Search Results

The authors present the supervisory control of a parallel hybrid powertrain, focusing on several issues related to the real-time implementation of optimal control based techniques, such as the Equivalent Consumption Minimization Strategies (ECMS). Real-time implementation is introduced as an intermediate step of a complete chain of tools aimed at investigating the supervisory control problem. These tools comprise an offline optimizer based on Pontryagin Minimum Principle (PMP), a two-layer real-time control structure, and a modular engine-in-the-loop test bench. Control results are presented for a regulatory drive cycle with the aim of illustrating the benefits of optimal control in terms of fuel economy, the role of the optimization constraints dictated by drivability requirements, and the effectiveness of the feedback rule proposed for the adaptation of the equivalence factor (Lagrange multiplier).

A methodology has been developed to determine, for every cycle on which significant knock is detected, the area in which self-ignition occurs. This methodology is based on the exploitation by a dedicated algorithm of a minimum of 4 simultaneous combustion chamber pressure measurements. The algorithm has been first tested on the results of engine knocking simulation, then applied with success on a single-cylinder engine equipped with classical pressure transducers and with an instrumented cylinder head gasket developed for this application. The results obtained with these two kinds of transducers on several engine configurations and tunings are similar. If the timing and intensity of knock events depend on all engine parameters, its location is especially sensitive to such design parameters as fluid motion into the combustion chamber and spark plug position.

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

An unified model with a single set of kinetic parameters has been proposed for modeling laminar flame velocities of several alkanes using detailed kinetic mechanisms automatically generated by the EXGAS software. The validations were based on recent data of the literature. The studied compounds are methane, ethane, propane, n-butane, n-pentane, n-heptane, iso-octane, and two mixtures for natural gas and surrogate gasoline fuel. Investigated conditions are the following: unburned gases temperature was varied from 300 to 600 K, pressures from 0.5 to 25 bar, and equivalence ratios range from 0.4 to 2. For the overall studied compounds, the agreement between measured and predicted laminar burning velocities is quite good.

In the context of low consumption and low emissions engines development, combustion processes modeling is a challenging subject as the requirements for accurately controlled pollutant emissions are becoming more stringent. From a scientific point of view, it is a major source of in-depth investigations as the chemical processes involved are strongly coupled to the flow characteristics. Among the various approaches developed recently to account for these processes in realistic configurations, tabulated techniques appear to be a promising way. They induce a good compromise between the accuracy of detailed chemistry and the computational time necessary to calculate complex configurations. Tabulation approaches were firstly developed to address the modeling of species concentrations in stationary combustors. They consist basically of pre-computed chemical kinetics using detailed mechanisms.

While fuel efficiency has to be improved, future Diesel engine emission standards will further restrict vehicle emissions, particularly of nitrogen oxides. Increased in-cylinder filling is recognized as a key factor in addressing this issue, which calls for advanced design of air and exhaust gas recirculation circuits and high cooling capabilities. As one possible solution, this paper presents a 2-stage boosting breathing architecture, specially dedicated to improving the trade-off between emissions and fuel consumption instead of seeking to improve specific power on a large family vehicle equipped with a 1.6-liter Diesel engine. In order to do it, turbocharger matching was specifically optimized to minimize engine-out NOx emissions at part-load and consumption under common driving conditions. Engine speed and load were analyzed on the European driving cycle. The key operating points and associated upper boundary for NOx emission were identified.

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 purpose of the 4-SPACE (4-Stroke Powered gasoline Auto-ignition Controlled combustion Engine) industrial research project is to research and develop an innovative controlled auto-ignition combustion process for lean burn automotive gasoline 4-stroke engines application. The engine concepts to be developed could have the potential to replace the existing stoichiometric / 3-way catalyst automotive spark ignition 4-stroke engines by offering the potential to meet the most stringent EURO 4 emissions limits in the year 2005 without requiring DeNOx catalyst technology. A reduction of fuel consumption and therefore of corresponding CO2 emissions of 15 to 20% in average urban conditions of use, is expected for the « 4-SPACE » lean burn 4-stroke engine with additional reduction of CO emissions.

