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Homogeneous Charge Compression Ignition (HCCI) is good method to be higher efficiency and to reduce NOx emission and particular matter together than conventional SI combustion engine. But HCCI depends on chemical reaction of fuel and air mixture. So controlling of ignition timing is difficult, and HCCI is high THC and CO emissions because temperature can't reach the enough temperature to reduce those. In this study, we investigated factor for auto ignition timing and combustion completion on n-Butane/Air mixture by a two-stroke HCCI engine. Auto Ignition temperature are known to be decided by fuel(1), for n-Butane, the temperature was 1150±30K. And as we researched combustion completion from In-cylinder gas temperature, increasing In-cylinder gas temperature caused high combustion efficiency and low THC, CO emissions.

This study computationally investigates the combined effects of EGR and boost pressure on HCCI autoignition using iso-octane, PRF50 and n-heptane. The computations were conducted using the single-zone model of CHEMKIN included in CHEMKIN-PRO with detailed chemical-kinetics mechanisms for iso-octane, PRF and n-heptane from Lawrence Livermore National Laboratory (LLNL). To better reproduce the state of EGR addition in real engine, the EGR composition is determined after several combustion cycles under the constant amount of fuel. All data points were acquired with a CA50 of 5°CA aTDC by adjusting initial temperature to remove the effect of combustion phasing, which can influence on HCCI autoignition from any effect of the EGR and boost pressure themselves. The results show that EGR increases the burn duration and reduces the maximum pressure-rise rate with lower peak of maximum heat-release rates for all fuels even for a boost pressure, which accelerates a HCCI autoignition propensity.

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.

To adhere to stringent environmental regulations, SI (spark ignition) engines are required to achieve higher thermal efficiency. In recent years, EGR (exhaust gas recirculation) systems and lean-burn operation has been recognized as key technologies. Under such operating conditions, reducing CCV (cycle-to-cycle variation) in combustion is critical to the enhancement of overall engine performance. Flow-field CCV is one of the considerable factors affecting combustion in engines. Conventionally, in research on flow fields in SI engines, the ensemble average is used to separate the measured velocity field into a mean component and a fluctuation component, the latter of which contains a CCV component and a turbulent component. To extract the CCV of the flow field, previous studies employed spatial filter, temporal filter, and POD (proper orthogonal decomposition) methods.

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.

Problem of HCCI combustion is knocking due to a steep heat release by the ignition that is occurred in each local area at the same time. It is considered that dispersion of auto-ignition timing at each local area in the combustion chamber is necessary to prevent this problem. One of technique of this solution is to make thermal stratification. It could be made by using two-stage ignition fuel, which has large heat release at low temperature reaction. Dispersion of fuel concentration leads to difference of temperature histories while combustion phasing is dispersed at each local area. Also, EGR gas stratification could make difference of temperature histories at each local area because of that of the characteristics. This study examines the effect of mixing stratification by stratifying the charge of fuel and CO2. A single-cylinder engine equipped with optical access was used in experiments, and numerical analysis was executed.

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.

The Dual-Fuel (DF) combustion is a promising technology for efficient, low NOx and low exhaust particulate matter (PM) engine operation. To achieve equivalent performance to a DF engine with only the use of conventional liquid fuel, this study proposes the implementation of an on-board fuel reformation process by piston compression. For concept verification, DF combustion tests with representative reformed gas components were conducted. Based on the results, the controllability of the reformed gas composition by variations in the operating conditions of the reformer cylinder were discussed.

Spark-assisted diesel engines operated with alcohol fuels usually display misfiring or knocking problems. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a swirl chamber diesel engine with a multi-spark ignitor. In the experiments, cycle-to-cycle combustion variations and the degree of knocking were investigated by changing engine parameters over a wide operating range. The results of the investigations showed that stable ignition and smooth combustion is achieved when a flammable mixture is formed in the vicinity of the spark plug when only a small amount of the injected fuel has evaporated. By optimizing the design factors, operation with high efficiency and low exhaust emissions was achieved.

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.

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.

Theoretically, homogeneous charge compression engines (HCCI) are able to grant a high thermal efficiency, as well as a low NOx and particulate emissions. This ability is mainly due to the combustion process, which, contrary to both Diesel and Gasoline engine, is homogeneous in time and space within the combustion chamber. But despite these advantages, the engine operating condition is limited by the narrow boundaries of misfire at low load and knocking at high load. For that matter, one of the numerous ways of overcoming knocking is to deliberately create fuel inhomogeneities within the combustion chamber, since it has proved to lengthen combustion duration and to drastically reduce maximum pressure rise rate (PRR). Nevertheless, though the global effects of fuel inhomogeneities on PRR have been studied, we lack information that explains this phenomenon.

HCCI (Homogeneous Charge Compression Ignition) engine is able to achieve low NOx and particulate emissions as well as high efficiency. However, its operation range is limited by the knocking at high load, which is the consequence of excessively rapid pressure rises. It has been suggested that making thermal or fuel inhomogeneities can be used to solve this problem, since these inhomogeneities have proved to create different auto-ignition timing zones. It has also been suggested that EGR (Exhaust Gas Recirculation) has a potential to reduce pressure rise rate. But according to a past report, it was concluded that under the same fueling ratio and CA50 with different initial temperature and EGR ratio, the maximum PRR is almost constant. The purpose of this study is to investigate the fundamental effects of EGR. First, I considered EGR homogeneous charge case. In this case, the effects of EGR and its components like CO₂, H₂O or N₂ on HCCI combustion process is argued.

