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Autoignition correlations are widely used to predict knock in internal combustion engines as opposed to detailed kinetics mechanisms involving hundreds of reactions due to computational cost. Several autoignition correlations exist in the literature for different fuels, and their functional form depends on the operating parameters like fuel type and temperature range, among other things. In the literature different types of correlations are proposed for gasoline fuel, but to the best of the authors’ knowledge none of these correlations can be used for gasoline-ethanol blends with varying levels of ethanol percentage and a wide range of equivalence ratios and temperatures. In this paper, a new empirical correlation is developed to predict the autoignition of gasoline-ethanol blends over a wide range of temperatures including Negative Temperature Coefficient (NTC) region.

Numerical simulation of in-cylinder processes can significantly reduce the development and refinement costs of engines. While it can be argued that higher fidelity models improve accuracy of prediction, it comes at the expense of high computational cost. In this respect, a 3D analysis of in-cylinder processes may not be feasible for evaluating large number of design and operating conditions. The situation can be more foreboding for transient simulations. In the current work a phenomenological combustion modeling approach is explored that can be implemented in a lower fidelity modeling framework and can approach the accuracy of higher dimensional models with significant reduction in computational cost. The proposed model uses transported probability density function (tPDF) method within a 0D framework to provide a computationally efficient solution while capturing the essential physics of in-cylinder combustion.

In this paper, a fuel tank evaporation/condensation model was developed, which was suitable for calculation of evaporative emissions in a fuel tank. The model uses a diffusion-controlled mass transfer approach in the form of Fick's second law in order to calculate the average concentration of fuel vapor above the liquid level and its corresponding evaporation rate. The partial differential equation of transient species diffusion was solved using a separation of variables technique with the appropriate boundary conditions for a fuel tank. In order to simplify the solution, a quasi-steady assumption was utilized and justified. The fuel vapor pressure was modeled based on an American Petroleum Institute (API) procedure using either a distillation curve or a Reid Vapor Pressure (RVP) as an experimental input for the specific fuel used in the system.

The turbulent flow field inside the cylinder plays a major role in spark ignition (SI) engines. Multiple phenomena that occur during the high pressure part of the engine cycle, such as early flame kernel development, flame propagation and gas-to-wall heat transfer, are influenced by in-cylinder turbulence. Turbulence inside the cylinder is primarily generated via high shear flows that occur during the intake process, via high velocity injection sprays and by the destruction of macro-scale motions produced by tumbling and/or swirling structures close to top dead center (TDC) . Understanding such complex flow phenomena typically requires detailed 3D-CFD simulations. Such calculations are computationally very expensive and are typically carried out for a limited number of operating conditions. On the other hand, quasi-dimensional simulations, which provide a limited description of the in-cylinder processes, are computationally inexpensive.

Recently there has been a substantial interest in adopting asymmetric geometry design inside wall-flow diesel particular filters (DPFs) with larger inlet channel width to accommodate soot/ash accumulation and to reduce back pressure and thus to increase filter operation life time. The current work is sought to develop a model based approach to investigate various aspects of this strategy and to compare results with conventional channel design. This paper describes assumptions and modeling methodologies used to evaluate the impact of asymmetries arising out of geometric design as well as due to ash deposition/accumulation on the overall pressure drop across the filter. Special attention is given to the challenges and strategies associated with flow and thermal solutions (during soot loading or regeneration) since transient ash accumulation causes a time varying reduction of effective wall-flow filtration length.

It has recently been suggested in an experimental study that an aged DOC could be net consumer of engine out NO2 (Katare et al, 2007) thus inhibiting the fast reaction (2NH3 + NO + NO2 => 2N2+3H2O) in an SCR that might follow. Both engine test and flow reactor results indicated that at low temperatures CO and HC reduces NO2 to NO and that CO is much better reductant than HC. The present study investigates the mechanistic story behind this experimentally observed phenomenon by means of a global reaction mechanism. It also investigates the role of CO inhibition of NO oxidation at higher temperature which also plays key role in the overall oxidation efficiency of a DOC. Once a suitable mechanism is defined by comparing against measurements, the current study will use it to examine conditions under which DOC can destroy NO2 and to propose possible strategies to avoid NO2 consumption in order to obtain high SCR efficiency.

Engines and vehicle systems are becoming increasing complex partly due to the incorporation of emission abatement components as well as control strategies that are technologically evolving and innovative to keep up with emissions requirements. This makes the testing and verification with actual prototypes prohibitively expensive and time-consuming. Consequently, there is an increasing reliance on Software-In-the-Loop (SIL) and Hardware-In-the-Loop (HIL) simulations for design evaluation of system concepts. This paper introduces a methodology in which detailed chemical kinetic models of catalytic converters are transformed into fast running models for control design, calibration or real time ECU validation. The proposed methodology is based on the use of a hybrid, structured, semi-automatic scheme for reducing high-fidelity models into fast running models.

