Patrice Seers

A comparison of two control methods for vehicle stability control by direct yaw moment

This paper proposes a comparison study of two vehicle stability control methods by direct yaw-moment control (DYC): a PID and a sliding controller. For the purpose of this study, control systems are based solely on vehicle side-slip angle state feedback and the lateral dynamics of the 2 DOF vehicle model are used to establish the desired response. Close-loop dynamics of the PID controller are determined with the pole placement method, and an anti-windup strategy is adopted to respond to the tire’s nonlinear characteristics. The comparison study was performed by computer simulations with a 14 DOF nonlinear vehicle model validated with experimental data. The controllers are evaluated for typical severe manoeuvres on low friction road surfaces. It is found that despite their fundamental differences, the control methods provide comparable performances for the cases studied.

Influence of O2-enriched intake air with CO2 dilution on the combustion process of an optically accessible spark-ignition engine

Oxygen-enriched air combustion has been extensively studied, but not for internal-combustion engines. This paper presents how oxygen-enriched intake air influences early flame growth and the combustion process, and looks at how oxygen (O2) enrichment translates into resistance to carbon dioxide (CO2) dilution. The experiments were conducted with an optical single-cylinder engine instrumented with an in-cylinder pressure transducer and a high-speed camera to monitor early flame growth. During the experiments, O2 concentrations were varied from 18% to 29%, while CO2 was varied from 0% to 35%. The main findings are that O2 addition speeds up the combustion process and renders the flame more resistant to CO2 dilution. It was observed that the amount of CO2 can be significantly increased to reduce the combustion process to a level similar to that with air. Finally, laminar flame speed correlated well with early flame growth and fully developed turbulent combustion periods.

Calibration strategy of diesel-fuel spray atomization models using a design of experiment method

The Reitz and Diwakar and the KHRT atomization models are widely used for high-pressure diesel-fuel spray. The constants in both models must be calibrated to correctly predict the injection process based on the nozzle geometry, injection conditions, and fuel. Calibration can be significantly time-consuming given the four constants in both models. This paper suggests a strategy to assess the impact of models’ constants on spray tip penetration and mean droplet-diameter predictions on a reference case, with an injection pressure of 700 bar, to characterize the influence of the atomization model’s calibration. The assessment used a design of experiment method (DOE), which demonstrated the important interaction between constants on the results. Obtained calibrations were used for comparing the models’ performances qualitatively and quantitatively by accounting for spray and air-entrainment characteristics. Both models gave similar results, but the KHRT model yielded a better spray shape. Finally, based on DOE results, a method is proposed to modify the model’s constants for higher pressures (900 and 1300 bar).

Determination of fuel droplet evaporation based on multiple thermocouple sizes

Fuel droplet evaporation is an important process in fuel spray such as in internal combustion engine and gas turbine. Experimental data of fuel droplet evaporation are important to the validation of heat and mass transfer models which in turn are used in fuel spray modeling. This paper presents experimental data of evaporating butanol and nheptane droplets under warm forced convection. The droplets were suspended by thermocouple fibres to also obtain fuel droplets temperature. Different thermocouple diameters were used to determine the mean evaporation rate without thermocouple fibres which is extrapolated by plotting the mean evaporation rate of the droplet as a function of the thermocouple diameter squared. By using thermocouple it is also possible to obtain the fuel droplet temperature history which shows, for butanol, that most of the evaporation process takes place at a constant droplet temperature. On the other hand, for a volatile substance such as n-heptane, the droplet temperature is characterized by a continuously transient change of droplet temperature. Finally, the results of a model based on the energy balance of the fuel droplet shows the repartition of the relative importance of convection, conduction and radiation for different thermocouple fibre diameters.

Numerical Prediction of Gaseous Aerosol Precursors and Particles in an Aircraft Engine

Aviation-produced particulate matter has a direct impact on climate, atmospheric composition at flight altitudes, and local air quality in the vicinity of airports. The formation of soot and gaseous aerosol precursors inside the combustor and during gas expansion in turbine stages and nozzles must be addressed before the real impact of aircraft engines with respect to particulate matter emissions can be assessed. To design strategies to reduce particulate matter emissions, the development of a zero-/one-dimensional gas-turbine model is proposed, taking into account combustor and postcombustor flow operating over the landing/takeoff cycles with a detailed kerosene jet-A1 kinetics scheme, including a soot-dynamics model. This approach is very efficient computationally and may be clearly satisfying for parametric studies or in a predesign step. First, the model’s predictive capacity for capturing the main features of gas-turbine combustion as well as the expansion of combustion products in the turbine and no...

