Clean Diesel Combustion by Means of the HCPC Concept

Abstract

Homogeneous-charge, compression-ignition (HCCI) combustion is triggered by spontaneous ignition in dilute homogeneous mixtures. The combustion rate must be reduced by suitable solutions such as high rates of Exhaust Gas Recirculation (EGR) and/or lean mixtures. HCCI is considered a very effective way to reduce engine pollutant emissions, however only a few HCCI engines have entered into production. HCCI combustion currently cannot be extended to the whole engine operating range, especially to high loads, since the use of EGR displaces air from the cylinder, limiting engine mean effective pressure, thus the engine must be able to operate also in conventional mode. This paper concerns a study of an innovative concept to control HCCI combustion in diesel-fuelled engines. The concept consists in forming a pre-compressed homogeneous charge outside the cylinder and gradually admitting it into the cylinder during the combustion process. In this way, combustion can be controlled by the transfer flow rate and high pressure rise rates, typical of standard HCCI combustion, can be avoided. This new combustion concept was called Homogenous Charge Progressive Combustion (HCPC). The paper illustrates a CFD analysis focused on improving efficiency and reducing pollutant emissions at medium and heavy load. Different geometries of the transfer duct were considered. Results show negligible soot emission up to equivalence ratios around 0.85, with indicated efficiency around 46 %. As well, a moderate level of external cooled EGR allows reducing NOx emissions up to levels that are typical of low-temperature combustion

A review of split-cycle engines

“…The crossover passage is incorporated into the expander. This engine configuration, shown in Figure 30, has been extensively investigated using computational fluid dynamics (CFD) modelling by the University of Pisa [51,52]. The concept, named Split-Cycle Clean Combustion (SCCC), has also been investigated by Caterpillar and the University of Illinois using a one-dimensional model [53,54].…”

“…It was found the concept gives high indicated thermal efficiencies of approximately 46% [51]. The concept also promises to significantly reduce emissions giving both soot and NOx reductions.…”

Homogeneous Charge Compression Ignition (HCCI) Combustion Engine- A Review

“…In this concept, the pre-compressed homogeneous mixture is to be prepared outside the engine cylinder and this mixture is to be inducted gradually into the cylinder during the combustion process. In this way, the combustion can be regulated by the transfer flow rate, and high-pressure-rise rates, which are the characteristic of conventional HCCI combustion, can be avoided [36,37]. In this concept, the negligible soot emission up to equivalence ratios close to 0.85, with indicated efficiency of about 46% has been reported [4].…”

Modeling and Validation of a Split Cycle Clean Combustion Diesel Engine Concept

“…Computational fluid dynamics (CFD) modeling produces more accurate results but limits one's ability to model a large number of configurations due to its large computational overhead that slows down the overall simulation process, thus making CFD models not feasible for this DOE. In order to accurately model an SCCC engine, we first validated our modeling methodology by reproducing results of the CFD based model presented by University of Pisa in Musu et al (2010, "Clean Diesel Combustion by Means of the HCPC Concept," SAE Paper No. 2010-01-1256.…”

“…A two-cylinder variant of the SCCCE is modeled using Caterpillar's one-dimensional modeling software DYNASTY, following the geometric and boundary specifications given by the University of Pisa in their paper by Musu et al (2010, "Clean Diesel Combustion by Means of the HCPC Concept," SAE Paper No. 2010-01-1256.…”