This article describes a system level 1D simulation tool that has been constructed on the Quasi-steady (QS) method. By assuming that spatial changes are much greater than the temporal ones, rigorous 1D governing equations can be considerably simplified thus becoming less computationally demanding to solve and therefore suitable for control oriented modeling purposes. With the proposed tool exhaust pipe wall temperature profiles, including multiple-wall-layer configurations, are solved through a finite difference scheme. Momentum equation is included for predicting pressure losses due to frictions and geometric irregularity. Exhaust fluid properties (transport and thermodynamic) are evaluated according to NASA or JANAF polynomial thermal data basis. The proposed tool allows the consideration of an arbitrary number of chemical species and reactions in the entire system. A novel semi-automatic approach was developed to handle catalytic reaction kinetics intuitively.

In order to meet the increasingly stringent emissions standard it is imperative that a two pronged approach is pursued for reduction of tailpipe emissions. In this regard emissions, and often the exhaust compositions, are needed to be controlled both at its source and then subsequently cleaned up at the exhaust system. In addition, an aftertreatment system often consists of an array of catalysts and its performance depends on the transient characteristics of the exhaust gas composition. To complicate the matter furthermore, relevant technologies are still evolving at a rapid pace. Consequently, an aftertreatment modeling approach should not only be system based but also offer a high level of configurability. Thus a system level approach that includes a model of an engine and vehicle may provide an efficient means to analyze system performance and examine relative effects of competing phenomena and technologies.

In order to reduce the cost of exhaust aftertreatment development, OEMs are increasingly relying on simulation of catalysts, traps and associated control systems. In this regards, for example, considerable progresses have been made on modeling diesel particulate filters. The work described in this paper was sought to provide a valid diesel particulate filter (DPF) model for coupling with engine/vehicle models under the same toolbox. A comprehensive two-level modeling approach, including a lumped parameter model and a detailed 1-D 3-layer-kinetics model, has been proposed for modeling wall-flow diesel particulate filters. Both are capable of modeling virtually all aspects of filter performance in terms of deep-bed filtration, particulate matter loading and filter regeneration.

The potential of fuel cells as an automotive power source is well recognized due to their high efficiency and zero tailpipe emissions. However, significant technical and economic hurdles need to be overcome in order to make this technology commercially viable. A proton-exchange membrane (PEM) fuel cell model has been developed to assess some of these technical issues. The fuel cell model can be operated in a standalone mode or it can be integrated with vehicle and fuel supply system models. A detailed thermal model of the fuel cell stack was used to identify significant design parameters that affect the performance of PEM fuel cell vehicles. The integrated vehicle model was used to explore the relative benefits of hybridization options.

An increasing emphasis is being placed in the vehicle development process on transient operation of engines and vehicles, and of engine/vehicle integration, because of their importance to fuel economy and emissions. Simulations play a large role in this process, complementing the more usual test-oriented hardware development process. This has fueled the development and continued evolution of advanced engine and powertrain simulation tools which can be utilized for this purpose. This paper describes a new tool developed for applications to transient engine and powertrain design and optimization. It contains a detailed engine simulation, specifically focused on transient engine processes, which includes detailed models of engine breathing (with turbocharging), combustion, emissions and thermal warm-up of components. Further, it contains a powertrain and vehicle dynamic simulation.

An S.I. combustion model has been developed for application in phenomenological engine simulations. The model is based on a turbulent flame concept, linked to an in-cylinder flow and turbulence calculation. The flame front is assumed to spread from the spark plug and propagate through the cylinder, while interacting with the combustion chamber geometry. The model predictions were compared to combustion rate measurements made in a single cylinder four valve passenger car engine. The data spanned a wide range of operating conditions, from an idle timing sweep, to part load EGR and mixture ratio sweeps, to a wide open throttle speed sweep. The results of the comparisons showed a generally good agreement. Some difficulties were encountered at idle, where cycle-to-cycle variability makes modeling difficult especially at early timing settings.