A Passive Nonlinear Damping Design for a Road Race Car Application

A suspension system does not merely isolate a vehicle from the shocks and vibrations induced by the road surface. It also keeps the wheels in contact with the road, ensuring vehicle stability and control. In order to properly determine the stiffness and damping parameters of a Formula SAE, models for a quarter car and a seven degree-of-freedom car (DOF-7) were developed based upon Newton’s second law. These were built using MatLab/Simulink. The quarter car model was taken first, to study the effect of four (4) suspension parameters on the tires’ vertical load fluctuations. The results were then used to optimize suspension parameters for the 7-DOF model, taking the bounce, roll and pitch motions of the chassis into account in addition to its four-wheel hops. Track data was acquired and used as input to the model. Nonlinear damping was implemented in the 7-DOF model to study the car’s behavior. The simulation results show that very high damping helps control the slow motions of the chassis, while at higher wheel hop speeds, a low damping ratio minimizes the tires’ vertical load fluctuations.

Comparison between LES and experimental round jet for diesel fuel spray

Over the last few decades, Large Eddy Simulation (LES) have spread over the fuel spray simulation field thanks to its capability to capture turbulence. However, the use of traditional Lagrangian Eulerian simulations is usually based on the point particle hypothesis making the use of fine grid, as those needed by LES, difficult to validate because of the dependency of the solution. This problem is coupled to the lack of experimental results on the Eulerian phase turbulence. This paper aims to assess the representation of the Eulerian phase of LES spray simulations by using the canonical case of a round turbulent jet flow. The latter’s initial conditions are based on the entrained air characteristics of a RANS diesel fuel spray simulation. Validation is handled by comparing LES simulation results of a turbulent jet to experimental one from the literature. Thus, mean profiles as well as turbulent quantities and numerical characteristics such as spectrum and resolution quality index are used in the validation process.

Unsteady Flow Analysis in a Fired Briggs-Stratton Internal Combustion Engine

Unsteady velocity measurements made near the spark-plug location of a fired Briggs and Stratton IC engine using a single-component LDV fiber-optic spark-plug LDV probe are reported. An off-the shelf engine was first equipped with an IMPCO carburetor adapter to allow the engine run using methane gas. Velocity data obtained during the engine start and the engine run were analyzed using high-pass filtering, wavelet decomposition, proper orthogonal decomposition, and wavelet decomposition together with proper orthogonal decomposition techniques to separate the mean and fluctuating velocity components. Data was further analyzed to determine the standard deviation of the fluctuating velocity signal and the cross correlation between the pressure and velocity signals. Results show that mean velocity delayed by 0.034 seconds show a high correlation with the pressure signal.

Comparison of three evaporation models combined to the distillation curve model for multicomponent fuel droplet evaporation

The objective of this paper is to present a validation of the distillation curve (DC) model with experimental results. Along this validation, three different droplet heating and vaporization models are also compared to see how well they are able to predict the droplet change of diameter. As the DC model requires knowing the distillation curve of complex fuel, it is proposed to use a simplified distillation curve based only on the boiling range temperatures which is more easily known than the exact distillation curve of a given fuel. The simulation results with kerosene fuel show that models 1 and 2 show exactly the same droplet lifetime and temperature profiles under quiescent hot environment. However, the behavior is different when forced convection is present. The simplified DC model capture the general behavior of multicomponent fuel evaporation process. Finally, an experiment was conducted with a suspended droplet of gasoline and all three models show different temperature and diameter profiles.

Evaporation time of gasoline and diesel fuel droplets on a hot plate : the influence of fuel deposits

The objective of this paper is to present experimental results of multicomponent fuel droplets impinging on a hot surface in order to quantify the influence of fuel build-up deposits on the evaporation time. The experiments were conducted with gasoline and diesel fuels to first obtain curves of evaporation time as a function of plate temperature. Based on these curves the Nukiyama and Leindenfrost temperatures were identified. In a second step, the effect of fuel deposit on the droplet evaporation time was studied. Based on the above evaporation time curves, plate temperatures were chosen as to offer a similar evaporation time but at temperatures below and above the Nukiyama and Leindenfrost temperatures respectively. This was done in order to isolate the effect of fuel deposits from the different evaporation mechanisms. The evaporation of successive impinging droplets was then measured. The results hence obtained indeed showed that the fuel deposit has a different impact on the evaporation time according the evaporating mechanism or equivalently the plate temperature. For plate temperatures lower than the Nukiyama temperature, gasoline and diesel fuel droplets showed an increase of their evaporation time as the amount of successive impinging droplets increased. The trend was reversed for plate temperatures above the Leindenfrost temperature. A hypothesis for this latter case is that the fuel deposit disrupts the vapor layer supporting the droplet and therefore provides a greater heat flux to the evaporating droplet. Finally, droplet evaporation times as a function of plate temperature were measured with an initial fuel deposit covering the plate. These results in turn showed that the global thermal diffusivity and porosity of the surface are changed by the presence of the fuel deposit. The consequence of these property changes are then shown to have a direct and global impact on the fuel evaporation time curves.Copyright