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Transported probability density function (PDF) methods are currently being pursued as a viable approach to model the effects of turbulent mixing and mixture stratification, especially for new alternative combustion modes as for example Homogeneous Charge Compression ignition (HCCI) which is one of the advanced low temperature combustion (LTC) concepts. Recently, they have been applied to simple engine configurations to demonstrate the importance of accurate accounting for turbulence/chemistry interactions. PDF methods can explicitly account for the turbulent fluctuations in species composition and temperature relative to mean value. The choice of the mixing model is an important aspect of PDF approach. Different mixing models can be found in the literature, the most popular is the IEM model (Interaction by Exchange with the Mean). This model is very similar to the LMSE model (Linear Mean Square Estimation).

In an industrial context, close to the start of production and development of Engine Control Unit (ECU) systems, it is necessary to validate the complete dataset of the application and thus, to run software tests on a real ECU which is connected to a closed loop HIL Test bench, In the field of application for the simulation of dataset and the reduction of real vehicle tests, it is required to simulate an engine behaviour in terms of mixture mass and energy flow rate, temperature and pressure. The aim of this work is to reproduce this engine behaviour with a focus on combustion process and component simulation models, Oxidation Catalyst (OxiCat) and Diesel Particulate Filter (DPF). A model has been developed with the help of experimental data extracted from an Original Equipment Manufacturer (OEM) engine project.

Transient operation in port-injected engines often results in long lasting air-fuel ratio excursions. These excursions lead to high levels of pollutant emissions even in three-way catalyst equipped vehicles. The reduction of these excursions can be achieved by controlling fuel injection, but the exact amount of fuel to be injected is dependant on air flow and deposited fuel dynamics. This paper describes a complete model of the intake port, taking into account physical evolutions of three phases in a bidimensional geometry. Back-flow of hot burned gases, droplet trajectories, droplet evaporation, deposited fuel film flow, deposited fuel film evaporation, and air flow are taken into account. The model is used to predict air-fuel ratio excursions during engine transients. Results are compared to measurements made on a real four-cylinder engine with an oxygen sensor on the exhaust port of one cylinder, for several operating conditions.

Mainly due to environmental regulation, future Engine Control Unit (ECU) will be equipped with in-cylinder pressure sensors. The introduction of this innovative solution has increased the number of involved variables, requiring an unceasing improvement in the modeling approaches and in the computational capabilities of Engine Control Unit (ECU). Hardware in the Loop (HIL) test system therefore has to provide in-cylinder pressure in real time from an adequate model. This paper describes a synthesis of our study targeted to the development of in-cylinder crank angle combustion model excluding look up tables, dedicated to HIL test bench. The main objective of the present paper is a comprehensive analysis of a reduced combustion model, applied to a direct injection Diesel engine at varying engine operating range, including single injection and multi injection strategies.

This paper presents a DI diesel engine combustion model based on double Wiebe equations approach. The aim of this work is to build a combustion model suitable for Hardware-in-the-Loop (HiL) simulations, and thus to be able to run in real-time applications. First, an ignition model is presented and correlated function of engine operating conditions. Then the combustion model parameters have been calibrated with a curve fitting technique with test bench experimental results. The calibration and validation process have been realized first on Matlab. Then the combustion model was coded in S-functions Simulink blocks suitable for HiL implementation. Offline test results for single injection cases with high engine speed (≻4000 rpm) are presented in this paper.

The potential of internal EGR (iEGR) and external EGR (eEGR) in reducing the engine-out NOx emissions in a heavy-duty diesel engine has been investigated by means of a refined 1D fluid-dynamic engine model developed in the GT-Power environment. The engine is equipped with Variable Valve Actuation (VVA) and Variable Geometry Turbocharger (VGT) systems. The activity was carried out in the frame of the CORE Collaborative Project of the European Community, VII FP. The engine model integrates an innovative 0D predictive combustion algorithm for the simulation of the HRR (heat release rate) based on the accumulated fuel mass approach and a multi-zone thermodynamic model for the simulation of the in-cylinder temperatures. NOx emissions are calculated by means of the Zeldovich thermal and prompt mechanisms.

The current trend of downsizing used in gasoline engines, while reducing fuel consumption and CO2 emissions, imposes severe thermal loads inside the combustion chamber. These critical thermodynamic conditions lead to the possible auto-ignition (AI) of fresh gases hot-spots around Top-Dead-Center (TDC). At this very moment where the surface to volume ratio is high, wall heat transfer influences the temperature field inside the combustion chamber. The use of a realistic wall temperature distribution becomes important in the case of a downsized engine where fresh gases hot spots found near high temperature walls can initiate auto-ignition. This paper presents a comprehensive numerical methodology for an accurately prediction of thermodynamic conditions inside the combustion chamber based on Conjugate Heat Transfer (CHT).

