Published papers

The purpose of this study was to compare the spray characteristics, the combustion characteristics and the emissions (nitrogen oxides, carbon monoxide, hydrocarbon and smoke) of typical fuels (100% diesel and 100% dimethyl ether) and diesel–dimethyl ether fuel blends in a constant-volume chamber and a single-cylinder direct-injection diesel engine. The spray characteristics were investigated by varying the ambient pressure and the fuel injection pressure using a commonrail fuel injection system with various fuel mixture ratios. The spray characteristic research parameters were the spray shape, the penetration length and the spray angle at the seven-hole injector. Common types of injector were used (Bosch). Two types of fuel blended by mass fraction were employed. Typical fuels (100% diesel and 100% dimethyl ether) and fuel blends with diesel:dimethyl ether mixture ratios of 95:5 and 90:10 were used. The injection pressure was fixed at 70 MPa while the ambient pressure was varied (0 MPa, 2.5 MPa and 5 MPa). The combustion experiments were conducted in a single-cylinder engine equipped with a common rail. The injection pressure was 700 bar at 1200 r/min. The amount of injected fuel was adjusted to obtain a fixed input calorific value of 972.2 J/cycle in order to make a comparison between the fuel types. The results showed that the injection quantity was greater with diesel fuel but not for dimethyl ether fuel and for the fuel blend with the higher mixing ratio. The spray penetration length increased with increasing ambient pressure for diesel but decreased for dimethyl ether with a larger spray angle. The ignition delay and the heat release rate decreased with increasing dimethyl ether which led to a higher indicated mean effective pressure and higher thermal efficiency because there was less negative work in the expansion. The total hydrocarbon emissions and the carbon monoxide emissions decreased with increasing dimethyl ether, but the nitrogen oxide emissions generated were greater owing to the increased combustion temperature.

Object of this study is to realize improving thermal efficiency and emission reduction with low temperature combustion. EGR is a solution to low temperature combustion, however it occurs burning velocity decrease. To prevent this phenomenon, Dedicated EGR was adjusted to SI engine run by natural gas. The entire exhaust gas of a single cylinder operated by the equivalence ratio varied from lean to rich was recirculated to the other cylinders. Due to H2 and CO included in EGR, slowed burning velocity problem was overcome with increasing degree of constant volume, thus thermal efficiency could be improved.

This study experimentally investigates the effects of the combustion phasing on the homogeneous charge compression ignition (HCCI) combustion, and implements a closed-loop control of HCCI combustion to reduce pressure-rise rate (PRR) with combustion-phasing retard. The experiments were conducted using dimethyl ether (DME) in a single-cylinder HCCI research engine equipped with an exhaust gas recirculation (EGR) loop for external EGR and a two-stage exhaust cam for rebreathed EGR. The results show that a maximum PRR (PRRmax) and a maximum in-cylinder charge temperature decreases with combustionphasing retard. However, excessive combustion-phasing retard leads to unacceptable coefficient of variation (COV) of CA50 and IMEP with partial-burn and/or misfire cycles. To dampen increasing cycleto- cycle variations around the limit of combustion-phasing retard, the closed-loop control of HCCI combustion was implemented using three feedback variables. Finally, stable stoichiometric HCCI operation could be achieved with extensive combustion-phasing retard while maintaining acceptable PRRmax with the higher level of IMEP.

