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Quantitative fuel concentration visualizations are carried out to study the mixing process between fuel and air in Direct Injection (DI) Diesel like conditions, and generate high quality data for the validation of mixing models. In order to avoid the particular complication connected with fuel droplets, a gaseous fuel jet is investigated. Measurements are performed in a high-pressure chamber that can provide conditions similar to those in a diesel engine. A gas injection system able to perform injections in a high-pressure chamber with a good control of the boundary conditions is chosen and characterized. Mass flow rates typical of DI Diesel injection are reproduced. A Laser Induced Fluorescence technique requiring the mixing at high pressure of the fluorescent tracer, biacetyl, with the gaseous fuel, methane, is developed. This experimental technique is able to provide quantitative measurement of fuel concentration in high-pressure jets.

Compressed natural gas (CNG) is considered as one of the most promising alternative fuels for transportation due to its ability to reduce greenhouse gas emissions (CO2, in particular) and its abundance. An earlier study from IFP has shown that CNG has a considerable potential when used as a fuel for a dedicated downsized turbo-charged SI engine on a small urban vehicle. To take further advantage of CNG assets, this approach can be profitably extended by adding a small secondary (electrical) power source to the CNG engine, thus hybridizing the powertrain. This is precisely the focus of the new IFP project, VEHGAN, which aims to develop a mild-hybrid CNG prototype vehicle based on a MCC smart car equipped with a reversible starter-alternator and ultra-capacitors (Valeo Starter Alternator Reversible System, StARS).

Soot models applied to Diesel combustion can be grouped into two classes, one based on the flamelet concept and the other based on the homogeneous reactor concept. The first assumes that the laminar diffusion flame structure of the reaction zone, in the mixture fraction space, is preserved while convected and strained by the turbulent flow. The second assumes that the properties of the reaction zone are locally homogeneous. Thus the aerodynamic and chemical reaction interactions are modeled with opposing assumptions: the first assumes fast chemistry, the second fast mixing. In this work, we first compare results obtained with a flamelet library approach to those with a homogeneous reactor approach. Recognizing that both types of models apply in different regions of Diesel combustion, we then propose a new approach for soot modeling in which they are coupled.

Currently, the development of higher specific output and higher efficiency S.I. engines requires better control and knowledge of knock mechanisms. As it is not easily possible to instrument an engine to determine the beginning of fuel auto-ignition, knock modeling by means of 3D CFD simulation, can be a powerful tool to understand and try to avoid this phenomenon [1, 2, 3]. The objectives of the work described in this paper are to develop and validate a simple model of auto-ignition. This model, developed at IFP, is implemented in the 3D CFD code KMB [4, 5]. It is based on an AnB model [6, 7] which creates a ‘precursor’ species transported with the flow in the combustion chamber. When its concentration reaches a limiting value, the auto-ignition phenomenon occurs.

Recent developments on highly downsized spark ignition engines have been focused on knocking behaviour improvement and the most advanced technologies combination can face up to 2.5 MPa IMEP while maintaining acceptable fuel consumption. Unfortunately, knocking is not the only limit that strongly downsized engines have to confront. The improvement of low-end torque is limited by another abnormal combustion which appears as a random pre-ignition. This violent phenomenon which emits a sharp metallic noise is unacceptable even on modern supercharged gasoline engines because of the great pressure rise that it causes in the cylinder (up to 20 MPa). The phases of this abnormal combustion have been analysed and a global mechanism has been identified consisting of a local ignition before the spark, followed by a propagating phase and ended by a massive auto-ignition. This last step finally causes a steep pressure rise and pressure oscillations.