A model for oil consumption due to in-cylinder evaporation of oil in reciprocating engines, has been developed. The model is based on conservation of mass and energy on the surface of the oil film left on the cylinder by a piston ring pack, at the oil/gas interface, and also conservation of energy within the oil film and cylinder/coolant interface. The model is sensitive to in-cylinder conditions and is part of an integrated model of ring pack performance, which provides the geometry of the oil film left by the ring pack on the cylinder. Preliminary simulation results indicate that a relatively small but not insignificant fraction (2-5%) of the total oil consumption may be due to evaporation losses for a heavy duty diesel at the rated condition. The evaporation rate was shown to be sensitive to oil grade and upper cylinder temperature. Much of these losses occur during the non-firing half of the cycle.

Detailed heat transfer measurements were made in the combustion chamber of a Cummins single cylinder NH-engine in two configurations: cooled metal and ceramic-coated. The first configuration served as the baseline for a study of the effects of insulation and wall temperature on heat transfer. The second configuration had several in-cylinder components coated with 1.25 mm (0.050″) layer of zirconia plasma spray -- in particular, piston top, head firedeck and valves. The engine was operated over a matrix of operating points at four engine speeds and several load levels at each speed. The heat flux was measured by thin film thermocouple probes. The data showed that increasing the wall temperature by insulation reduced the heat flux. This reduction was seen both in the peak heat flux value as well as in the time-averaged heat flux. These trends were seen at all of the engine operating conditions.

A set of heat flux data was obtained in a Cummins single cylinder NH-engine coated with zirconia plasma spray. Data were acquired at two locations on the head, at several speeds and several load levels, using a thin film Pt-Pt/Rh thermocouple plated onto the zirconia coating. Careful attention was given to the probe design and to data reduction to assure high accuracy of the measurements. The data showed that the peak heat flux was consistently reduced by insulation and by the increasing wall temperature. The mean heat flux was also reduced. The results agree well with a previously developed flow-based heat transfer model. This indicates that the nature of the heat transfer process was unchanged by the increased wall temperature. Based on these results, the conclusion is drawn that insulation and increasing wall temperatures lead to a decrease in heat transfer and thus contribute positively to thermal efficiency.

An experimental study was conducted to measure the heat transfer in a direct injection 2.3 ℓ single cylinder diesel engine. The engine was operated at speeds ranging from 1000 to 2100 RPM and at a variety of loads. The heat transfer was measured using a total heat flux probe, operating on the principle of a thin film thermocouple, sensitive to both the convective and radiative heat flux. The probe was located in the head at two locations: opposite the piston bowl and opposite the piston crown (squish region). The measurements showed about twice as large peak heat flux in the bowl location than in the crown location for fired conditions, while under motoring conditions the relationship was reversed and the peak heat flux was slightly higher in the crown position. The experimental profiles of total heat flux were compared to the predictions obtained using a detailed thermodynamic cycle code, which incorporates highly resolved models of convective and radiative heat transfer.

An experimental study was conducted of the heat radiation in a single-cylinder direct injection 142 diesel engine. The engine was operated at speeds ranging from 1000 to 2100 RPM and a variety of loads. The radiation was measured using a specially designed fiber-optics probe operating on the two-color principle. The probe was located in the head at two different locations: in one location it faced the piston bowl and in the other it faced the piston crown. The data obtained from the probe was processed to deduce the apparent radiation temperature and soot volume concentration as a function of crank angle. The resultant profiles of radiation temperature and of the soot volume concentrations were compared with the predictions of a zonal heat radiation model imbedded in a detailed two-zone thermodynamic cycle code. The agreement between the model and the measurements was found to be good, both in trends and in magnitudes.

The use of an optical proximeter to determine dynamic top center in a motored engine is demonstrated. Design criteria are formulated and a data reduction procedure is presented. The method is shown to have an accuracy of Δθ = ± 0.1°. Variations in dynamic top center with engine speed that can be attributed to structural flexing and finite bearing clearances are shown to be less than ± 0.05°. It is also shown that the compression ratio during gas exchange is slightly larger than during compression-expansion. Other methods of finding top center are discussed and contrasted with optical proximetry. In this context a rational means of examining pressure records is presented and shown to be accurate to within Δθ=±0.3°.

A combustion bomb has been developed which allows simulation of diesel combustion without the need to heat the bomb to high temperatures. Simulation of the compression stroke is achieved by burning a lean precharge composed of acetylene, oxygen and nitrogen. By controlling the initial partial pressures of these constituents it is possible to burn them to a state with an oxygen concentration, temperature and pressure representative of conditions in a diesel engine at the start of fuel injection. Diesel fuel injected into these gases autoignites and burns in a manner typical of combustion in diesel engines. This paper describes the design and operation of such a bomb. Experimental results are presented to illustrate its salient features. Particular attention is devoted to various means of obtaining optical access to the flow and the advantages offered over rapid compression machines or heated bombs.