H. Climent

Assessment of a sequentially turbocharged diesel engine on real-life driving cycles

The article presents the development of the control manager of a parallel sequential turbocharger system. This control manager must decide the transition between the different operation modes of the boosting system. The control manager must protect the system from surge and over-speed risks.The methodology followed in the development process was based on the use of concurrence survey data from a similar engine, the simulation with a 1D code and finally the assessment on engine test bench. Real-life driving cycles were used during the development process, which were acquired in three different driving scenarios (city, road and mountain road).

Effect of the numerical scheme resolution on quasi-2D simulation of an automotive radial turbine under highly pulsating flow

Automotive turbocharger turbines usually work under pulsating flow because of the sequential nature of engine breathing. However, existing turbine models are typically based on quasi-steady assumptions. In this paper a model where the volute is calculated in a quasi-2D scheme is presented. The objective of this work is to quantify and analyse the effect of the numerical resolution scheme used in the volute model. The conditions imposed upstream are isentropic pressure pulsations with different amplitude and frequency. The volute is computed using a finite volume approach considering the tangential and radial velocity components. The stator and rotor are assumed to be quasi-steady. In this paper, different integration and spatial reconstruction schemes are explored. The spatial reconstruction is based on the MUSCL method with different slope limiters fulfilling the TVD criterion. The model results are assessed against 3D U-RANS calculations. The results show that under low frequency pressure pulses all the schemes lead to similar solutions. But, for high frequency pulsation the results can be very different depending upon the selected scheme. This may have an impact in noise emission predictions.

ECU-oriented models for NOx prediction. Part 2: adaptive estimation by using an NOx sensor

The implantation of nitrogen oxide sensors in diesel engines is necessary in order to track emissions at the engine exhaust line for diagnosis and control of the after-treatment devices. However, the use of models is still necessary since the sensor outputs are delayed and filtered. The present paper deals with the problem of the nitrogen oxide estimation in two parts; Part 1 deals with a control-oriented model for the nitrogen oxide estimation, while Part 2 presents data fusion of the model and the sensor to improve the estimation, which is presented in the following. The use of models for the nitrogen oxide estimation is an alternative but the drift and the ageing are still issues. In order to overcome this problem, the fusion of different signals can be carried out in a smart way by means of a Kalman filter. There exist different ways of presenting this fusion, from directly tracking the bias to updating the model parameters. For this, different algorithms are proposed in this paper with the aim of correcting the model output. Furthermore, the estimation of the actual nitrogen oxide concentration, by preventing sensor delay and filtering, is also integrated in the algorithm, which is a suitable strategy for combining nitrogen oxide sensors and models on an onboard basis.

A New Model for Matching Advanced Boosting Systems to Automotive Diesel Engines

This work has been partially financed by the Univeristat Politecnica de Valencia through the Programa de Apoyo a la Investigacion y Desarrollo 2012, project PAID-06-2012 DECOAH.

Analysis of shock capturing methods for chemical species transport in unsteady compressible flow

Abstract This paper presents a chemical species transport model to account for variable composition and gas properties along the flow path in internal combustion engines. The numerical solution to adapt the gas dynamic model to chemical species transport in boundary conditions by means of the Method of Characteristics and in volumes by means of a filling and emptying model is described. The performance for chemical species transport in 1D elements of shock-capturing methods, such as the two-step Lax–Wendroff method and the Sweby’s TVD scheme considering several flux limiter definitions, is carried out by means of shock-tube tests. The influence of the fluid modelling as perfect or non-perfect gas on the numerical methods features and the flow characteristics on shock-tube results are analysed.

A collocation method to compute one-dimensional flow models in intake and exhaust systems of internal combustion engines

In this paper, an analytical approximate solution of Euler equations is obtained by a collocation method. The collocation method uses two variables Chebyshev polynomial basis and collocation coefficients are obtained solving polynomial equations by means of homotopy methods.