Facing the CO2 emission reduction challenge, the combination of downsizing and turbocharging appears as one of the most promising solution for the development of high efficiency gasoline engines. In this context, as knock resistance is a major issue, limiting the performances of turbocharged downsized gasoline engines, fuel properties are more than ever key parameters to achieve high performances and low fuel consumption's levels. This paper presents a combustion study carried out into the GSM consortium of fuel quality effects on the performances of a downsized turbocharged Direct Injection SI engine. The formulation of two adapted fuel matrix has allowed to separate and evaluate the impacts of three major fuel properties: Research Octane Number (RON), Motor Octane Number (MON) and Latent Heat of Vaporization (LHV). Engine tests were performed on a single cylinder engine at steady state operating condition.

Modelling small and large scale fluctuations of fuel distribution is of high interest for stratified direct injection spark ignition (DISI) engines. Homogeneous combustion models need to be extended or replaced in order to account for these fluctuations. They are presently neglected in most engine simulations. Effects of mean fuel/air equivalence ratio gradient have been recently included in previous homogeneous mixture approaches. To account for local fluctuations of mixture composition, the new model ECFM-Z has been developed on the basis of recent Direct Numerical Simulation results and Coherent Flame Surface modelling. The model has been implemented in a CFD code (KMB) The influence of mixture fraction is integrated in the Extended Coherent Flame Surface combustion model. The model is based on a conditional approach. Unburnt hydrocarbons produced by lean flame local extinctions are taken into account.

Among the existing concepts to help improve the efficiency of spark ignition engines on low load operating points, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions at part load without major modifications of the engine design. The CAI™ concept is founded on the auto-ignition of a highly diluted gasoline-based mixture in order to reach high indicated efficiency and low pollutant emissions through a low temperature combustion. Previous research works have demonstrated that the valve strategy is an efficient way to control the CAI™ combustion mode. Not only the valve strategy has an impact on the amount of trapped burnt gases and their temperature, but also different valve strategies can lead to equivalent mean in-cylinder conditions but clearly differentiated combustion timing or location. This is thought to be the consequence of local mixture variations acting in turn on the chemical kinetics.

Among the existing concepts that help to improve the efficiency of spark ignition engines at part load, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions without major modifications of the engine design. The CAI™ concept is based on the auto-ignition of a fuel mixture highly diluted with burnt gases in order to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. In a 4-stroke engine, large amounts of burnt gases can be trapped in the cylinder by re-breathing them through the exhaust ports during the intake stroke using a 2-step exhaust valve-lift profile. The interaction between the intake and exhaust flows during the intake stroke was identified as a key parameter to control the subsequent combustion in a CAI™ PFI engine. Consequently, the intake valve-lift profile as well as the exhaust re-opening profile can potentially be used as control parameters for this combustion mode.

Among the existing concepts that help to improve the efficiency of spark ignition engines at part load, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions without major modifications of the engine design. The CAI™ concept is based on the auto-ignition of a fuel mixture highly diluted with burnt gases in order to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. Large amounts of burnt gases can be trapped in the cylinder by re-breathing them through the exhaust ports during the intake stroke. For that, a 2-step exhaust valve-lift profile is used. The interaction between the intake and exhaust flows during the intake stroke was identified as a key parameter to control the subsequent combustion in a CAI™ port fuel injected (PFI) engine.

Due to increasingly stringent regulations, reduction of pollutant emissions and consumption are currently two major goals of the car industry. One way to reach these objectives is to enhance the management of the engine in order to optimize the whole combustion process. This requires the development of complex control strategies for the air and the fuel paths, and for the combustion process. In this context, engine 0D modelling emerges as a pertinent tool for investigating and validating such strategies. Indeed, it represents a useful complement to test bench campaigns, on the condition that these 0D models are accurate enough and manage to run quite fast, eventually in real time. This paper presents the different steps of the design of a high frequency 0D simulator of a downsized turbocharged Port Fuel Injector (PFI) engine, compatible with real time constraints.

