超希薄予混合圧縮自着火機関試案

抄録

A novel concept is proposed to realize "Ultralean Premixed Compression-Ignition Operation". Compression ignition of lean mixtures has allowed us to overcome the lean limit of flame propagation. Operating mixture strength can be decreased to an equivalence ratio of less than 0.2. Premixed fuel and air, introduced into a cylinder and compressed by piston upstroke motion, will ignite very near the top dead center. A combination of two-component fuel, namely : a low-octane liquid fuel injected into a very homogeneous high octane gaseous fuel/ air mixture just before the intake valve, enabled us to control the self-ignition timing and pressure rise rate at the onset of hot ignition. For an operating condition of engine speed and load expected in practice an optimal combination of fuel amounts can be found, i. e. the optimal octane value of the total charge and the total amount of both fuels should be selected separately for the best performance. Pure propane and n-heptane are utilized to demonstrate the feasibility of this concept. Lower fuel consumption and lower CO and NO emissions are also accomplished compared to those of spark-ignition engines.