Vicente Bermúdez

Sensitivity of diesel engine thermodynamic cycle calculation to measurement errors and estimated parameters

The use of thermodynamic models for the calculation of the heat release law from the experimental in-cylinder pressure signal has been a common practice as a way to study the combustion process of internal combustion engines. However, the results of this procedure depend mainly on two factors: the validity of the assumed hypothesis and the quality of the measurement of the experimental parameters (both mean and instantaneous ones) used as input data. In this work a sensitivity study of a thermodynamic diagnostic model is presented, with the objective of evaluating the influence of errors in the measuring techniques or in the estimation of parameters on the main results, such as mean gas temperature, heat release and rate of heat release. In order to eliminate the effect of the uncertainty associated with the combustion process itself, the study focused on motored engine conditions. Otherwise, the effect of the inadequacy of the assumed hypothesis was eliminated by using as input in the diagnostic thermodynamic model the results from a predictive thermodynamic model with the same hypothesis as the diagnostic one, instead of an experimental pressure signal.

Modelling of turbocharged diesel engines in transient operation. Part 1: Insight into the relevant physical phenomena

Abstract A new calculation model, able to predict the engine performance during an engine transient, has been developed, based on an existing wave action code. Previously to the model development, the turbocharged diesel engines transient phenomena (turbocharger lag, thermal transient and energy transport delay) were deeply analysed on the basis of experimental information. The study has been focused on the load transient, i.e. torque increase from idle, at constant engine speed of a high speed direct injection (DI) turbocharged engine. Experimental load transient tests have been performed, with the aim of obtaining a combustion database during engine transient operation, to input into a combustion simulation submodel. The applied methodology allows the characterization of the transient combustion process in any DI turbocharged engine.

Study of the influence of nozzle seat type on injection rate and spray behaviour

A deep analysis of the injection rate characteristics and spray behaviour of the most used nozzle types in diesel engines [microSAC and valve covered orifice (VCO)] has been carried out. In order to compare the injection characteristics and the spray behaviour of both nozzle types, several experimental installations were used, such as the steady flow test rig, injection rate test rig, spray momentum test rig, and nitrogen test rig, to obtain a full hydrodynamic and spray characterization. The study of the flow in both nozzles was analysed under steady flow conditions in the steady flow test rig and in real unsteady flow conditions in the injection rate test rig and the spray momentum test rig. The macroscopic properties of the spray (tip penetration and spray cone angle) were characterized using a high-pressure test rig. From the point of view of the internal flow behaviour, the results showed interesting differences in the permeability of both nozzle geometries, with a higher discharge coefficient in the microSAC nozzle. However, from the point of view of air entrainment, the results showed a better quality of fuel-air mixing in the VCO nozzle. Besides the evidence from the experimental results, a theoretical analysis was carried out in order to identify the most important parameters that determine the spray behaviour and thus justify the different macroscopic behaviour of both nozzles.

Exhaust pressure pulsation observation from turbocharger instantaneous speed measurement

In internal combustion engines, instantaneous exhaust pressure measurements are difficult to perform in a production environment. The high temperature of the exhaust manifold and its pulsating character make its application to exhaust gas recirculation control algorithms impossible. In this paper an alternative method for estimating the exhaust pressure pulsation is presented. A numerical model is built which enables the exhaust pressure pulses to be predicted from instantaneous turbocharger speed measurements. Although the model is data based, a theoretical description of the process is also provided. This combined approach makes it possible to export the model for different engine operating points. Also, compressor contribution in the turbocharger speed pulsation is discussed extensively. The compressor contribution is initially neglected, and effects of this simplified approach are analysed.

Assessment by means of gas dynamic modelling of a pre-turbo diesel particulate filter configuration in a turbocharged HSDI diesel engine under full-load transient operation

Diesel particulate filters (DPF) are becoming a standard technology in diesel engines because of the need for compliance with forthcoming regulations regarding soot emissions. When a great degree of maturity in management of filtration and regeneration has been attained, the influence of the DPF placement on the engine performance emerges as a key issue to be properly addressed. The novelty of this work leads to the study of an unusual location of an aftertreatment device in the architecture of the turbocharged diesel engine exhaust line. The problem of the pre-turbo DPF placement is tackled comparing the engine response under full-load transient operation as opposed to the traditional DPF location downstream of the turbine. The study has been performed on the basis of a gas dynamic simulation of the engine, which has been validated with experimental data obtained under steady-state and transient conditions. The DPF response has been simulated with a model able to deal with the characteristic highly pulsating flow upstream of the turbine. Several levels of DPF soot loading have been considered to represent fully the most exigent conditions in terms of performance requirements. As a result, the main physical phenomena controlling the engine and DPF response and interaction have been identified. Placing the DPF upstream of the turbine will lead to a number of important advantages, owing to the continuous regeneration mode at which the DPF will operate, the lower pressure drop in the DPF, and the thermal energy storage in the DPF, which is very useful to mitigate ‘turbocharger lag’ during engine transient operation. These three effects have been evidenced with calculations performed using the validated model and the results have been fully analysed and discussed.