An investigation was conducted to examine the effects of key parameters such as intake temperature, equivalence ratio, engine load, intake pressure, spark timing and spring stiffness on the transition from SI combustion to HCCI combustion in a two-stroke free piston linear engine. 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. These mathematical models were combined and solved by a program written in Fortran. To validate the mathematical models, the simulation results were compared with experimental data in the SI mode. For the transition from SI combustion to HCCI combustion, the simulation results show that if the equivalence ratio is decreased, the intake temperature and engine load should be increased to get a successful SI-HCCI transition. However, the simulation results also show that the in-cylinder pressure is decreased, while the peak in-cylinder temperature in HCCI mode is increased significantly if the intake temperature is increased so much. Beside the successful SI-HCCI transition, the increase of intake pressure from Pin = 1.1 bar to Pin = 1.6 bar is one of solutions to reduce peak in-cylinder temperature in HCCI mode. However, the simulation results also indicate that if the intake pressure is increased so much (Pin = 1.6 bar), the engine knocking problem is occurred. Adjusting spring stiffness from k = 2.9 N/mm to k = 14.7 N/mm is also considered one of useful solutions for reducing the peak in-cylinder temperature in HCCI mode as well as avoiding engine knock. Besides, the change of spark timing is suggested as a benefic method to help the control of the SI-HCCI transition to be more convenient. To get a successful SI-HCCI transition with reducing of peak temperature in HCCI mode as well as avoiding engine knock, the simulation results show that the engine should be operated with following conditions: equivalence ratio / = 0.7, engine load RL = 180 X, intake temperature Tin = 400 K, intake pressure Pin = 1.2 bar, spark timing in SI mode xig = 3 mm and spring stiffness k = 14.7 N/mm.

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. In the control system, the means of controlling gas temperature at inlet valve closure (IVC) is focused on to control CA50 as the specific autoignition temperature of a fuel is constant in HCCI combustion. The amount of premixture of air and fuel at stoichiometric ratio necessary to achieve load is fixed, and gas temperature at IVC is controlled by changing the mixing ratio of hot (internal) EGR gas and cold (external) EGR gas. And also cold EGR gas plays a role in the avoidance of a very rapid combustion reaction speed. The exhaust cam has two stages to use hot EGR gas, and exhaust gas is cooled through the heat exchanger to use cold EGR gas. The mixing ratio of three gases, stoichiometric premixture, hot EGR gas and cold EGR gas, is controlled by four throttles placed in the flow path of these gases.

The purpose of this study is to investigate experimentally the effect of fuel stratification on HCCI combustion, using DME. In addition to pressure measurement, the chemiluminescence image in HCCI combustion is used a means of visualizing the charge stratification and evaluating local combustion characters. It was found that fuel stratified charge in DME reduced the maximum pressure rise rate during HCCI combustion. By fuel-stratified charge, the peak time of chemiluminescence intensity was dispersed, comparing to fuel homogeneous charge. Therefore, distribution of equivalence ratio is generated, and this distribution makes the peak time of RHR in each local area dispersed.

HCCI engine has the problem of limited operating region. To solve this problem, the method of mixing the fuels with different reactivities was paid attention. In this study, the expansion of the operating region of HCCI engine was tried by using double componential fuels. In this report, when DME, n-butane, hydrogen or carbon monoxide was mixed with methane, the effects of the mixing ratios on the oxidation reaction processes of pre-mixture were investigated by numerical calculations with elementary reactions.

HCCI engine has the problem of limited operating region. To solve this problem, the method of mixing the fuels with different reactivities was paid attention. In this study, the expansion of the operating region of HCCI engine was tried by using double componential fuels. In this report, based on the results of the first report, the combustion experiment by mixing DME or n-butane with methane was carried out. The mixing conditions of fuels to realize both of high output and high thermal efficiency were clarified.

As input heat quantity per cycle greatly affects CA50, the change in input heat quantity per cycle needs to be considered to control CA50 by gas temperature at IVC. In the control system, the measured IMEP has the slow response and vibrates to the IMEP set value. Meanwhile, the CA50 controller shows the good performance in aspects of steady and transient characteristics. Hereafter, the IMEP controller should be improved without reducing the performance of the CA50 controller.

