Phd defense: Experimental and numerical studies of the ignition of ammonia/additive mixtures and dimethyl ether burning velocities | L. (Liming) Dai

The incentive to limit global temperature rising and reduce man-made greenhouse emissions is driving the development and introduction of alternative fuels in current combustion engines. Ammonia and dimethyl ether (DME) both are considered as promising alternative fuels owing to their physical and chemical properties. This thesis focused on measuring the ignition delay times of ammonia and ammonia mixed with hydrogen, methane and DME, respectively, using rapid compression machine (RCM) and measuring the flame temperatures and burning velocities of DME/air mixtures using Raman scattering setup. The measurements were used to test the ability of chemical mechanisms describing the oxidation of these fuels. This study shows that all these additives show strong ignition-enhancing effect on NH3, while the effect of additives is non-linear. DME has the strongest ignition-enhancing effect on NH3, for instance, 5% DME addition decreases the ignition delay times of ammonia by 250K. During the course of this study a new NH3/DME mechanism that includes interactions between ammonia and DME species was developed, which predicts the ignition delay times of NH3/H2 and NH3/CH4 mixtures very well at the conditions studied. Kinetic analysis revealed that the ignition promoting effect of DME could be caused by its low temperature chain branching reactions. The measurements of DME/air flames were compared to predictions from one-dimensional flame calculations to assess the accuracy of different chemical mechanisms for DME oxidation. In some cases, the results permitted improved recommendations for the burning velocity of these mixtures.

Dissertation: http://hdl.handle.net/(...)66-908d-174d411f6fb6