Fuel Structure Effects on Surrogate Alternative Jet Fuel Combustion

摘要

This study reports ignition delay measurements from combustion of four binary surrogate mixtures for alternate jet fuel: n-dodecane/n-heptane (47.5/52.5% by liquid vol.), n-dodecane/iso-octane (47.9/52.1% by liquid vol.), n-dodecane/methylcyclohexane (49.0/51.0% by liquid vol.) and n-dodecane/m-xylene (75.0/25.0% by liquid vol.). The experiments were carried out at the University of Dayton Research Institute (UDRI) heated shock tube facility, and covered a pre-ignition temperature range of 950-1500 K at a pre-ignition pressure of ～16 atm., an equivalence ratio of 3 and an argon concentration of 93% (by mol). Experimental data were modeled using the 2014 SERDP mechanism for jet fuel surrogates. Similar ignition delay times were measured among the tested surrogate blends, confirming previous observations regarding the controlling role of normal alkanes during the induction period. The experimental observation were also compared with modeling results and showed good agreements. A kinetic analysis of the SERDP 2014 mechanism was also performed highlighting the major chemical pathways relevant to the pre-ignition chemistry. In addition, a wide speciation of combustion products was also carried out under the test conditions. All the aliphatic blends reported similar emissions, whereas the presence of m-xylene produced lower emissions than the aliphatic surrogate blends at lower temperatures. For certain species (light gases) this experimental observation was also supported by the kinetic mechanism predictions. However, aromatic species formed from combustion of n-dodecane/m-xylene surrogate blend were always overestimated by the model and in poor agreement with experimental observations. The results also confirmed the role of acetylene in assisting growth of large PAHs and formation of soot.