Effect of Mixture Condition on Combustion of Fuel〜Air Inhomogeneous Mixture in a Constant-Volume Vessel

近年来，直接喷射分层装药火花点火发动机已进入商用市场。这些发动机的热效率在轻型驾驶环境下大大提高。这些发动机的燃烧可能是由于火焰在燃料浓度梯度下从富燃料或化学计量燃料向贫燃料混合物的传播，但其确切机理尚未揭示。对这种繁殖的研究还很少。因此，本研究的目的是从根本上研究无湍流燃烧。血管直径25mm，长度200mm。丙烷在一段时间内从容器的下部供应。之后丙烷燃料逐渐向上扩散，形成燃料浓度梯度。首先，采用激光诱导荧光法（LIF）在不燃烧的情况下，确定了沿容器方向燃料浓度场的变化。其次，用容器底部的火花点燃混合物，并通过高速纹影照片观察火焰的发展。根据容器内的压力历史，分析了燃烧的起始阶段和主要阶段以及最大压力。讨论了火花塞附近燃料浓度和容器内燃料浓度场的影响。在均质混合物中，火焰有转变为容器中间的郁金香火焰的趋势。然而，在分层浓度场中，由于在容器末端前存在稀薄混合物，这种趋势变弱，火焰在发展的过程中熄灭。通过改变波长，用单色仪测定了火焰中CH、OH和C2的自由基种类。在不久的将来，将需要对火焰的熄灭进行详细的观察，并讨论火焰与路易斯数或扩散系数之间的关系。

Recently direct injection stratified charge spark-ignition engines have appeared in the commercial market. The thermal efficiency of these engines increased enormously around light duty of the driving. The combustion in these engines is probably due to the flame propagation under concentration gradient of the fuel from rich or stoichiometric to lean mixture, however, precise mechanism has not been revealed yet. Research of such propagation has been hardly done. Therefore, the purpose of this study is to investigate the combustion without turbulence fundamentally. The vessel of 25mm in diameter and 200mm in length was used. Propane was supplied from near the lower side of the vessel during a certain period. After that, the fuel of propane diffuses gradually to the upward direction and forms gradient of fuel concentration. At first, the change of the fuel concentration field along the vessel was confirmed with laser induced fluorescence (LIF) without combustion. Second, the mixture was ignited by a spark at the bottom of the vessel and the flame development was observed by high-speed Schlieren photographs. The initial and main stages of the combustion and the maximum of the pressure were analyzed from the pressure history in the vessel. The effects of the fuel concentration near the spark plug and fuel concentration field in the vessel were discussed. In homogeneous mixtures, the flames have the tendency of changing to the tulip flame in the middle of the vessel. However, in stratified concentration field, the tendency becomes weaker and the flame quenches on the way of the development due to the existence of the lean mixture before the end of the vessel. And radical species of CH, OH and C2 from the flame were detected with a monochrometer by changing the wavelength. In the near future, the observation of the quenching of the flame will be needed in detail and the relation between the flame and the Lewis number or diffusion coefficient will be discussed.