditions in order to minimize the temperature distribution while maximizing power output of the fuel cell.Copyright © 2006 by ASME

This paper investigates the effects of manufacturing variations in fuel injectors on the engine performance with emphasis on emissions. The variations are taken into consideration within a Reliability-Based Design Optimization (RBDO) framework. A reduced version of Multi-Zone Diesel engine Simulation (MZDS), MZDS-lite, is used to enable the optimization study. The numerical noise of MZDS-lite prohibits the use of gradient-based optimization methods. Therefore, surrogate models are developed to filter out the noise and to reduce computational cost. Three multi-objective optimization problems are formulated, solved and compared: deterministic optimization using MZDS-lite, deterministic optimization using surrogate models and RBDO using surrogate models. The obtained results confirm that manufacturing variation effects must be taken into account in the early product development stages.

The engine cooling system for a typical class 3 pickup truck with a medium duty diesel engine was modeled with a commercial code, GT-Cool in order to explore the benefit of controllable electric pump on the cooling performance and the fuel economy. As the first step, the cooling system model with a conventional mechanical coolant pump was validated with experimental data. After the model validation, the mechanical pump sub-model was replaced with the electric pump submodel and then the potential benefit of the electric pump on fuel economy was investigated with the simulation. Based on coolant flow analysis the modified thermostat hysteresis was proposed to reduce the recirculating flow and electric pump effort, thus enabling assessment of the full power saving potential. It was also demonstrated that the radiator size could be reduced without any cooling performance penalty by replacing mechanical pump with the electric pump and decoupling of the pump speed from engine speed. The predicted results indicate that the cooling system with the electric pump can dramatically reduce the pump power consumption during the FTP 74 driving schedule and that radiator can be down-sized by more than 27% of the original size under grade load condition.Copyright © 2004 by ASME

A quasi -dimensional, multi-zone, direct injection (DI) diesel combustion model has been developed and implemented in a full cycle simulation of a turbocharged engine. The combustion model accounts for transient fuel spray evolution, fuel-air mixing, ignition, combustion and NO and soot pollutant formation. In the model, the fuel spray is divided into a number of zones, which are treated as open systems. While mass and energy equations are solved for each zone, a simplified momentum conservation equation is used to ca lculate the amount of air entrained into each zone. Details of the DI spray, combustion model and its implementation into the cycle simulation of Assanis and Heywood [1] are described in this paper. The model is validated with experimental data obtained in a constant volume chamber and engines. First, predictions of spray penetration and spray angle are validated against measurements in a pressurized constant volume chamber. Subsequently, predictions of heat release rate, as well as NO and soot emissions are compared with experimental data obtained from representative heavy-duty, turbocharged diesel engines. It is demonstrated that the model can predict the rate of heat release and engine performance with high fidelity. However, additional effort is require d to enhance the fidelity of NO and soot predictions across a wide range of operating conditions.

A thermodynamics-based Vehicle Thermal Management System (VTMS) model for a heavy-duty, off-road vehicle with a series hybrid electric powertrain is developed for analysing thermal behaviour and investigating power consumption under different vehicle driving conditions. The developed model is first used to define an acceptable and reasonable VTMS configuration; design space exploration techniques are then applied to determine optimal component sizes subject to performance and geometry constraints.