The Modeling And Experimental Study Of Homogeneous Charge Compression Ignition (HCCI) In IC Engine

Homogeneous charge compression ignition (HCCI) combustion is the process in which a homogeneous mixture is auto-ignited through compression. This combustion process has the potential to significantly reduce NOx and particulate emissions, while achieving high thermal efficiency and having the capability of operating with a variety of fuels. To a degree, the HCCI combustion process is able to combine the best features of a spark ignition (SI) engine using gasoline fuel and a diesel engine using diesel fuel. Similar to an SI engine, the fuel and air are mixed to obtain a homogeneous mixture, which can eliminate fuel-rich diffusion combustion and can thus dramatically reduce the particulate emissions that are usually associated with conventional diesel combustion processes. With the ignition process similar to that of a diesel engine, the HCCI engine undergoes an auto-ignition process through the entire combustion chamber that can eliminate the high-temperature flames of conventional engine combustion. Therefore the NOx emissions from HCCI engines can be very low when compared to those of conventional engine combustion processes. Furthermore, the unthrottled operation of the gasoline HCCI engine is possible at a very low equivalence ratio and at a high rate of external exhaust gas recirculation (EGR) without misfire, thus yielding a high thermal efficiency with a very low cycle-by-cycle combustion variation. Therefore the HCCI engine is an attractive technology that can ostensibly provide diesel-like fuel efficiency and very low engine-out emissions, which may allow emissions compliance to occur without relying on lean after treatment systems.Over the last several years, numerous studies have been reported to explore the potential of this technology and many innovative strategies for mixture preparation, combustion control, load extension, and emissions reduction have been proposed and developed.This thesis covers a wide spectrum of key research and development issues in the rapidly progressing area of HCCI engines. Firstly a historical review of HCCI combustion research and development is provided. Future technology directions and R&D needs are also outlined. The primary reference fuel, n-heptane and isooctane, were blended as the model fuel to predict the auto-ignition timing of gasoline and diesel blended fuel HCCI, because real gasoline and diesel is a complex mixture of many components.The auto-ignition and combustion mechanism of hydrogen/natural gas were investigated by using a zero dimensional thermodynamic model coupled with a detailed chemical kinetics mode.A nine-zone combustion model have been developed, validated and used in this thesis. The combustion models were connected to a cycle simulation code, which can be applied to simulations of the complete HCCI engine cycle, i.e. including the gas exchange processes which are important for HCCI mixture preparation.Experiments had been conducted with a single cylinder engine operated with moderate compression ratios (10.4 and 15) and using two modes of HCCI control, i.e. intake heating and NVO (Negative Valve Overlap) to prove the promative effect of diesel fuel on gasoline HCCI.Hydrogen addition through exhaust gas fuel reforming was also examined as a possible method of reducing intake temperature requirements for natural gas HCCI combustion, which normally requires higher intake temperatures.