Search Results

This paper presents an innovative methodology and the corresponding results of a study whose goal is to identify the main links between in-cylinder charge motion and the development of combustion without taking into consideration how to create this charge motion (shape of the intake ducts, valve timing, etc …). During this study a specific methodology was developed and used. It is based on the calculation of a “3D numerical test bench” matrix planned following the Design Of Experiments method. Many aerodynamic configurations obtained by combining the three main aerodynamic motions with several different intensities (tumble, cross-tumble or swirl) at the intake valve closing were calculated.

The target of substantial CO₂ reductions in the spirit of the Kyoto Protocol as well as higher engine efficiency requirements has increased research efforts into hybridization of passenger cars. In the frame of this hybridization, there is a real need to develop small Internal Combustion Engines (ICE) with high power density. The two-stroke cycle can be a solution to reach these goals, allowing reductions of engine displacement, size and weight while maintaining good NVH, power and consumption levels. Reducing the number of cylinders, could also help reduce engine cost. Taking advantage of a strong interaction between the design office, 0D system simulations and 3D CFD computations, a specific methodology was set up in order to define a first optimized version of a two-stroke uniflow diesel engine. The main geometrical specifications (displacement, architecture) were chosen at the beginning of the study based on a bibliographic pre-study and the power target in terms.

Reducing NOx tailpipe emissions is one of the major challenges when developing automotive Diesel engines which must simultaneously face stricter emission norms and reduce their fuel consumption/CO2 emission. In fact, the engine control system has to manage at the same time the multiple advanced combustion technologies such as high EGR rates, new injection strategies, complex after-treatment devices and sophisticated turbocharging systems implemented in recent diesel engines. In order to limit both the cost and duration of engine control system development, a virtual engine simulator has been developed in the last few years. The platform of this simulator is based on a 0D/1D approach, chosen for its low computational time. The existing simulation tools lead to satisfactory results concerning the combustion phase as well as the air supply system. In this context, the current paper describes the development of a new NOx emission model which is coupled with the combustion model.

Child dummies used in certification dynamic tests have not been improved since their marketing and their approval as European regulation dummies. Their main shortcoming lies in a too high and therefore unrealistic stiffness of the torso front part. The paper addresses a study carried out in the aim of solving this problem. It includes two parts: in a first section, the changes brought to the dummy torso and intended to improve its biofidelity and to reduce stiffness drastically are described. In order to reach such an objective, the lower part of the upper torso was remodelled; the pelvis profile was redefined and the geometrical and mechanical characteristics of the foam used for the abdominal insert were changed. The results obtained using two transducers installed in the abdominal section are then presented. The measurement principle of the first transducer consists in a pressure measurement, and the principle of the second one in a load measurement.

This paper presents a new 0D phenomenological approach to predict the combustion process in diesel engines operated under various running conditions. The aim of this work is to develop a physical approach in order to improve the prediction of in-cylinder pressure and heat release. The main contribution of this study is the modeling of the premixed part of the diesel combustion with a further extension of the model for multi-injection strategies. In phenomenological diesel combustion models, the premixed combustion phase is usually modeled by the propagation of a turbulent flame front. However, experimental studies have shown that this phase of diesel combustion is actually a rapid combustion of part of the fuel injected and mixed with the surrounding gas. This mixture burns quasi instantaneously when favorable thermodynamic conditions are locally reached. A chemical process then controls this combustion.

The purpose of the European « SPACE LIGHT » (Whole SPACE combustion for LIGHT duty diesel vehicles) 3-year project launched in 2001 is to research and develop an innovative Homogeneous internal mixture Charged Compression Ignition (HCCI) for passenger cars diesel engine where the combustion process can take place simultaneously in the whole SPACE of the combustion chamber while providing almost no NOx and particulates emissions. This paper presents the whole project with the main R&D tasks necessary to comply with the industrial and technical objectives of the project. The research approach adopted is briefly described. It is then followed by a detailed description of the most recent progress achieved during the tasks recently undertaken. The methodology adopted starts from the research study of the in-cylinder combustion specifications necessary to achieve HCCI combustion from experimental single cylinder engines testing in premixed charged conditions.

