Pascal Higelin

Parametric optimization of a new hybrid pneumatic-combustion engine concept

Abstract Although internal combustion engines display high overall maximum global efficiencies, this potential cannot be fully exploited in automotive applications: in real conditions, the average engine load (and thus efficiency) is quite low and the kinetic energy during a braking phase is lost. One solution to this problem is to switch to a new hybrid pneumatic-combustion engine concept, which is able to store energy in the form of compressed air. This energy can be issued from a braking phase or from a combustion phase at low power. The potential energy from the air tank can then be restored to start the engine, use the stored air to drive the engine as a pneumatic motor at low load or charge the engine at full load. Optimization of the compressed air tank maximum pressure and volume as well as the operating mode switching strategy provides an improvement in terms of fuel economy as high as 31 per cent if combined with engine downsizing.

A simple method for robust control design, application on a non-linear and delayed system: engine torque control

Abstract This paper presents a simple method for designing a robust controller which can be used on uncertain and non-linear systems. As an extension of the method, the case of delayed systems is examined. The successive steps of the method are: non-linearity analysis and description, system linearization and identification, operating model design by minimization of a weighted frequencies criteria, model uncertainty design, PI and LQ controller design with robust property verification. A Smith predictor is included in the global control scheme to take the delay of the system into account. The application is a design of a robust controller for engine torque control.

Residual gas fraction measurement and computation

Abstract To meet future pollutant emissions standards, it is crucial to be able to estimate not only the cycle-by-cycle mass but also the cycle-by-cycle composition of the combustion chamber charge. This charge consists of fresh air, fuel, and residual gas from the previous cycle. Unfortunately, the residual gas fraction cannot be directly measured. Two experimental methods have been designed to determine the residual gas fraction. The reference method is based on an in-cylinder sampling method. The second one is based on a hydrocarbon (HC) analysis of the exhaust gases. Two models have been compared to the experimental results. A one-dimensional computational fluid dynamics (CFD) code (WAVE) and a zero-dimensional model (AMESIM), which takes into account gas compressibility. The aim of the study was to compare the results of CFD codes (one- and zero-dimensional) to experimental results. If the code is validated by the experiments, it should be possible to determine residual gas fractions without needing a large experimental set-up.

Validation and Application of a New 0D Flame/Wall Interaction Sub Model for SI Engines

To improve the prediction of the combustion processes in spark ignition engines, a 0D flame/wall interaction submodel has been developed. A two-zones combustion model is implemented and the designed submodel for the flame/wall interaction is included. The flame/wall interaction phenomenon is conceived as a dimensionless function multiplying the burning rate equation. The submodel considers the cylinder shape and the flame surface that spreads inside the combustion chamber. The designed function represents the influence of the cylinder walls while the flame surface propagates across the cylinder. To determine the validity of the combustion model and the flame/wall interaction submodel, the system was tested using the available measurements on a 2 liter SI engine. The model was validated by comparing simulated cylinder pressure and energy release rate with measurements. A good agreement between the implemented model and the measurements was obtained.

A high gain observer for enclosed mass estimation in a spark ignited engine

A high gain non linear observer is implemented to estimate the enclosed mass in the combustion chamber of a spark ignited engine. The observer uses the cylinder pressure measurement during the compression and combustion strokes to estimate the enclosed mass. An engine model is proposed and used as a virtual engine to build the observer. The model is validated by comparison with real measurements, obtained from experimental tests. The results of the observer are compared with the virtual engine model.

One Dimensional Modeling and Experimental Validation of Single Cylinder Pneumatic Combustion Hybrid Engine

The objective of this paper is to present and to validate a numerical model of a single-cylinder pneumatic-combustion hybrid engine. The model presented in this paper contains 0-D sub-models for non-spatially distributed components: Engine cylinder, Air tank, wall heat losses. 1-D sub-models for spatially distributed components are applied on the compressive gas flows in pipes (intake, exhaust and charging). Each pipe is discretized, using the Two-Steps Lax-Wendroff scheme (LW2) including Davis T.V.D. The boundaries conditions used at pipe ends are Method Of Characteristics (MOC) based. In the specific case of a valve, an original intermediate volume MOC based boundary condition is used. The numerical results provided by the engine model are compared with the experimental data obtained from a single cylinder prototype hybrid engine on a test bench operating in 4-stroke pneumatic pump and 4 stroke pneumatic motor modes. In each mode, the prediction of the mass flow rates, amplitude and timing of the charging pipe waves are satisfactory, without using any discharge coefficient. Indicated work and p-V diagrams are similar between simulation and measurements in the case of pneumatic pump mode. For the pneumatic motor mode the model underestimates cylinder pressure during the charging process.

