Laminar Burning Velocities of Dimethyl Ether, n-Heptane and iso-Octane at High Pressure

Oxygenates, such as methanol or ethanol, are frequently used as blending components in standard gasoline. One oxygenate, dimethyl ether (DME), is also used as a fuel component in some regions of the world, for example in Asia. In addition, patent reviews show the potential of DME as a blending component in liquefied petroleum gas (LPG) or mixed with propane. The laminar burning velocity is one key parameter for the numerical simulation of gasoline engine combustion processes. Therefore, it is of great interest for modern engine development to understand the effect of oxygenates on the laminar burning velocity.

The experimental results have been conducted under engine-like conditions with elevated initial pressures of up to 20 bar and initial temperatures of 373 K. Experiments were done at equivalence ratios between 0.8 and 1.3. The experimental setup consists of a spherical closed pressurized combustion vessel with optical access. The filling procedure and filling setup have been significantly improved compared to previous work done in the same apparatus. Schlieren measurements coupled with a high-speed camera are used for image acquisition to track the expanding flame front. A post processing tool is used to extrapolate the measurements to zero stretch. Tested fuel components were DME, n-heptane and iso-octane. N-heptane and iso-octane results are new data with minimised standard deviations achieved by an optimised filling procedure and therefore presented in this study. Additionally, the experimental results obtained are compared to numerical simulations. High-temperature chemical kinetic models have been used for calculating laminar burning velocities of the considered fuel components. Finally, the experimental and numerical results are discussed in detail in conjunction with references found in literature.