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.

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 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.

NOx adsorbers are very sensitive to sulfur poisoning and future fuel standards are unlikely to be sufficient to prevent the system from requiring periodic desulfation procedures. The purpose of this paper is to present the effects of low fuel sulfur content such as 50 ppm and 10 ppm on the NOx adsorber efficiency for a diesel application. Through this study, the influence of the substrate cell geometry has also been assessed. The use of a 10 ppm sulfur fuel is not enough to maintain, at a high level, the NOx adsorber performance during a 40,000 km aging test. The desulfation criterion (efficiency loss of 30%) is reached after the first 16,000 km. However, the desulfation operation is not enough to recover the initial catalyst performance and the poisoning velocity increases as the catalyst ages. The hexagonal cell substrate catalyst is less sensitive to sulfur poisoning than a square cell substrate catalyst so that its desulfation frequency is much lower.

In the context of CO₂ emission regulations and increase of energy prices, the downsizing of engine displacement is a widely discussed solution that allows a reduction of fuel consumption. However, high power density is required in order to maintain the power output and a good driveability. This study demonstrates the potential to strongly increase the specific power of High Speed Diesel Injection (HSDI) diesel engines. It includes the technological requirements to achieve high specific power and the optimal combination of engine settings to maximize specific power. The results are based on experimental work performed with a prototype single-cylinder engine (compression ratio of 14). Tests were conducted at full load, 4000 rpm. Part load requirements are also taken into account in the engine definition to be compatible with the targets of new emission standards.

Latest emissions standards impose very low NOx and particle emissions that have led to new Diesel combustion operating conditions, such as low temperature combustion (LTC). The principle of LTC is based on enhancing air fuel mixing and reducing combustion temperature, reducing raw nitrogen oxides (NOx) and particle emissions. However, new difficulties have arisen. LTC is typically achieved through high dilution rates and low CR, resulting in increased auto-ignition delay that produces significant noise and deteriorates the combustion phasing. At the same time, lower combustion temperature and reduced oxygen concentration increases hydrocarbon (HC) and carbon oxide (CO) emissions, which can be problematic at low load. Therefore, if LTC is a promising solution to meet future emission regulations, it imposes a new emissions, fuel consumption and noise trade-off. For this, the injection strategy is the most direct mean of controlling the heat release profile and fuel air mixture.

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.

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.

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 influence of the type of fuel and the feeding means to a DOC, in order to regenerate a DPF, was investigated. Diesel fuel in cylinder late post-injection was compared to the injection in the exhaust line, through an exhaust port injector, of diesel fuel, B10 (diesel fuel containing 10% of esters) and gasoline. Diesel fuel exhaust injection resulted in a deteriorated conversion efficiency, while the incorporation of esters to the diesel fuel was demonstrated to have no influence. Gasoline exhaust injection led to less HC slip than diesel fuels. Temperature dynamics resulting from injection steps showed taught that the shorter the hydrocarbons (within the tested fuels), the slower the response. These differences can be caught by simple models, leading to interesting opportunities for the model-based control of the DPF inlet temperature during active regenerations.

Penetration and combustion of fuel sprays is studied in conditions similar to gasoline direct injection engines. A closed pressurized and heated injection cell is used. It is equipped with quartz windows providing large optical accesses. A homogeneous flammable mixture is introduced in the cell and ignited to raise the internal pressure and temperature. Liquid fuel is injected at the time when the desired thermodynamic conditions are reached. Conditions representative of late injection in a direct-injection engine are selected. Gasoline spray ignition and combustion is provided by a spark plug with long electrodes, locating the electrode gap right in the middle of the spray. The combustion does not reach the wall, which makes this experiment interesting for the validation of combustion in CFD codes. Two pressure swirl injectors with spray angles of 60 and 90 degree are used. The fuel is iso-octane with 5% 3-pentanone as tracer.

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.