In the whole engine development process, 0D/1D simulation has become a powerful tool, from conception to final calibration. Within the context of control strategy design, a turbocharged spark ignition (SI) engine with variable camshaft timing has been modelled on the AMESim platform. This paper presents the different models and the methodology used to design, calibrate and validate the simulator. The validated engine model is then used for engine control purposes related to downsizing concept. Indeed, the presented control strategy acts on the in-cylinder trapped mass, the in-cylinder burnt gas fraction and the air scavenging from the intake to the exhaust. Consequently, it permits to reduce not only the fuel consumption and pollutant emissions but also to improve the transient response of the turbocharger

Air quality improvement, especially in urban areas, is one of the major concerns for the coming years. For this reason, car manufacturers, equipment manufacturers and refiners have explored development issues to comply with increasingly severe anti-pollution requirements. In such a context, the identification of the most promising improvement options is essential. A research program, carried out by IFP (Institut Français du Pétrole), and supported by the French Ministry of Industry, IFP, PSA-Peugeot-Citroën, Renault and RVI (Renault Véhicules Industriels), has been built to study this point. It is based on a three years program with different steps focused on new engine technologies which will be available in the next 20 years in order to answer to more and more severe pollutant and CO2 emission regulations. This program is divided into three main parts: the first one for Diesel car engines, the second for Diesel truck engines and the third for spark ignition engines.

Among the existing concepts that help to improve the efficiency of spark-ignition engines at part load, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions. This combustion concept is based on the auto-ignition of an air-fuel-mixture highly diluted with hot burnt gases to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. To minimize the costs of conversion of a standard spark-ignition engine into a CAI engine, the present study is restricted to a Port Fuel Injection engine with a cam-profile switching system and a cam phaser on both intake and exhaust sides. In a 4-stroke engine, a large amount of burnt gases can be trapped in the cylinder via early closure of the exhaust valves. This so-called Negative Valve Overlap (NVO) strategy has a key parameter to control the amount of trapped burnt gases and consequently the combustion: the exhaust valve-lift profile.

Lean-burn combustion in SI engines can significantly reduce fuel consumption but NOx reduction becomes challenging because classic three-way catalyst (TWC) is no more efficient. Urea-SCR is then an interesting alternative solution because of its high NOx conversion efficiency without any additional fuel consumption. The coupling between two SI lean-burn engines (stratified and homogeneous combustion) and a urea-SCR catalyst was simulated on the NEDC cycle. Simulation results showed that the SCR efficiency would comply with the limits required by future Euro 5/6 regulations. Associated urea solution consumptions were estimated thanks to a simplified model. Finally, a comparison with a Diesel application was also made. It showed that the required amount of reducing agent remained significantly higher for SI lean-burn engines than for Diesel engine.

In the context of modern engine control, one important variable is the individual Air Fuel Ratio (AFR) which is a good representation of the produced torque. It results from various inputs such as injected quantities, boost pressure, and the exhaust gas recirculation (EGR) rate. Further, for forthcoming HCCI engines and regeneration filters (Particulate filters, DeNOx), even slight AFR unbalance between the cylinders can have dramatic consequences and induce important noise, possible stall and higher emissions. Classically, in Spark Ignition engine, overall AFR is directly controlled with the injection system. In this approach, all cylinders share the same closed-loop input signal based on the single λ-sensor (normalized Fuel-Air Ratio measurement, it can be rewritten with AFR as they have the same injection set-point.

In order to address the CO₂ emissions issue and to diversify the energy for transportation, CNG (Compressed Natural Gas) is considered as one of the most promising alternative fuels given its high octane number. However, gaseous injection decreases volumetric efficiency, impacting directly the maximal torque through a reduction of the cylinder fill-up. To overcome this drawback, both independent natural gas and gasoline indirect injection systems with dedicated engine control were fitted on a RENAULT 2.0L turbocharged SI (Spark Ignition) engine and were adapted for simultaneous operation. The main objective of this innovative combination of gas and liquid fuel injections is to increase the volumetric efficiency without losing the high knocking resistance of methane.