We propose a new method to apply hybrid fuel combustion to diesel engines in order to reduce NOx and smoke emissions. In hybrid combustion, subsidiary fuel is fed into intake air, whereas the main fuel of light-oil is directly injected into the combustion chamber as in conventional diesel engines. In this study, we tried to use two different kinds of fuels, di-methyl ether (DME) and gasoline as subsidiary fuels. DME, with a high cetane number and excellence in auto -ignition, is used only to afford preliminary combustion in the early compression period, which promotes and advances the ignition of the sprayed main light-oil and accordingly reduces emissions. Gasoline, by contrast, with no self-ignition characteristic in diesel engines, is used as a part of the main fuel to fill the engine cylinder with a uniform mixture before the injection of diesel fuel, the other main fuel, to ignite both the main fuels smoothly and lower emissions. Experiments with DME demonstrated successful ignition earlier than the conventional method and decrease of NOx from 160 to 120 ppm without smoke increase at 2 NL/min DME flow. Use of gasoline as the complementary main fuel eliminated smoke emissions and reduced NOx from 2700 to 1600 ppm.
副燃料を用いるハイブリッド燃焼に新手法を考案・適用し，ディーゼルエンジンからの有害排気物質の低減を図る。 従来通りのシリンダ内へ直噴する軽油主燃料の他に，副燃料を吸気空気に予混合して用いるが，狙う浄化機構の違いにより２つの性質の異なる副燃料を試みる。 一つは自着火性の高いディメチルエーテル（DME）で，少量を予混合して圧縮行程早期にシリンダ内で燃焼させ，後に噴射される主燃料軽油の燃焼をスムーズにし，排ガス浄化を図る方法。 もう一つは自着火しにくいガソリンで吸気を予混合化させ，主燃料噴射軽油量をその発熱相当分を減じ，噴霧軽油の気化均一に要する時間を短縮して浄化を図る方法。 先のDMEによる方法ではNOXが，後のガソリンによる方法では，スモークの低減にも効果が見られた。
hybrid combustion, diesel engines, subsidiary fuel, di-methyl ether (dme), gasoline, emission reduction