Thermal and mixing stratifications have been thought as one of the ways to avoid an excessive pressure rise on HCCI combustion. The purpose of this research is to investigate the potential of thermal and mixing stratifications for reducing PRR (Pressure Rise Rate) on HCCI combustion. The pre-mixture with thermal and mixing stratifications is charged in RCM (Rapid Compression Machine). After that, the pre-mixture is compressed and in that process, in-cylinder gas pressure and chemiluminescence images are obtained and analyzed. Furthermore, experimental results are compared with the computational results calculated by using multi-zone model for analyzing these mechanisms.

To monitor emission-related components/systems and to evaluate the presence of malfunctioning or failures that can affect emissions, current diesel engine regulations require the use of on-board diagnostics (OBD). For diesel particulate filters (DPF), the pressure drop across the DPF is monitored by the OBD as the pressure drop is approximately linear related to the soot mass deposited in a filter. However, sudden acceleration may cause a sudden decrease in DPF pressure drop under cold start conditions. This appears to be caused by water that has condensed in the exhaust pipe, but no detailed mechanism for this decrease has been established. The present study developed an experimental apparatus that reproduces rapid increases of the exhaust gas flow under cold start conditions and enables independent control of the amount of water as well as the gas flow rate supplied to the DPF.

This work has been investigated the potential of in-cylinder EGR stratification for reducing the pressure rise rate of DME HCCI engines, and the coupling of both thermal stratification and fuel stratification. The numerical analyses were done by using five-zone version of CHEMKIN-II kinetics rate code, and kinetic mechanics for DME. The effects of inert components were used for the presence of EGR in calculation. Three cases of EGR stratification were tested on both thermal stratification and fuel stratification at the fixed initial temperature, pressure and fueling rate at BDC. In order to explore the appropriate stratification of EGR, EGR width was employed from zero to thirty percent. Firstly, EGR homogeneity case which means EGR width zero was examined. Secondly, EGR is located densely in hotter zone for combining with thermal stratification or in richer zone for a combination with fuel stratification. Lastly, the case was judged inversely with the second case.

The characteristics of auto-ignition of DME/Air mixture in Homogeneous Charge Compression Ignition (HCCI) engine were investigated by numerical calculation with elementary reactions and experiment. Calculations were carried out using Di-Methyl Ether (DME) elementary reactions at 0 dimension and adiabatic condition. DME is paid attention as the alternative fuel of next generation because of its possibility to take the place of conventional fossil fuels. DME has good characteristics of auto-ignition and combustion with low flame temperature, and makes no soot because of its molecular structure. In autoignition process, DME shows two-stage combustion, heat release with low temperature reaction (LTR) and high temperature reaction (HTR). This characteristic is similar to higher hydrocarbons such as gasoline in auto-ignition process. In this study, analysis of HCCI combustion of DME/Air mixture was carried out by using numerical calculation and comparing with experimental results.

Soot emission from diesel engines generally increases with shorter ignition lags. However, the detailed process and mechanism of this phenomenon has not been well understood. This investigation attempts to observe and analyze the in-chamber soot formation process at various ignition lags by high-speed photography of the direct flame images and laser shadowgraphs as well as the laser light extinction. In the experiment, the separation of soot concentration from the soot-fuel mixture concentration was established by subtracting the laser light extinction intensity through a non-firing chamber from that through a firing chamber. It was found that the soot concentration in the swirl chamber reached a maximum value immediately after the start of combustion, and then decreased rapidly. With shorter ignition lags, the maximum and final soot concentrations in the chamber increased.

For the reduction of greenhouse gas emission in the transportation sector, various countermeasures against CO₂ emission have been taken. The eco-driving has been paid attention because of its immediate effect on the CO₂ reduction. Eco-driving is defined as a driving method with various driving techniques to save fuel economy. The eco-driving method has been promoted to the common drivers as well as the drivers of carriers. Additionally, there are many researches about improvement of fuel efficiency and CO₂ reduction. However, the eco-driving will have the reduction effect of CO₂ emission, the influence of the eco-driving on air pollutant emission such as NOx is not yet clear. In this study, the effect of the eco-driving on real-world emission has been analyzed using the diesel freight vehicle with the on-board measurement system.

This study makes use of the detailed mechanisms of n-heptane combustion, from gas reactions to soot particle formation and oxidation, and a two-stage model based on the CHEMKIN reactor network is developed and used to investigate the trade-off between soot and NOx emissions. The effects of the equivalence ratio, EGR, ambient pressure and temperature, and initial particle diameter are observed for various residence times. The results show that high rates of NOx formation are unavoidable under conditions where high reduction rates of soot particles are obtained. This suggests that suppression of the amount of soot during the formation stage is essential for simultaneous reductions in engine-out soot and NOx emissions.