Usually premixed flame propagation and laminar burning velocity are studied for mixtures at normal or elevated temperatures and pressures, under which the ignition delay time of the premixture is much larger than the flame resistance time. However, in spark-ignition engines and spark-assisted compression ignition engines, the end-gas in the front of premixed flame is at the state that autoignition might happen before the mixture is consumed by the premixed flame. In this study, laminar premixed flames propagating into an autoigniting dimethyl ether/air mixture are simulated considering detailed chemistry and transport. The emphasis is on the laminar burning velocity of autoigniting mixtures under engine-relevant conditions. Two types of premixed flames are considered: one is the premixed planar flame propagating into an autoigniting DME/air without confinement; and the other is premixed spherical flame propagating inside a closed chamber, for which four stages are identified. Due to the confinement, the unburned mixture is compressed to high temperature and pressure close to or under engine-relevant conditions. The laminar burning velocity is determined from the constant-volume propagating spherical flame method as well as PREMIX. The laminar burning velocities of autoigniting DME/air mixture at different temperatures, pressures, and autoignition progresses are obtained. It is shown that the first-stage and second-stage autoignition can significantly accelerate the flame propagation and thereby greatly increase the laminar burning velocity. When the first-stage autoignition occurs in the unburned mixture, the isentropic compression assumption does not hold and thereby the traditional method cannot be used to calculate the laminar burning velocity. A modified method without using the isentropic compression assumption is proposed. It is shown to work well for autoigniting mixtures. Besides, a power law correlation is obtained based on all the laminar burning velocity data. It works well for mixtures before autoignition while improvement is still needed for mixtures after autoignition.

通常在正常或升高的温度和压力下研究混合物的预混火焰传播和层流燃烧速度，在这种情况下，预混物的着火延迟时间远大于阻燃时间。然而，在火花点火发动机和火花辅助压缩点火发动机中，预混火焰前面的终端气体处于在混合物被预混火焰消耗之前可能发生自燃的状态。在这项研究中，考虑到详细的化学和运输过程，模拟了传播到自燃二甲醚/空气混合物中的层流预混火焰。重点是在与发动机相关的条件下，自燃混合物的层流燃烧速度。考虑了两种类型的预混火焰：一个是预混合的平面火焰在没有限制的情况下传播到自燃二甲醚/空气中；另一个是在密闭室内传播的预混球形火焰，为此确定了四个阶段。由于该限制，未燃烧的混合物被压缩至接近或在与发动机相关的条件下的高温和高压。层流燃烧速度由恒定体积的传播球形火焰方法以及PREMIX确定。获得了在不同温度，压力和自燃过程下自燃DME /空气混合物的层流燃烧速度。结果表明，第一阶段和第二阶段的自燃可以显着加速火焰的传播，从而大大提高层流燃烧速度。当第一阶段的自燃发生在未燃烧的混合物中时，等熵压缩假设不成立，因此传统方法不能用于计算层流燃烧速度。提出了一种不使用等熵压缩假设的改进方法。它显示了对自动点燃混合物的良好效果。此外，基于所有层流燃烧速度数据获得幂律相关性。它对自燃前的混合物效果很好，而对自燃后的混合物仍需要改进。