For many years, bearing suppliers have been using the specific pressure to evaluate the fatigue risk of conrod bearings. However, modern engines have made the bearing more sensitive to various phenomena such as the thermal expansion or the elasticity of the conrod housing. These effects modify the stresses in the bearing layers and consequently fatigue risk. In this paper, we propose a new way to determine the bearing fatigue resistance. To achieve that, we analyze the elastic and plastic behavior of the bearing along the engine life. We detail and provide the analytical relationships which determine stresses in the overlay and in the substrate of the bearing in order to analyze their fatigue resistance. Various physical loads are taken into account such as the thermal load, the hydrodynamic pressure field, the fitting load, the free spread load. A good knowledge of the relationships between those physical phenomena helps to understand the mechanical behavior of the bearing.

Engine downsizing is potentially one of the most effective strategies being explored to improve fuel economy. A main problem of downsizing using a turbocharger is the small range of stable functioning of the turbocharger centrifugal compressor at high boost pressures, and hence the measurement of the performance maps of both compressor and turbine. Automotive manufacturers use mainly numerical simulations for internal combustion engines simulations, hence the need of an accurate extrapolation model to get a complete turbine performance map. These complete maps are then used for internal combustion engines calibration. Automotive manufacturers use commercial softwares to extrapolate the turbine narrow performance maps, both mass flow characteristics and the efficiency curve.

Due to its harmful effect on both human health and environment, soot emission is considered as one of the most important diesel engine pollutants. In the last decades, the industrial engine manufacturers have been able to strongly reduce its engine-out value by many different techniques, in order to respect the stricter emission norms. Simulation modeling has played and continues to play a key role for this purpose in the engine control system development. In this context, this paper proposes a new soot emission model for a direct injection diesel engine. This soot model is based on a zero-dimensional semi-physical approach coupled with a crank-angle resolved combustion model and a thermodynamic calculation of the burned gas products temperature. Furthermore, a multi linear regression model has been used to estimate the soot emissions as function of significant physical combustion parameters.

An innovative alternative to overcome the load limits of the early injection highly premixed combustion concept consists of taking advantage of the intrinsic characteristics of two-stroke engines, since they can attain the full load torque of a four-stroke engine as the addition of two medium load cycles, where the implementation of this combustion concept could be promising. In this frame, the main objective of this investigation focuses on evaluating the potential of the early injection HPC concept using a conventional diesel fuel combined with a two-stroke poppet valves engine architecture for pollutant control, while keeping a competitive engine efficiency. On a first stage, the HPC concept was implemented at low engine load, where the concept is expected to provide the best results, by advancing the start of injection towards the compression stroke and it was confirmed how it is possible to reduce NOX and soot emissions, but increasing HC and CO emissions.

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.

This paper proposes a method to detect an intake manifold leakage for a Diesel engine with a dual loop EGR system. The intake manifold leak has a strong impact on the engine performances by changing the intake manifold burned gas ratio. This fault is analyzed according to the control structure used and also according to the EGR operating mode. The paper proposes a diagnosis algorithm to detect the intake manifold leak in sequential or simultaneous use of the two EGR paths. The sensors considered are the mass air flow meter, the intake manifold pressure sensor, the exhaust equivalence ratio sensor and the differential pressure sensor (across the HP EGR valve). The diagnosis is based on a criteria that uses the redundancy between these sensors and air system models or estimators. The diagnosis threshold depends on the engine operating conditions as well as the sensor or model dispersions.

This paper introduces a research work on the air loop system for a downsized two-stroke two-cylinder diesel engine conducted in framework of the European project dealing with the POWERtrain for Future Light-duty vehicles - POWERFUL. The main objective was to determine requirements on the air management including the engine intake and exhaust system, boosting devices and the EGR system and to select the best possible technical solution. With respect to the power target of 45 kW and scavenging demands of the two-cylinder two-stroke engine with a displacement of 0.73 l, a two-stage boosting architecture was required. Further, to allow engine scavenging at any operation, supercharger had to be integrated in the air loop. Various air loop system layouts and concepts were assessed based on the 1-D steady state simulation at full and part load with respect to the fuel consumption.

