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Lean burn is one method for improving thermal efficiency in spark ignition (SI) engines. Suppression of knocking provides higher thermal efficiency, and ethanol blending is considered an effective way to suppress knocking due to its high octane and high latent heat of evaporation. We investigate the effect of ethanol blending on knocking in an SI engine under lean operating conditions. The Livengood-Wu (LW) integral was performed based on ignition delay duration estimated from a zero-dimensional detailed chemical reaction calculation with pressure and temperature histories. Knocking was suppressed and thermal efficiency increased with ethanol-gasoline blending fuel, even at 0.5 equivalence ratio. Decrease in unburned gas temperature by latent heat of evaporation had a comparable influence on knocking suppression, which was supported by LW integral analysis.

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.

It has been shown that lean burn is effective for improving the thermal efficiency of gasoline SI engines. This happens because the reduction of heat loss by decrease of flame temperature. On the other hand, the fuel dilution of the premixed gas makes the combustion speed low, and cycle-to-cycle variations of combustion are increased by excessive dilution, it is difficult to increase the thermal efficiency of the gasoline SI engine. Influence of ignition by spark discharge is considered as a factor of combustion variation, and it is necessary to understand the effects of spark discharge characteristics on the lean combustion process. Spark discharge in the SI engines supplies energy to the premixed-gas via a discharge channel in the spark plug gap which ignites the premixed-gas. The discharge channel is elongated by in-cylinder gas flow and its behavior varies in each cycles.

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.

This study tried to find a potential of dedicated EGR (d-EGR) system added to the four-cylinder spark ignition (SI) engine to decrease heat loss (Qheatloss) and improve thermal efficiency (ηth). Test fuels were chosen by methane and propane. PREMIX code in CHEMKIN-PRO was employed to calculate laminar burning velocity (SL) and flame temperature (Tf). Wiebe function and Wocshni's heat transfer coefficient were considered to calculate ηth. The results show that the d-EGR system increased ηth and it was higher than that of stoichiometric combustion of conventional SI engines due to the low Tf and fast SL.

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.

A simulation study was conducted to examine the transition from SI combustion to HCCI combustion in a two-stroke free piston engine fuelled with propane. Operation of the free piston engine was simulated based on the combination of three mathematical models including a dynamic model, a linear alternator model and a thermodynamic model. The dynamic model included an analysis of the piston motion, based on Newton's second law. The linear alternator model included an analysis of electromagnetic force, which was considered to be a resistance force for the piston motion. The thermodynamic model was used to analysis thermodynamic processes in the engine cycle, including scavenging, compression, combustion, and expansion processes. Therein, the scavenging process was assumed to be a perfect process. These mathematical models were combined and solved by a program written in Fortran.

This study experimentally investigates the control system and the algorithm after constructing a HCCI combustion control system for the development of a small HCCI engine fuelled with Dimethyl Ether (DME). This system can control four throttles for the mixing ratio of three gases of in-cylinder (stoichiometric pre-mixture, hot EGR gas and cold EGR gas). At first, the combustion behavior for combustion phasing retarded operation with cold and hot EGR was examined. Then, the potential of model-based and feed back control for HCCI combustion with change of the demand of IMEP was investigated. In the end, the limit of combustion-phasing retard for IMEP and PRR was explored. Results shows that to get high IMEP with acceptable PRR and low coefficient of variation of IMEP, crank angle of 50% heat release (CA50) should be controlled at constant phasing in the expansion stroke. CA50 can be controlled by changing the ratio of pre-mixture, hot EGR gas and cold EGR gas with throttles.

CNG/diesel dual-fuel engine is using CNG as a main fuel, and injects diesel only a little as an ignition priming. In this study, remodeling an existing diesel engine into dual-fuel engine that can inject diesel with high pressure by CRDI (Common Rail Direct Injection), and injecting CNG at intake port for premixing. The results show that CNG/diesel dual-fuel engine satisfied coordinate torque and power with conventional diesel engine. And CNG alternation rate is over 89% in all operating ranges of CNG/diesel dual-fuel engine. PM emission is lower 94% than diesel engine, but NOx emission is higher than diesel engine. The output of dual fuel mode is 95% by the diesel mode. At this time, amount of CO₂ and PM are decreased while CO, NOx, and THC are increased. In NEDC mode, exhaust gases except NOx are decreased.

