Effects of piston bowl geometry on Reactivity Controlled Compression Ignition heat transfer and combustion losses at different engine loads

Abstract

This work investigates the effects of the piston bowl geometry on RCCI heat transfer and combustion losses and its repercussion on the engine efficiency. For this purpose, three piston geometries with compression ratio 14.4:1 have been studied and compared by means of computational modeling. In addition, the engine operating conditions proposed at low, medium and high load were also validated experimentally in a heavy-duty single-cylinder engine adapted for dual fuel operation. The engine speed was kept constant at 1200 rev/min during the research. Results suggest that heat flux through the piston surface represent the major portion of the heat transfer energy. Thus, the comparison of the three geometries demonstrates that reduced piston surface area and reduced charge motion, are the key factors to improve the gross indicated efficiency over the different engine loads. Moreover, it is found that a shallow piston geometry with a smooth transition from the center to the squish region, with a 16% reduced surface area, strongly improves the gross work at low load. However, this gain diminishes due to increased combustion losses as engine load increases. Finally, an intermediate geometry was confirmed as the best balanced piston geometry for RCCI operation over the three different loads.

A Combination of Swirl Ratio and Injection Strategy to Increase Engine Efficiency

“…CO2 emissions, as the main contributor to greenhouse effect, can be mitigated by diminishing fuel consumption. Thus, currently, different strategies are proposed to get this goal; thermal management improvement [2,3], indicated cycle optimization [4,5], in-cylinder heat transfer (HT) reduction [6,7,8], engine friction and auxiliaries losses reduction [9,10] or new combustion modes [11,12,13] among others. In the present work, the research effort has been focused on obtaining an engine setting combination, which leads to a heat transfer reduction with a combustion process improvement and therefore a better engine thermal efficiency.…”

An assessment of the dual-mode reactivity controlled compression ignition/conventional diesel combustion capabilities in a EURO VI medium-duty diesel engine fueled with an intermediate ethanol-gasoline blend and biodiesel

“…In this case, it was found that a bathtub style piston with low surface area allowed a 2-4% absolute increase in gross indicated efficiency, which was attributed to both combustion efficiency and heat transfer improvement [22]. Some other geometries aimed at reducing the heat transfer losses were also tested [23], confirming that the best strategy to increase the efficiency of RCCI concept is by reducing the in-cylinder area-to-volume ratio [24]. However, these studies showed that an excessive shallow bowl combined with single injection strategies can result in unacceptable soot emissions when trying to extend the RCCI concept up to high loads [25].…”

Modeling for Design Optimization of Piston Crown Geometry Through Structural Strength and Lubrication Performance Correlation Analysis

“…To avoid such possibility of rapid wear, micro conjunctions are created intentionally by engraving the ring or liner surface by creating small pools of lubricant (Ryk et al, 2002). Benajes et al (2016) studied the effect of bowl geometry on combustion losses at different load.…”