Contribution to the Understanding of Cold Pulsating Flow Influence in the Efficiency of Small Radial Turbines for Turbochargers

In the present paper an unsteady approach to determine the performance of a small radial inflow turbine working under cold pulsating flow is presented. It has been concluded that a reasonably good characterization of turbine behavior working with pulsating flow can be obtained using in a quasi-steady way models of the turbine isentropic efficiency and turbocharger mechanical efficiency. Both models have been fitted using data obtained from a steady flow characterization procedure.Turbocharger measured parameters from the cold pulsating flow campaign have been compared with the ones obtained from one-dimensional gas-dynamics computational modeling. The modeling approach is based on quasi-steady isentropic and mechanical efficiency models. Reasonably good accuracy in compressor and turbine variables prediction has been obtained for most of the operative conditions. Influence of amplitude and frequency of the pulsating flow over the instantaneous and average turbine efficiency has been studied to put some light on the analysis of the involved physical phenomena. The main conclusion is that the biggest effect of unsteady flow on turbine efficiency is through the influence on blade jet to speed ratio. It has been also concluded that for the same average blade to jet speed ratio pulses amplitude does not influence turbine efficiency when it is closed but yes at other VGT positions. The effect of pulses frequency is less evident and only influences VGT performance at the highest VGT openings.Copyright

Influence of ambient temperature on diesel engine raw pollutants and fuel consumption in different driving cycles

The effect of low ambient temperature on diesel raw pollutant emissions is analysed in two different driving cycles: NEDC and WLTC. The study is focused on hydrocarbons, carbon monoxide, nitrogen oxides and fuel consumption. Tests are conducted at cold start in a HSDI light-duty diesel engine with two levels of ambient temperature: 20 °C and −7 °C. Results showed a general detriment of pollutant emissions and break thermal efficiency at low ambient temperatures. NOx is increased around 250% in both cycles when running at low temperatures. Effect on hydrocarbons is more noticeable in the NEDC, where it rises in 270%, compared with the 150% of increase in the WLTC. In the case of carbon monoxide, uncorrelated tendencies are observed between both driving cycles. Concerning the NEDC, carbon monoxide emissions increase up to 125%, while at the WLTC, they are reduced up to 20%. Finally, from the point of view of the thermal efficiency, a reduction of nearly 10% in the NEDC is observed. However, no fuel penalty is spotted regarding the WLTC.

Effect of boosting system architecture and thermomechanical limits on diesel engine performance: Part-I—Steady-state operation

Internal combustion engine developments are more focused on efficiency optimization and emission reduction for the upcoming future. To achieve these goals, technologies like downsizing and downspeeding are needed to be developed according to the requirement. These modifications on thermal engines are able to reduce fuel consumption and C O 2 emission. However, implementation of these kind of technologies asks for right and efficient charging systems. This article consists of study of different boosting systems and architectures (single- and two-stage) with combination of different charging systems like superchargers and e-boosters. A parametric study is carried out with a zero-dimensional engine model to analyze and compare the effects of these different architectures on the same base engine. The impact of thermomechanical limits, turbo sizes and other engine development option characterizations are proposed to improve fuel consumption, maximum power and performance of the downsized/downspeeded diesel engines.

Analysis of the Air-Fuel Mixture Control in Natural Gas Fuelled Turbocharged Engines

The use of natural gas in medium and heavy duty engines for public transportation is a promising way for reducing exhaust emissions. Computer simulations, coupled with engine tests, have arisen as a valuable methodology to study the gas exchange processes inside intake and exhaust manifolds. A wave action model is set up in order to simulate a natural gas fuelled turbocharged engine. Once the modeling results show good agreement when comparing with measured data at different running conditions in terms of fluid dynamic properties, the model is used to study the air-fuel mixture process in the intake manifold and optimize the injection system behavior. Comparisons of modeled air-fuel composition in the cylinders are performed with both single and multi-point injection strategies. These cylinder to cylinder air-fuel mixture dispersion problems are analyzed at both steady and transient engine running conditions. Steady operation is performed correctly when using single-point injection since the gas mixer upstream the throttle valve enhances the mixing process. However, significant gas dispersion among cylinders appears during an engine load transient. With multi-point injection the critical parameter is the injection timing, since it is usually larger than the intake stroke period and, if it is not conveniently arranged, significant natural gas dispersion among cylinders may appear at both steady and transient running conditions.Copyright