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.

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.

This work experimentally investigates how the dwell time between pilot injection and main injection influences combustion characteristics and emissions (NOx, CO, THC and Smoke) in a single-cylinder DI diesel engine. Additionally, results from diesel injection are compared with those shown in dimethyl ether (DME) injection under the identical injection strategy to demonstrate the sensitivity of the combustion characteristics and emissions to changes of the fuel type. Two fuel injection systems are applied for this experiment due to the differences of fuel characteristic with regard to physical and chemical properties. The injection strategy is accomplished by varying the dwell time (10°CA, 16°CA and 22°CA) between injections at five main injection timings (-4°CA aTDC, -2°CA aTDC, TDC, 2°CA aTDC and 4°CA aTDC). It was found that pilot injection offers good potential to lower the heat-release rate with reduced pressure traces regardless of the dwell time between injections and fuel type.

Nitrogen oxides, collectively called NOx, from diesel vehicles are considered to be accumulated by particular area of roadsides, so-called "Hot-spot," and result in harmful influence to pedestrians and residents by roadsides. Japanese regulations over emissions of diesel vehicles have been tightened year by year and adopting regulations, emissions in mode test on chassis dynamometer or engine dynamometer have reduced. In this research, it was investigated the effect of introduce of transient mode test, Japanese JE05 mode, to NOx emission in real world and to roadside NOx pollution by road test using on-board measurement system. As test vehicles, 2 ton diesel vehicle which is adopted for Long Term Regulation (steady-state mode test, Diesel 31 mode test, 1998) and 3 ton diesel vehicle adopted for New Long Term Regulation (transient mode test, Japanese JE05 mode, 2005) with on-board measurement system was used.

Delaying CA50(Crank Angle of 50% Heat Release) of the HCCI engine to expansion stroke can lead to high indicated thermal efficiency as well as the avoidance of knocking. However, this method could induce the problem of cycle variability. In this study, the cycle-to-cycle variation of a HCCI engine fueled with DME was investigated. Experimental parameters of each cycle, such as in-cylinder temperature, pressure and gas flow rate, were recorded by fast response system, and analyzed consequently. Moreover, the interdependency between the combustion and the performance parameters were evaluated.

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.

A significant drawback to HCCI engines is the knocking caused by rapid increases in pressure. Such knocking limits the capacity for high-load operation. To solve this problem, thermal stratification in the combustion chamber has been suggested as possible solution. Thermal stratification has the potential to reduce the maximum value of the rate of pressure increase combustion by affecting the local combustion start time and extending the duration of combustion. The purpose of this study was to experimentally obtain fundamental knowledge about the effect of thermal stratification on the HCCI combustion process. Experiments were conducted in a rapid compression machine (RCM) equipped with a quartz window to provide optical access to the combustion chamber. The machine was fueled with DME, n-Butane, n-Heptane and iso-Octane, all of which are currently being investigated as alternative fuels and have different low temperature characteristics.

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.

The purpose of this study was to gain a better understanding of the effects of in-cylinder gas temperature stratification on reducing the pressure-rise rate in HCCI combustion. HCCI combustion was investigated using an optically accessible engine and direct visualization of the combustion chemiluminescence. The engine was fueled with Di-Methyl Ether. Computational work was conducted on the gas compression and expansion strokes in HCCI engine with simple 0-dimensinal multi-zones model. When fuel inhomogeneous charging in experiment, maximum heat release rate decreased. Combustion duration got longer. Maximum pressure-rise rate decreased. Chemiluminescence, of which transition was identified from the side of intake valve to the side of exhaust valve, was observed. It is need for total moderate heat release to get local moderate combustion with not overall but continuous combustion in chamber.

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.