Natural gas is a promising alternative fuel for internal combustion engine application due to its low carbon content and high knock resistance. Performance of natural gas engines is further improved if direct injection, high turbocharger boost level, and variable valve actuation (VVA) are adopted. Also, relevant efficiency benefits can be obtained through downsizing. However, mixture quality resulting from direct gas injection has proven to be problematic. This work aims at developing a mono-fuel small-displacement turbocharged compressed natural gas engine with side-mounted direct injector and advanced VVA system. An injector configuration was designed in order to enhance the overall engine tumble and thus overcome low penetration.

CNG is one of the most promising alternate fuels for passenger car applications. CNG is affordable, is available worldwide and has good intrinsic properties including high knock resistance and low carbon content. Usually, CNG engines are developed by integrating CNG injectors in the intake manifold of a baseline gasoline engine, thereby remaining gasoline compliant. However, this does not lead to a bi-fuel engine but instead to a compromised solution for both Gasoline and CNG operation. The aim of the study was to evaluate the potential of a direct injection spark ignition engine derived from a diesel engine core and dedicated to CNG combustion. The main modification was the new design of the cylinder head and the piston crown to optimize the combustion velocity thanks to a high tumble level and good mixing. This work was done through computations. First, a 3D model was developed for the CFD simulation of CNG direct injection.

The introduction of alternative fuels is crucial to limit greenhouse gases. CNG is regarded as one of the most promising clean fuels given its worldwide availability, its low price and its intrinsic properties (high knocking resistance, low carbon content...). One way to optimize dedicated natural gas engines is to improve the CNG slow burning velocity compared to gasoline fuel and allow lean burn combustion mode. Besides optimization of the combustion chamber design, hydrogen addition to CNG is a promising solution to boost the combustion thanks to its fast burning rate, its wide flammability limits and its low quenching gap. This paper presents an investigation of different methane/hydrogen blends between 0% and 40 vol. % hydrogen ratio for three different combustion modes: stoichiometric, lean-burn and stoichiometric with EGR.

Engine knock is an important phenomenon that needs consideration in the development of gasoline fueled engines. In our days, this development is supported by the use of numerical simulation tools to further understand and subsequently predict in-cylinder processes. In this work, a model tool chain based on detailed chemical and physical models is proposed to predict the auto-ignition behavior of fuels with different octane ratings and to evaluate the transition from harmless auto-ignitive deflagration to knocking combustion. In our method, the auto-ignition and emissions are calculated based on a new reaction scheme for mixtures of iso-octane, n-heptane, toluene and ethanol (Ethanol consisting Toluene Reference Fuel, ETRF). The reaction scheme is validated for a wide range of mixtures and every desired mixture of the four fuel components can be applied in the engine simulation.

One of the most important safety issues for automotive engineering is to avoid any fire due to the ignition of flammable liquids, which may result from leaks. Fire risk is a combination of hot temperature, fast vaporisation and accumulation of vapor in a cavity. In IC engines, potentially flammable liquids are fuel and oil. To guarantee safety, flammable liquids must not come into contact with hot parts of the engine. Consequently, shields are designed to guide the flow path of possible leakages and to take any flammable liquid out of the hot areas. Simulation is a great help to optimize the shape of the shield by investigating a large number of possible leakages rapidly. Recent breakthroughs in numerical methods make it possible to apply simulations to industrial design concepts. The employed approach is based on the Lagrangian Smoothed Particle Hydrodynamics (SPH) method.

The present paper is concerned with part of the work performed by Renault, IFPEN and Politecnico di Torino within a research project founded by the European Commission. The project has been focused on the development of a dedicated CNG engine featuring a 25% decrease in fuel consumption with respect to an equivalent Diesel engine with the same performance targets. To that end, different technologies were implemented and optimized in the engine, namely, direct injection, variable valve timing, LP EGR with advanced turbocharging, and diluted combustion. With specific reference to diluted combustion, it is rather well established for gasoline engines whereas it still poses several critical issues for CNG ones, mainly due to the lower exhaust temperatures. Moreover, dilution is accompanied by a decrease in the laminar burning speed of the unburned mixture and this generally leads to a detriment in combustion efficiency and stability.

