Effect of optimized EGR on fuel consumption Abstract: In recent years, more stringent requirements on performance, fuel economy and emissions have led to increasingly complicated engine configurations. This paper is a study into the potential benefits of an EGR MAP optimization for low fuel consumption and lower mass emission. Introduction: The narrower environmental restrictions are the current challenge that Diesel engine manufacturers are facing in the last years.
The demand on cleaner emissions (both for NOx and soot), the fuel consumption reduction and the customer claim for improved engine performance are variables that should be matched to attend the legislation and market requirements. The search for these problems solution is a target that needs to be continuously reached, as the limits for emissions are year-by-year being updated and becoming more and more severe. Also, fossil fuel saving is a must for the future trends due to the reduction of its global reserves, the high cost associated with new fuel sources research and the greenhouse effect.
Besides the external demands, the automotive industry is on a process to reduce costs and improve its efficacy. Time-to-market reduction, less validation tests and prototypes generation, smarter solutions and more robust design are only some of the achievements that are being sought. On this way, the use of numerical simulation is a powerful and significant tool. In order to reduce emission levels, some external engine features can be applied, such as EGR or after-treatment systems.
The optimization of the piston bowl and injector design may also bring significant improvements on NOx and soot reduction. Piston bowl profile, injector nozzle diameter and angle, injector position on combustion chamber, and calibration variables (injection start, fuel mass, etc.. ) are some of the parameters that can be set for this purpose. The larger use of EGR system is a trend for the upcoming Diesel engines as it is very effective to mitigate the NOx levels, reducing the flame temperature. On the other side, soot levels are increased due to poor oxygen offer.
The purpose of this paper is to describe an optimization study of the combustion design (intake and exhaust system, fuel system and piston bowl) for engines with EGR. The desirable design solution shall result in soot level reduction in order to compensate the effects of the gas recirculation. The understanding of combustion processes and their influence on engine and emissions performance were described by 1D simulation and detailed by 3D CFD. DoE tools were used to find the most appropriate design and the compromise relation between the variables mentioned above.
An engine. s combustion project aims at three specific goals: 1. Cleaner emissions 2. Low fuel consumption 3. High performance engines All of them are requirements for a competitive engine and to obey the new environmental regulations imposed by the new emissions standards These objectives can point to different directions. To minimize the NOx emission it is necessary to delay the injection, however the same delay can imply in a higher concentration of soot on the exhaustion gases, being necessary to obtain a compromised solution among them.
A design option is the use of Exhaust Gas Recirculation (EGR), commonly applied on Diesel engines to improve the emissions (cleaner emissions). In order to comply with the emissions standards, the rates of EGR are rising rapidly, changing the behavior of the combustion and requiring studies to observe more properly the effect of these gases on the combustion performance. For instance, the EUROV emissions standard will be institutionalized in Brazil and to attend this emission standard a higher rate of EGR needs to be imposed.
The EGR system does not affect the injection system. However, it influences the combustion because of the presence of burned fuel mixed with the air from the inlet system. The first and most basic EGR effect is the increase on the inlet air ratio after mixing with the EGR rate raise, and the consequence is a lower air density and reduction of the air mass trapped inside the cylinder. Even if the engine has an EGR cooler, this impact on the temperature is observed.
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