Koji Kitano

Effects of GTL Fuel Properties on DI Diesel Combustion

Reduction of vehicle exhaust emissions is an important contributor to improved air quality. At the same time demand is growing for new transportation fuels that can enhance security and diversity of energy supply. Gas to Liquids (GTL) Fuel has generated much interest from governments and automotive manufacturers. It is a liquid fuel derived from natural gas, and its properties - sulphur free, low polyaromatics and high cetane number - make it desirable for future clean light-duty diesel engines. In this paper, the effects of distillation characteristics and cetane number of experimental GTL test fuels on direct injection (Dl) diesel combustion and exhaust emissions were investigated, together with their spray behaviour and mixing characteristics. The test results show that the lower distillation test fuels produce the largest reductions in smoke and PM emissions even at high cetane numbers. This is linked to the enhanced air/fuel mixing of the lighter fuel in a shorter time. The high ignitability and short ignition delay resulting from the high cetane number of all the GTL samples proved effective for reduction of unburnt emissions and combustion noise. Some experimental results are also presented when a modern high speed Dl diesel passenger car is run on neat GTL fuel and conventional diesel fuel. As the test results show, some benefits of GTL have been confirmed in exhaust emissions.

Research of the DI Diesel Spray Characteristics at High Temperature and High Pressure Ambient

乗用車用の小型ディーゼルエンジンにおいて比出 力・静粛性・排気性能等の向上が要求され,これらの 要求に対し,燃料噴射装置にはコモンレール噴射シス テムが採用されている.ディーゼルエンジンでは,そ の噴霧の質がエンジン性能(比出力・静粛性・排気性 能等)に大きく影響するため,エンジン・噴射系開発 において,エンジン筒内または同等環境場での噴霧挙 動の詳細解析(蒸気濃度分布解析,混合気形成過程の 解析など)が求められている.近年それだけでなく, 開発期間の短縮化から,噴霧の定量的な解析によるエ ンジン・噴射系への開発指針,方向性の提案が望まれ ている.ディーゼル噴霧の混合気形成過程の解析とし ては,LIEF(Laser Induced Exciplex Fluorescence) 法を用いた蒸気濃度の定量化があるが,蛍光強度の圧 力・温度依存性や,蛍光剤の熱分解,レーザの減衰等 が精度のよい計測を困難にしている. そこで本研究では,小型ディーゼルエンジンにおけ る混合気形成過程の解明及び,これを考慮したエンジ ン・噴射系への開発指針・方向性提案を目指し,蛍光 強度の圧力・温度依存性を考慮した蒸気濃度の準定量 化手法を構築した.また,定容燃焼容器を用い, エン ジン筒内と同等の環境場での,ディーゼル噴霧の混合 気形成過程について考察を行なった. 2.蒸気濃度検定 2)