Methodology for measuring exhaust aerosol size distributions using an engine test under transient operating conditions

A study on the sources of variability in the measurement of particle size distribution using a two-stage dilution system and an engine exhaust particle sizer was conducted to obtain a comprehensive and repeatable methodology that can be used to measure the particle size distribution of aerosols emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement method; an evaluation of the influence of sampling factors, such as dilution system pre-conditioning; and a study of the effects of the dilution conditions, such as the dilution ratio and the dilution air temperature. An examination of the type and degree of influence of each studied factor is presented, recommendations for reducing variability are given and critical parameter values are identified to develop a highly reliable measurement methodology that could be applied to further studies on the effect of engine operating parameters on exhaust particle size distributions.

Analysis of heavy-duty turbocharged diesel engine response under cold transient operation with a pre-turbo aftertreatment exhaust manifold configuration

Diesel particulate filters are the most useful technology to reduce particulate matter from the exhaust gas of internal combustion engines. Although these devices have suffered an intense development in terms of the management of filtration and regeneration, the effect of the system location on the engine performance is still a key issue that needs to be properly addressed. The present work is focused on a computational study regarding the effects of a pre-turbo aftertreatment placement under full and partial load transient operation at constant engine speed and low wall temperature along the exhaust line. The aim of the paper is to provide a comprehensive understanding of the engine response to define the guidelines of a control strategy that is able to get the standards of engine driveability during sudden accelerations under restraining thermal transient conditions governed by the aftertreatment thermal inertia. The proposed strategy overcomes the lack of temperature at the inlet of the turbine caused by the thermal transient by means of the boost and EGR control. It leads to a proper management of the power in the exhaust gas for the expansion in the turbine.

Transient particle emission measurement with optical techniques

Particulate matter is responsible for some respiratory and cardiovascular diseases. In addition, it is one of the most important pollutants of high-speed direct injection (HSDI) passenger car engines. Current legislation requires particulate dilution tunnels for particulate matter measuring. However for development work, dilution tunnels are expensive and sometimes not useful since they are not able to quantify real-time particulate emissions during transient operation. In this study, the use of a continuous measurement opacimeter and a fast response HFID is proven to be a good alternative to obtain instantaneous particle mass emissions during transient operation (due to particulate matter consisting mainly of soot and SOF). Some methods and correlations available from literature, but developed for steady conditions, are evaluated during transient operation by comparing with mini-tunnel measurements during the entire MVEG-A transient cycle. A new correlation was also derived from this evaluation. Results for soot and SOF (obtained from the new correlation proposed) are compared with soot and SOF captured with particulate filters, which have been separated by means of an SOF extraction method. Finally, as an example of ECU design strategies using these sort of correlations, the EGR valve opening is optimized during transient operation. The optimization is performed while simultaneously taking into account instantaneous fuel consumption, particulate emissions (calculated with the proposed correlation) and other regulated engine pollutants.

A Comprehensive Study of Particle Size Distributions with the Use of PostInjection Strategies in DI Diesel Engines

Control strategies such as variations in injection pressure and timing have been used by researchers to reduce in-cylinder exhaust emissions and meet legislation standards. Postinjection has been studied for several years and is now well known as an efficient strategy for reducing soot emission. Diesel gaseous and particle mass emissions have been progressively reduced over the last twenty years as a consequence of increasingly restrictive emission legislation and the application of aftertreatment devices. The main objective of this work is to better understand the effect of postinjection on particle size distribution in diesel exhaust. The approach uses a modern, well-instrumented research engine test cell equipped with a flexible high pressure fuel injection system. The results of this work provide guidelines for developing strategies to reduce particle size distribution in diesel engines. A major improvement in particle size distribution was found in the accumulation mode by using a close postinjection of a small quantity of fuel. For reduction in nucleation mode, a relationship was found with close postinjections of large quantities of fuel.

Experimental correlations for transient soot measurement in diesel exhaust aerosol with light extinction, electrical mobility and diffusion charger sensor techniques

A study of soot measurement deviation using a diffusion charger sensor with three dilution ratios was conducted in order to obtain an optimum setting that can be used to obtain accurate measurements in terms of soot mass emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement settings in steady-state operating conditions; evaluation of the proposed setting under the New European Driving Cycle; and a study of correlations for different measurement techniques. These correlations provide a reliable tool for estimating soot emission from light extinction measurement or from accumulation particle mode concentration. There are several methods and correlations to estimate soot concentration in the literature but most of them were assessed for steady-state operating points. In this case, the correlations are obtained by more than 4000 points measured in transient conditions. The results of the new two correlations, with less than 4% deviation from the reference measurement, are presented in this paper.