Development and experimental validation of a new one-dimensional valve boundary condition based on the method of characteristics:

One-dimensional (1D) engine gas dynamic simulations are necessary in order to develop control laws for specific valve systems such as variable valve timing or the pneumatic hybrid engine. The keystone of 1D engine models is the valve boundary condition, where the pressure wave phenomenon into a pipe is created and the in-cylinder mass flowrate is determined. Most commercial or research simulation codes embed the method of characteristics (MOC) constant-pressure valve boundary condition from Benson. This constant-pressure model in its original form provides good results in most cases, but this paper shows that it does not converge for low valve opening and pressure ratio values, for which the characteristic lines become vertical. A solution to this problem cannot be found in the literature. The current paper presents a new MOC-based valve boundary condition that obviates convergence problems. The computational time of the proposed model is evaluated and compared with that of Benson’s model. The new valve boundary condition is validated experimentally on a valve gas dynamics test bench and compared with the original constant-pressure model. The study shows that results obtained with the proposed model are similar to data from both experiments and Benson’s model.

TWO OBSERVERS FOR IN-CYLINDER MASS ESTIMATION USING CYLINDER PRESSURE MEASUREMENTS

Abstract To meet future pollutant emissions Standards, it is crucial to be able to estimate the cycle by cycle in-cylinder mass and the composition of the combustion chamber charge. This charge consists of residual gas from the previous cycle, fresh air and fuel. Consequently, the estimation of the fresh air mass based on total in-cylinder mass is a function of the residual gas fraction. This estimation is essential to compute the fuel mass to be injected. This paper proposes two observers, based on a physical approach, that estimate the in-cylinder mass and composition using the cylinder pressure. To test the estimator, several parameters are varied, especially the cylinder pressure offset compensation and the exhaust gases temperature.

Energy Wall Losses Estimation of a Gasoline Engine Using a Sliding Mode Observer

This paper describes an innovative method to estimate the wall losses during the compression and combustion strokes of a gasoline engine using the cylinder pressure measurement. The estimation during the compression and combustion strokes allows to better represent the system during the combustion. A sliding mode observer is derived from a validated 0-D physical engine model and its convergence and stability are proved. The observer is validated using two different engine models: a one zone engine model and a two zones engine model with flame wall interaction. A good agreement between the estimation results and the model reference is observed, showing the interest of using closed loop strategies to estimate the wall losses in a SI engine.

Heat Transfer Investigation in an Engine ExhaustType Pulsating Flow

There are many engineering practical situations where heat is transferred under conditions of pulsating flow such as in the exhaust pipes of Internal Combustion Engines. In these conditions, heat transfer mechanism is affected by the pulsating flow parameters. The objective of the present work is to experimentally investigate heat transfers for pulsatile turbulent flows in a pipe. A unique experimental apparatus able to reproduce a pulsating flow representative of the engine exhaust has been designed. A stationary turbulent hot air flow with a Reynolds number of 30000, based on the time average velocity, is excited through a pulsating mechanism and exchanges thermal energy with a steel pipe. Pulsation frequency ranges from 10 to 95 Hz. The effects of pulsation frequency and pipe length are evaluated. It has been observed that flow pulsation enhances convective heat transfers in comparison with the steady case. The test-bench architecture let us to evidence that, when the flow is excited with a pulsation frequency equal to one of the resonance modes of the system, a local maximum of the heat transfers rate appears. Such behaviour has been found to be independent of the pipe length. Results also show that the actual Nusselt correlations to predict convective heat transfer are inaccurate for pulsating flows, suggesting that new correlations which account pulsation effects have to be proposed.