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In order to determine the area where knock occurs in a single cylinder engine, an acoustic methodology needs a minimum of four simultaneous pressure measurements in the combustion chamber. A specific cylinder head gasket integrating 12 pressure sensors has been developed and tested. The gasket is based on a bonded multilayer technology including high temperature piezoelectric cells, metallic and insulating sheets and printed circuit films. The total thickness is close to 1.25 mm (1/20 inch) and allows a straight forward substitution of the original gasket without modification. The sensors have large frequency bandwidth (typically 3-100 kHz) and withstand severe conditions (heat, combustion, pressure, vibrations, static pre-stress, electromagnetic fields and shocks). Signal processing adaptation of the dedicated exploitation software has brought good success for the single cylinder prototype, which remains operational after 100 hours of extreme conditions running (high knock).

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

Facing the stringent constraints on fuel consumption and pollutant emissions, the automotive manufacturers have to produce vehicles with an increasing number of complex systems working together. Numerical simulation for the system design, set-up and control strategies, helps to reduce the development cycle and the global cost. Existing simulation tools usually do not address, with a high level of details, the various physical domains involved in a vehicle powertrain. To overcome this challenge, IFP and IMAGINE, settled a partnership to develop detailed simulation tools dedicated to performance, consumption and emissions for conventional and hybrid vehicles [1]. These tools are integrated in a multi-domain simulation platform (AMESim®) where several levels of detail can be easily reached for each sub-element.

In the context of increasingly stringent pollution norms, reduced engine emissions are a great challenge for compressed ignition engines. After-treatment solutions are expensive and very complex to implement, while the NOx/PM trade-off is difficult to optimise for conventional Diesel engines. Therefore, in-cylinder pollutant production limitation by the HPC combustion mode (Highly Premixed Combustion) - including Homogeneous Charge Compression Ignition (HCCI) - represents one of the most promising ways for new generation of CI engine. For this combustion technology, control based on torque estimation is crucial: the objectives are to accurately control the cylinder-individual fuel injected mass and to adapt the fuel injection parameters to the in-cylinder conditions (fresh air and burned gas masses and temperature).

An experimental investigation into the structure and flame propagation characteristics of stratified and homogeneous combustion has been performed in an optically-accessible, direct-injection spark ignition (DISI) engine using OH planar laser-induced fluorescence (PLIF) imaging. Homogeneous and stratified operation was achieved by employing either early or late injection timing strategies during the intake or compression stroke respectively. Planar LIF OH images obtained revealed that for stratified operation, the 3D structure of the combustion zone is highly inhomogeneous and is predominantly due to high fuel concentration gradients which are formed as a result of local fuel mixture stratification. The images reveal a combustion structure which suggests that the flame propagation pathway is ultimately determined by the presence of these local fuel mixture inhomogeneities.

Three dimensional CFD tools are commonly used to simulate spray injection and combustion in DI Diesel engines. However typical computations are strongly mesh dependent. By now it is not possible to enhance grid resolution since it would violate the underlying assumptions for the Lagrangian liquid phase description. Besides, a full Eulerian approach with an adapted mesh is not practical at the moment mainly because of prohibitive computer requirements. Based on the Lagrangian-Eulerian approach, new approaches have been developed: the Coupled Lagrangian-Eulerian (CLE) model for the two-way coupling between the spray and the air flow and a new combustion model (CFM3Z) which allows a description of the fuel-oxidizer sub-grid mixing. The previously introduced CLE model consists in retaining vapor and momentum along parcel trajectories as long as the mesh is insufficient to resolve the steep gradients created by the spray.

A lumping model has been formulated to calculate the thermodynamic properties required for internal combustion engine multidimensional computations, including saturation pressure, latent heat of vaporization, liquid density, surface tension, viscosity, etc. This model consists firstly in reducing the analytical data to a single (i.e. pure) pseudo-component characterized by its molecular weight, critical pressure and temperature, and acentric factor. For a gasoline fuel, the required analytical data are those provided by gas chromatography. For a Diesel fuel, the required data are a true boiling point (TBP) distillation curve and the fuel density at a single temperature. This model provides a valuable tool for studying the effects of fuel physical properties upon the behavior of a vaporizing spray in a chamber, as well as upon direct injection gasoline and Diesel engines using the multidimensional (3D) KMB code.

Planar laser-induced fluorescence (LIF) imaging of formaldehyde (CH2O) and OH has been performed to investigate the homogeneous charge, compression ignition (HCCI) combustion process inside the piston bowl of an optically-accessible, direct injection Diesel-fueled HCCI engine. In particular, the effects of charge dilution and the adoption of single and split injection strategies on the two-stage HCCI combustion have been studied. Results obtained show that the level of exhaust gas recirculation (EGR) significantly affects the pre-combustion or so called cool flame phase during which formaldehyde is detected. The cool flame phasing as indicated by the formation of this intermediate species is unaffected by the EGR level however, auto-ignition timing which marks the start of main combustion is inevitably advanced following a reduction in EGR and this ultimately determines the formaldehyde lifetime and consequently the degree of homogeneity attained.

