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The HCCI engine could offer low NOx, PM emissions and high efficiency. However the operation region of the HCCI combustion is limited because of the knocking at high load and the misfire at low load. Moreover the HCCI principle lacks direct combustion control and needs a system to control the combustion phasing with high accuracy. Today there exists various ways to control the HCCI combustion, such as Variable Valve Train, Variable Compression Ratio, Inlet Air Heating and Dual Fuels. However such variable mechanisms and Inlet Air Heating tend to be heavy and complex. Dual Fuels method needs two types of fuels and has a challenge in infrastructure. In this study, in order to develop a small and light HCCI engine, a simple HCCI combustion control system is proposed. DME (Di-methyl Ether) is used as the fuel to keep the structure small and light. In this system, the mixing ratio of three gases: stoichiometric pre-mixture, hot EGR gas and cold EGR gas is changed by only throttles.

The characteristics of cycle-to-cycle variations of indicated mean effective pressure (IMEP) with combustion-phasing retard have been investigated experimentally and computationally in an homogeneous charge compression ignition (HCCI) engine using dimethyl ether (DME). The experiments were conducted in a single-cylinder HCCI research engine equipped with an exhaust gas recirculation (EGR) passage for external EGR and a two-stage exhaust cam for rebreathed EGR. To understand the chemical effects of rebreathed EGR, which is assumed to contribute to the autoignition enhancement, the computations were performed with a single-zone model of CHEMKIN using a chemical-kinetic mechanism developed by combining DME mechanism and NOx submechanism.

Homogeneous charge compression ignition (HCCI) combustion requires high EGR rate and high intake temperature. HCCI combustion has not yet been made to operate at conditions other than low speed and low load in a four-stroke engine. Two stroke engine, however, have produced reasonable power in the HCCI combustion or active thermo-atmosphere combustion (ATAC) mode. In this paper, the nature of ATAC is discussed by spectroscopic observation to determine why the ATAC (under favorable condition) produces very low cyclic irregularity and low NO emission. ATAC low heat rejection engine and ATAC with alternative fuels are discussed.

The possibility of turbocharging into a natural gas homogeneous charge compression ignition (HCCI) engine is investigated experimentally and by simulation. Experiments are performed using a four-cylinder naturally aspirated engine fitted with an external supercharger and a butterfly valve for back pressure control to simulate a turbocharger with efficiency of 0.64. Based on the test results, the performance and emission characteristics are studied in detail through numerical one-dimensional cycle simulations. The results indicate that the thermal efficiency can be improved by raising the engine compression ratio and lowering the turbocharging pressure. At an engine compression ratio of 21 and turbocharging pressure of 1.9 bar, the brake thermal efficiency reaches 0.43, with NOx emissions of only 10 ppm or less.

The Homogeneous Charge Compression Ignition (HCCI) engine is possible to achieve high thermal efficiency and low emissions. One of the main challenges with HCCI engines is structuring the systems to control combustion phasing, crank angle of 50% heat release (CA50), for keeping high thermal efficiency and avoiding an excessive rate of pressure rise which causes knocking, when operating conditions vary. Though some HCCI combustion control systems, for example Variable Valve Timing System and Variable Compression Ratio System, have been suggested, these control systems are complex and heavy. In this study, for the development of a lightweight and small-sized generator HCCI engine fuelled with Dimethyl Ether (DME) which is low-emission and easy to autoignite, a simple HCCI combustion control system is suggested, and the control system is evaluated experimentally.

ATAC is “bulk-like” and/or “non-propagating” combustion caused by compression autoignition of premixture, and it is stable even in the lean region. And ATAC engine is expected to be an engine using alternative fuels which are difficult to apply to usual engines because of their low cetane number. In this study, a two-stroke ATAC engine test was carried out to evaluate an adaptability of alternative fuels for lean burn. Methanol, ethanol, DME, methane and propane were used as the test fuels, and the influence of fuel characteristics on autoignition timing, combustion duration and autoignition temperature were investigated in the lean region. Using oxygenated fuels, the lean limit of ATAC operation region shifts to lean side. ATAC autoignition temperature is not depend on equivalence ratio, delivery ratio and engine speed, and it is only decided by the kind of fuel. The order of the ATAC autoignition temperature is methanol, ethanol, DME, gasoline from lower side.

The operating range is restricted by knocking and misfiring in a homogeneous charge compression ignition (HCCI) engine. In an HCCI engine, the autoignition does not always mean the high combustion efficiency because the operating range to achieve high combustion efficiency is very narrowly restricted by knocking and high THC, CO emissions. In this study, we have investigated the operating conditions to achieve high combustion efficiency and low CO emission in a four-stroke HCCI engine using experimental analysis and elementary reactions calculation. It is shown that the combustion efficiency reaches higher than 90%, and the CO emission can be reduced considerably when the in-cylinder maximum gas temperature is over 1600K.

ATAC (Active Thermo-Atmosphere Combustion) is autoignition combustion in two stroke engines, which occurs by diluting trapped Fuel-Air mixture with residual gas to maintain a high temperature at low load operation. In this study, two-stroke ATAC engine testing was carried out to obtain fundamental knowledge for controlling the autoignition and combustion characteristics in this premixed charge compression-ignition combustion engine. The influences of delivery ratio, equivalence ratio and enginespeed (i.e. compression speed) on autoignition timing, autoignition temperature and combustion duration were investigated. It was found that the ATAC autoignition temperature and combustion duration did not depend on the delivery ratio and equivalence ratio, but were determined by the individual fuel characteristics. Increasing the compression speed reduced the ATAC autoignition temperature a little.

The research shows the experimental results for a free piston linear engine according to operation conditions of the linear engine and the structure of linear generator for generating electric power. The powerpack used in this paper consists of the two-stroke free piston linear engine, linear generators and air compressors. Each parameter of fuel input heat, equivalence ratio, spark timing delay, electrical resistance and air gap length were set up to identify the combustion characteristics and to examine the performance of linear engine. The linear engine was fueled with propane. In the course of all linear engine operations, intake air was inputted under the wide open throttle state. Air and fuel mass flow rate were varied by using mass flow controller and these were premixed by pre-mixing device. Subsequently, pre-mixture was directly supplied into each cylinder.

Recently, a potentiality of Dedicated EGR (D-EGR) concept SI engine has been studied. This concept engine had four cylinders and operated with exhaust gas supplied from the single cylinder to the intake manifold. Compared with conventional SI engines, it was able to increase thermal efficiency and decrease CO, HC, and NOx emission by the high D-EGR ratio 0.25. In this study, numerical analysis of a SI engine with D-EGR system with various D-EGR ratios was conducted for detailed understanding the potentiality of this concept in terms of thermal efficiency and NOx emission. #1 cylinder of assumed engine was used as D-EGR cylinder that equivalence ratio varied from 0.6 to 3.4. Entire exhaust gas from #1 cylinder was recirculated to the other cylinders. The other cylinders run with this exhaust gas and new premixed air and fuel with various equivalence ratios from 0.6-1.0.

This study has been computationally investigated how the DME autoignition reactivity is affected by EGR and intake-pressure boost over various engine speed. CHEMKIN-PRO was used as a solver and chemical-kinetics mechanism for DME was utilized from Curran's model. We examined first the influence of EGR addition on autoignition reactivity using contribution matrix. Investigations concentrate on the HCCI combustion of DME at wide ranges of engine speeds and intake-pressure boost with EGR rates and their effects on variations of autoignition timings, combustion durations in two-stage combustion process in-detail including reaction rates of dominant reactions involved in autoignition process. The results show that EGR addition increases the combustion duration by lowering reaction rates.