研究発表

The dynamics model and model-based controller (LQG servo controller) have been constructed to improve performance of diesel engine at transient condition. The input parameters of the dynamics model are injected fuel quantity, injection timing, external EGR ratio and boost pressure. In the model, one cycle is discretized into 7 representative points such as EVC, IVC, fuel injection, ignition, maximum pressure, EVO and IVO. The precision of the prediction of the model and the responsiveness of the controller were checked.

TRecent researchers point out that the fuel and the oil are mixed on the cylinder liner and then released from it. During the compression stroke the released droplets reach the auto ignition temperature before flame induced by spark ignition propagate to the spots of droplets, and it is called Pre-ignition. When pre-ignition is occurred, sometimes severe pressure happens and damages the engine severely. This work investigates effects of gas inhomogeneity induced by droplets of fuels and oils on the auto ignition timing and temperature in the direct-injection spark ignition (DISI) engine by means of detailed numerical calculation using multi zone model of CHEMKIN-PRO by changing initial temperature and initial equivalence ratio. In order to assume inhomogeneity in the combustion chamber, 16 zones by multiplying 4 types of equivalence ratio and 4 patterns of temperature is used for detailed numerical calculation. In this study used n-heptane that has to low-temperature oxidation (LTO). Consequently, we found that initial in-cylinder gas pressure affects the auto-ignition of air-fuel mixture and there is possibility to lead to cause Pre-ignition.

In Dimethyl Ether(DME) indirect production processes, DME have a reforming process to separate Methanol. DME has a high cetane number and Methanol has a high octane number. Each fuel has a different combustion characteristics and reactivity. So, this paper was investigated on the combustion characteristics of DME and Methanol. Basically, Methanol has an effect of retarding ignition. However, Within 10% of total carbon mole number in DME, Methanol slightly changed the onset timing of Low Temperature Reaction (LTR) with increasing thermal-ignition preparation range. It means that controlling combustion phasing of DME can be possible without eliminated LTR. In case of IMEP(Indicated Mean Effective Pressure), the highest IMEP was shown within 10% of total carbon mole number in DME

This study investigates the EGR effect under the condition of boost pressure on homogeneous charge compression ignition(HCCI) combustion engine using numerical methods. The calculation is carried out using a single-zone model included in CHEMIKN-PRO. The detailed chemical-kinetic mechanisms and thermodynamic parameters for n-heptane, iso-octane and PRF(Primary Reference Fuel) from Lawrence Livermore National Laboratory(LLNL) are used for this study. The results show that the EGR affects the heat release, the amount of heat release decrease. Hence IMEP decrease with EGR ratio increase. The EGR addition under the condition of boost pressure enhanced the autoignition reactivity, the amount of heat release increased. As a result, we confirm that combined EGR and boost pressure incrase the IMEP maintaining the proper PRR.

燃焼室の急峻な熱発生により発生する圧力波を逆位相となるタイミングでの第二の熱発生により相殺し，燃焼騒音を低減させる手法がある．圧縮自己着火過程において燃料を追加することにより，二段のピークを持つ熱発生過程を実現する方法およびそのタイミングを検証した．

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 of degree of constant volume, thus thermal efficiency could be improved.

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.

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 of degree of constant volume, thus thermal efficiency could be improved.

米国におけるシェールガスおよび天然ガス自動車の動向について解説した