The Effect of Displacement on Air-Diluted Multi-Cylinder HCCI Engine Performance

Abstract

The main benefit of HCCI engines compared to SI engines is improved fuel economy. The drawback is the diluted combustion with a substantially smaller operating range if not some kind of supercharging is used. The reasons for the higher brake efficiency in HCCI engines can be summarized in lower pumping losses and higher thermodynamic efficiency, due to higher compression ratio and higher ratio of specific heats if air is used as dilution. In the low load operating range, where HCCI today is mainly used, other parameters as friction losses, and cooling losses have a large impact on the achieved brake efficiency.To initiate the auto ignition of the in-cylinder charge a certain temperature and pressure have to be reached for a specific fuel. In an engine with high in-cylinder cooling losses the initial charge temperature before compression has to be higher than on an engine with less heat transfer. The heat transfer to the combustion chamber walls is affected by parameters such as area-to-volume ratio and in-cylinder gas motion, i.e. turbulence.In this paper the performance of three multi-cylinder HCCI engines with different displacements are compared. The engines are a five-cylinder 1.6dm 3 VCR engine, a four-cylinder 2.0dm 3 engine, and a six-cylinder 11.7dm 3 truck engine. All engines are port fuel injected and run with a RON91/MON82 gasoline. Combustion phasing is mainly controlled with inlet air temperature. The engines have about the same indicated efficiency but different brake efficiency. The truck engine has 32.3% brake efficiency at 2bar BMEP, followed by the 2.0dm 3 engine with 29.8%, and the 1.6dm 3 VCR engine with only 24.4%.

The Effect of Intake Temperature in a Turbocharged Multi Cylinder Engine operating in HCCI mode

“…Normally when the NOx level is increased above a set limit [16] the lambda level is used to operate the engine stoichiometric on cylinder to cylinder basis. The engine total efficiency can be divided into fractions [21] as seen in Figure 19. The combustion efficiency is defined as the relationship between heat released (Q hr MEP) and normalized fuel energy/ cycle (FuelMEP).…”

Investigation and Comparison of Residual Gas Enhanced HCCI using Trapping (NVO HCCI) or Rebreathing of Residual Gases

“…The higher compression ratio is expected to give higher thermodynamic efficiencies but lower combustion efficiencies due to increased fuel mass in crevices. The HCCI displacement study by Hyvönen et al [7], also included a comparison between two SI cases, run on the same base engine with 0.5 dm 3 cylinder displacement, with high (18:1) and standard (9.5:1) compression ratio. The high compression ratio SI case had highest net indicated efficiency due to higher thermodynamic efficiency.…”

“…Hyvönen et al [7] did a comparison with three multi-cylinder HCCI engines run on U.S. unleaded regular gasoline with different displacements and heated inlet air to control combustion phasing. All the HCCI cases, independent of engine size had about 40 % net indicated efficiency at 2 bar BMEP.…”

Double Compression Expansion Engine Concepts: A Path to High Efficiency

“…Low temperature combustion (LTC) concepts are a way to improve thermodynamic efficiency. In 2006, experimental work done by Hyvönen et al for a Homogenous Charge Compression Ignition (HCCI) engine reached a thermodynamic efficiency of 49% [17]. However, due to poor combustion, gas exchange and mechanical efficiencies, brake efficiency reached merely 43%, which is not better compared to a current CI engine.…”