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

最近，直喷式分层充气火花点火发动机出现在商业市场上。这些发动机的热效率在驾驶的轻量化附近有了极大的提高。这些发动机的燃烧可能是由于燃料浓度梯度下的火焰从富燃或当量混合到稀薄混合气的传播所致，但其确切的机理尚不清楚。对这种传播的研究还很少。因此，本研究的目的是从根本上研究无湍流燃烧。血管直径25 mm，长度200 mm。丙烷是在一定时间内从容器下侧附近供应的。之后，丙烷燃料逐渐向上扩散，形成燃料浓度梯度。首先，在不燃烧的情况下，用激光诱导荧光(LIF)技术证实了燃料浓度场沿容器的变化。其次，用容器底部的火花点燃混合物，并用高速纹影照片观察火焰的发展。从容器内的压力历程分析了燃烧的初始阶段和主要阶段以及压力的最大值。讨论了火花塞附近的燃料浓度和容器内燃料浓度场的影响。在均匀混合物中，火焰在容器中间有向郁金香火焰转变的趋势。然而，在分层浓度场中，由于容器末端前稀薄混合物的存在，发展过程中火焰熄灭的趋势变弱。通过改变波长，用单色仪检测火焰中的自由基物种CH、OH和C2。在不久的将来，将需要对火焰熄灭的详细观察，并将讨论火焰与刘易斯数或扩散系数的关系。

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.