3D simulations of internal combustion engines are usually based on statistical approaches (RANS) that may not allow predicting cycle-to-cycle variations (CCV) or transient speeds because part of this information is lost by the averaging procedure. To simulate such phenomena, it requires time resolved approaches. Therefore, large eddy simulation (LES), which only involves a spatial averaging, appears to be a very promising tool. An LES approach is applied to simulate the flow field inside one cylinder taken from a real four-valve diesel engine mounted on an experimental particle image velocimetry (PIV) bench. Preliminary tests are carried out to evaluate the industrial code capabilities. A multi-cycle calculation is computed in cold flow, in order to evaluate its ability to simulate cycle-to-cycle variations (CCV).

The description of the supply pressure hydraulic circuit and the couplings between its components are presented. A comparison between simulations and experiments is carried out. Using some linear facilities, it is possible to conclude that the low frequency modes mainly correspond to the wave effects of hydraulic lines which connect valves to each other. In order to maintain a pressure in the supply circuit, an electronic pressure control is necessary. The design of a control law needs to build different linear models for different levels of pressure since the system is very non linear. Three transfer functions are found for three pressure levels. These transfer functions are very similar to the ones used by the automatic control department and obtained by experiments. Using these transfer functions it is possible to design the control law.

Atomizing systems must be able to form sprays with predetermined characteristics. There are affected by the shape of the injector as well as external conditions. Thus, in order to avoid numerous experiments, this is necessary to develop predictive atomization models able to deal with the complete atomization process. This can be done using a Eulerian model for primary break-up. This approach describes the flow continuously from inside the injector to the dispersed spray region. In this paper the Eulerian multiphase approach and the Eulerian single-phase approach are compared and the results lead to an intermediate quasi-multiphase approach for describing the spray core. Finally a transition zone permits to represent the diluted spray region by using the classical Lagrangian approach to benefit of the experience accumulated on this method, in particular for the vaporization and the combustion.

In order to design vehicles with diminished gCO2/km emissions level, car manufacturers aim at reducing the weight of their vehicles. One of the solutions advocated by the automotive industry consists in the replacement of metallic parts by lighter systems made of polymer reinforced composites. Unfortunately, the numerical simulations set to evaluate the vibratory and acoustic performances of systems made of this kind of materials are often not sufficiently effective and robust so that convincing test/simulation correlations are rarely met. Indeed, for polymer-based materials, numerous parameters affect the vibroacoustic behavior. On the one hand, it is well known that the viscoelastic properties (Storage -Young- and dissipative moduli) of polymers depend on the temperature, loading frequency and sometimes the humidity content.

This paper presents an investigation on the experimental determination of some characteristics of the flow issuing from a swirl injector dedicated to direct-injection spark-ignited engines. The reproducibility, from one injection to another, of the temporal evolution of the liquid flow characteristics during the opening of the injector was investigated. This was achieved by using a high-speed film camera set at 8,000 images/s. The resulting visualizations allowed us to measure the evolution of the penetration length and velocity as well as of the liquid cone angle. It was found that the spray produced is a low momentum spray whose penetration length and velocity are small. The good reproducibility of the temporal evolution of the liquid flow characteristics has been obtained, except for the liquid cone angle during the opening stage. A fast-shutter video camera was also used to make images of the early development of the issuing liquid flow.

A new simulation approach to the modeling of the whole fuel injection process within a common-rail fuel injection system for direct-injection gasoline engines, including the pressure-swirl atomizer and the conical hollow-cone spray formed at the nozzle exit, is presented. The flow development in the common-rail fuel injection system is simulated using an 1-D model which accounts for the wave dynamics within the system and predicts the actual injection pressure and injection rate throughout the nozzle. The details of the flow inside its various flow passages and the discharge hole of the pressure-swirl atomizer are investigated using a two-phase CFD model which calculates the location of the liquid-gas interface using the VOF method and estimates the transient formation of the liquid film developing on the walls of the discharge hole due to the centrifugal forces acting on the swirling fluid.

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.