Sustainable mobility has become a major issue for internal combustion engines and has led to increasing research efforts in the field of alternative fuels, such as bio-fuel, CNG and hydrogen addition, as well as into engine design and control optimization. To that end, a thorough control of the air-to-fuel ratio appears to be mandatory in SI engine in order to meet the even more stringent thresholds set by the current regulations. The accuracy of the air/fuel mixture highly depends on the injection system dynamic behavior and to its coupling to the engine fluid-dynamic. Thus, a sound investigation into the mixing process can only be achieved provided that a proper analysis of the injection rail and of the injectors is carried out. The present paper carries out a numerical investigation into the fluid dynamic behavior of a commercial CNG injection system by means of a 0D-1D code.

Homogeneous charge compression ignition (HCCI) is one of the alternatives to reduce significantly diesel engine emissions for the future emissions regulations. This new alternative combustion process is mainly controlled by chemical kinetics, unlike conventional combustion in internal combustion engines. To satisfy the different modes of operation, the tuning of HCCI engines requires a large number of tests which are time-consuming and very expensive. To reduce the number of tests, a model with a very short computational time to simulate the engine in the whole operating range is needed; therefore the goal of this study is to provide the engine manufacturers with a simple physical combustion model to assist engine tuning and engine management system optimization, with the aim of predicting in-cylinder pressure evolutions and mean effective pressure (IMEP).

In order to elaborate accurate injection-control strategies aimed at limiting pollutant emissions resulting from transient S.I. engines operation, it is necessary to gain better understanding of the mixture formation. In this paper, we present the first stage of a software whose purpose is to model in a phenomenological way an S.I. engine cycle in order to study mixture formation during transient operation. With respect to crank angle, it computes pressures and flow-rates throughout the engine (from the throttle to the exhaust port), the description of liquid and vapor fuel in the intake ports and the instantaneous equivalence ratio of the mixture entering the cylinders. It is shown the non homogeneity of the intake port and in-cylinder mixture during the cycle, the importance of the liquid fuel film flow and the influence of the flow rates and pressures calculations on the fuel behavior.

Direct injection (DI) of natural gas (NG) at high pressure conditions has emerged as a high-potential strategy for improving SI engine performance. Besides, DI allows an increase in the fuel economy, due to the possibility of a significant engine dethrottling at partial load. The high-pressure gas injection can also increase the turbulence level of mixture and thus the overall fuel-air mixing. Since direct NG injection is an emerging technology, there is a lack of experience on the optimum configuration of the injection system and the associated combustion chamber design. In the last few years, some numerical investigations of gas injection have been made, mainly oriented at the development of reliable numerical investigation tools. The present paper is concerned with the development and application of a numerical Star-CD based model for the investigation of the direct NG injection process from a poppet-valve injector into a bowl-piston engine combustion chamber.

Ignition delay time is key to any hydrocarbon combustion process. In that sense, this parameter has to be known accurately, and especially for internal combustion engine applications. Combustion timing is one of the most important factors influencing overall engine performances like power output, combustion efficiency, emissions, in-cylinder peak pressure, etc. In the case of low temperature combustion (LTC) mode (e.g. HCCI mode), this parameter is controlled by chemical kinetics. In this paper, an ignition delay time model including 7 direct reactions and 13 species coupled with a temperature criterion is described. This mechanism has been obtained from the previous 26-step n-heptane reduced mechanism, focusing on the low temperature region which is the most important phase during the two stage combustion process. The complete model works with 7 reactions until the critical temperature is reached, leading to the detection of the ignition delay time value.

The homogeneous charge compression ignition (HCCI) is one of the alternative to reduce significantly engine emissions for the future regulations. The combustion process in HCCI engines does not involve flame propagation or flame diffusion as in conventional internal combustion engines. Many studies have confirmed that during this mode the combustion process is mainly controlled by chemical kinetics. However, a coupled CFD and detailed chemistry simulation requires substantial memory and CPU time which may be very difficult with current computer capabilities. Thus a reduced mechanism is required to simulate the engine cycle during this operating mode to achieve more accurate analysis. In this study reduced chemistry was used with an engine CFD code combustion (Star-CD/Kinetics) to study combustion process in homogeneous charge compression ignition (HCCI) engines.

This paper presents the results of part of the research activity carried out by the Politecnico di Torino and AVL List GmbH as part of the European Community InGAS Collaborative Project. The work was aimed at developing a combustion system for a mono-fuel turbocharged CNG engine, with specific focus on performance, fuel economy and emissions. A numerical and experimental analysis of the jet development and mixture formation in an optically accessible, single cylinder engine is presented in the paper. The experimental investigations were performed at the AVL laboratories by means of the planar laser-induced fluorescence technique, and revealed a cycle-to-cycle jet shape variability that depended, amongst others, on the injector characteristics and in-cylinder backpressure. Moreover, the mixing mechanism had to be optimized over a wide range of operating conditions, under both stratified lean and homogeneous stoichiometric modes.