The influence of piston geometry on the in-cylinder mixture distribution and combustion process in an optically-accessible, direct injection HCCI Diesel engine has been investigated. A new, purpose-designed piston which allows optical access directly into the combustion chamber bowl permitted the application of a number of optical diagnostic techniques. Firstly, laser-induced exciplex fluorescence (LIEF) has been applied in order to characterize the fuel spray and vapor development within the piston bowl. Subsequently a detailed study of the auto-ignition and two-stage Diesel HCCI combustion process has been conducted by a combination of direct chemiluminescence imaging, laser-induced fluorescence (LIF) of the intermediate species formaldehyde (CH2O) which is present during the cool flame and LIF of the OH radical later present in the reaction and burned gas zones at higher temperature.

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.

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 been exploring development avenues 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 FSH (Fonds de Soutien aux Hydrocarbures), IFP, PSA-Peugeot-Citroën, Renault and Renault VI (Véhicules Industriels), has been built to study this point. It is a four years programme with different steps which will focus on new engine technologies: some of them are going to be marketed very soon (gasoline direct injection car engine, and diesel common rail injection car and truck engines) to anticipate the Euro 3 (2000) and the Euro 4 (2005) emissions specifications. The original work reported here is part of this research.

The purpose of the ELEVATE (European Low Emission V4 Automotive Two-stroke Engine) industrial research project is to develop a small, compact, light weight, high torque and highly efficient clean gasoline 2-stroke engine of 120 kW which could industrially replace the relatively big existing automotive spark ignition or diesel 4-stroke engine used in the top of the mid size or in the large size vehicles, including the minivan vehicles used for multi people and family transportation. This new gasoline direct injection engine concept is based on the combined implementation on a 4-stroke bottom end of several 2-stroke engine innovative technologies such as the IAPAC compressed air assisted direct fuel injection, the CAI (Controlled Auto-Ignition) combustion process, the D2SC (Dual Delivery Screw SuperCharger) for both low pressure engine scavenging and higher pressure IAPAC air assisted DI and the ETV (Exhaust charge Trapping Valve).

A methodology which uses simultaneously 3D calculations and advanced experimental tools has been developed in order to characterize air-fuel mixing and combustion of gasoline direct injection engines at every stage of development. The analysis of Mitsubishi GDI engine has been carried out in order to validate this approach. The experimental tools used in this analysis underline the great cycle-to-cycle variability and show that the air-fuel ratio variations at spark plug correlate closely with the fluctuations of combustion starting and development. Despite this variability, average measurements are reproducible and in good agreement with 3D computational results obtained with KIVA-MB code. The common use of both kinds of tools allows to get a very fine understanding of Mitsubishi wall-guided concept.

A database of information concerning the spray development and pollutant formation in common-rail, direct-injection Diesel engine is constructed using a transparent model Diesel engine. Spray development is investigated using optical diagnostics: Mie scattering and Laser Induced Exciplex Fluorescence (LIEF) make possible qualitative visualization of liquid and vapor phases. The injection pressure/nozzle hole diameter is found to be the most important parameter (in the parameter range used for the study): it reduces the liquid penetration length and improves the mixing of vapor fuel. Direct imaging of combustion development shows the influence of different engine parameters on flame location. Comparison with measured vapor distributions shows the effect of thermal expansion on the vapor plume before any light from combustion is visible. Soot formation is investigated using Laser Induced Incandescence imaging.

The reduction of particulate emissions from Diesel engines is a key issue to meet future emission standards. Particulate traps represent an attractive solution to the problem of this source of pollution. However, they have the disadvantage of requiring periodic and safe regeneration to release exhaust back pressure and to recover filtration efficiency. Natural regeneration of the particulate filter may occur. Nevertheless, with light-duty vehicles and their low level of exhaust gas temperature, it may be necessary to facilitate or force the regeneration. The objective of this work is to give an overview of the possibilities offered by the engine management system to increase significantly exhaust gas temperatures. Thus, different engine tunes, through injection timing, boost pressure or EGR rate, may be sufficient to ensure safe regeneration of the trap.

The short time available for injection and mixing in high-speed engines requires an accurate modeling of the fuel related processes to obtain a valuable in-cylinder charge description, and then a good combustion performance prediction. An advanced version of the KMB code of IFP has been used to compute a racing engine. It includes a fitted on experiments spray model, a comprehensive wall-film model, the AKTIM ignition and ECFM combustion models. A major difficulty was the necessity to compute numerous cycles before reaching a cycle-independent solution. A procedure has been defined to minimize calculation time. Another difficulty was the high concentration of liquid in some zones, which requested a careful meshing. Effects such as the influence of the strong acoustic waves on the spray dynamic, the wall wetting effects on the engine time response, injector position on fuel distribution in the cylinder, charge homogeneity on the combustion process have been investigated.