Abstract
In the last years, emissions standards for internal combustion engines are becoming more and more restrictive, particularly for NOx and soot emissions from Diesel engines. In order to comply with these requirements, OEMs have to face with innovative combustion concepts and/or sophisticate after-treatment devices. In both cases, the role of the Engine Management System (EMS) is increasingly essential, following the large number of actuators and sensors introduced and the need to meet customer expectations on performance and comfort. On the other hand, the large number of control variables to be tuned imposes a massive recourse to the experimental testing which is poorly sustainable in terms of time and money. In order to reduce the experimental effort and the time to market, the application of simulation models for EMS calibration has become fundamental. Predictive models, validated against a limited amount of experimental data, allow performing detailed analysis on the influence of engine control variables on pollutants, comfort and performance.In this paper, a simulation analysis on the impact of injection pattern and Exhaust Gas Recirculation (EGR) rate on fuel consumption, combustion noise, NO and soot emissions is presented for an automotive Common-Rail Diesel engine. Simulations are accomplished by means of a quasi-dimensional multi-zone model of in-cylinder processes. Furthermore a methodology for in-cylinder pressure processing is presented to estimate combustion noise contribution to radiated noise.Model validation is carried out by comparing simulated in-cylinder pressure traces and exhaust emissions with experimental data measured at the test bench in steady-state conditions. Effects of control variables on engine performance, noise and pollutants are analyzed by imposing significant deviation of EGR rate and injection pattern (i.e. rail pressure, start-of-injection, number of injections). The results evidence that quasi-dimensional in-cylinder models can be effective in supporting the engine control design toward the optimal tuning of EMS with significant saving of time and money.
Highlights
The interest in Diesel engines for automotive application has dramatically grown in the last decade, due to the benefits gained with the introduction of common-rail system and electronic control
The present section analyzes the impact of combustion control variables, namely fuel injection pattern and Exhaust Gas Recirculation (EGR) rate, on heat release rate, in-cylinder pressure and, noise and pollutants emissions of NO and soot
The analysis is based on the multi-zone model simulations coupled with the methodology for combustion noise prediction
Summary
The interest in Diesel engines for automotive application has dramatically grown in the last decade, due to the benefits gained with the introduction of common-rail system and electronic control. The drawback is the increase of combustion noise, due to the large delay of premixed combustion up to the Top Dead Center (TDC) that results in a dramatic and sharp increase of in-cylinder pressure (Torregrosa et al, 2011) In this context, it is clear that a suitable design of engine control strategies is fundamental in order to overcome with the simultaneous and opposite impact of combustion law on NOx/soot emissions and combustion noise. Many advanced models are available in the literature, based on the complete 3D description of turbulent, multi-phase flow field inside the cylinder (Gang and Tao, 2010; Lopez et al, 2013; Javadi Rad et al, 2010) Despite their accuracy, these models present a large computational demand and are oriented to engine design (combustion chamber shaping, fuel jet/air interaction, swirl) rather than to control design application. Injection and ignition delay and a methodology to estimate the combustion noise
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