In this paper the diesel in-cylinder control of nitrogen oxide(NOx) and soot formation was tested. Carbon dioxide(CO2) was used as a dilutuent to simulate the exhasut-gas recirculation(EGR) process at ratios of 4.3%, 9.5% and 14.3%, thus making oxygen(O2) concentrations of 20%, 19% and 18% respectively. In addition, three diesel fuels with different T90 distillation temperatures were used, The fuel parameters were isolated from the influence of the aromatics content, sulfer content, and cetane number. A single-cylinder rapid compression machine(RCM) was used to simulate the diesel-tye combustion. The igniton and combustion process of diesel-fuel spray were observed using high-speed direct photography. The flame temperature (an indication of NO formatio) and KL factor (an indication off soot concentration inside the diesel-fuel spray) were analyzed using two-color method. The study demonstrated that with an increase of the CO2 concentration in the intake charge, the maximum flame temperature and the soot formation decrease. Also, when therewas a CO2=4.3% concentration in the intake charge, the results showed no significant influence of the diesl-ffuel T90 distillation temperature on the maximum flame temperature and the soot formation.

Using Methane/DME, Methane/n-Butane or Methane/Hydrogen as the fuels for the HCCI combustion, influences of the fuel composition on the HCCI combustion mechanism were resulted in the numerical calculation with detailed elementary reactions. The effects of ignition timing, the combustion reaction speed and Mixing ratio of fuels were investigated. It was found that 50% heat release timing in the expansion stroke is important for high power operation. And in the HCCI engine combustion tests, it was clear that the high power operation reducing knocking was handled in the condition of the 50% heat release timing in the expansion stroke.

The Homogeneous Charge Compression Ignition (HCCI) engine is possible to achieve high thermal efficiency and low emissions. 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), a simple HCCI combustion control system is suggested, and the control system is evaluated experimentally.

It has been investigated that the inhomogeneity of fuel concentration in the pre-mixture is effective as a method for controlling the combustion duration on HCCI combustion experiment. In this research， we analyze the effect of local inhomogeneity in a pre-mixture on HCCI combustion characteristic using chemiluminescence imaging and thermodynamic analysis with RCM and Optical engine. It is expected that， it will provide us with knowledge about control of ignition timing and combustion duration， and also how to avoid a knocking for achieving high IMEP.

Although HCCI engine attracts attention as a next-generation internal combustion engine, it must clear subjects, such as control of suitable auto-auto-ignition timing, and reservation of high IMEP avoiding knocking, for the utilization. Moreover, it is also an important factor to design the fuel that is ignited at the suitable crank angle. From the viewpoint of chemical reaction theory, it is necessary to investigate the fundamental combustion characteristic of the fuel in HCCI combustion. In this study, using two kinds of fuels, its attention was paid to the technique of controlling auto-ignition timing of HCCI combustion appropriately by changing the mixed rate of them, and fundamental investigation about the ignition and combustion characteristic was conducted. DME and n-Butane with low temperature reaction, and Hydrogen, which is easy to be ignited, are mixed to Methane without the reaction, respectively. The mixed rate of two kinds of fuel investigated the influence affect auto-ignition timing, and the influence affect IMEP by a combustion experiment and numerical computation with elementary reactions. When the rate of DME, n-Butane, and Hydrogen was made to increase from the result of a combustion experiment, it turns out that auto-ignition temperature became lower and auto-ignition timing became early. On the contrary, it became clear for it to be able to operate, while delaying auto-ignition timing to expansion stroke and securing high IMEP by making the rate of Methane increase. From the result of numerical calculation, it became clear that the promotion effect of DME, n-Butane, and Hydrogen shows up by accelerating oxidization of intermediate species, such as H2O2 and HCHO, and supplies of OH radical.

The purpose of this study is to propose an estimation method which can estimate NOx, PM, CO2 emission from vehicle to roadside. Driving tests were preformed on the road by a diesel freight vehicle with on-board measurement system, measuring actual emissions. Vehicle speed, acceleration, travel resistance were focused to clarify the influence on behavior of vehicle emission factors. Based on these results, vehicle emission factors model was composed and evaluated. As a consequence, it became possible that NOx, PM, CO2 emission factors are estimated with a high degree of accuracy.