Experimental and numerical investigation of the Advanced Fuel Ignition Delay Analyzer (AFIDA) constant-volume combustion chamber as a research platform for fuel chemical kinetic mechanism validation

Abstract

Advanced combustion engine strategies that can offer increased efficiency and reduced emissions are enabled by numerical engine combustion simulations, requiring accurate chemical kinetic mechanism input. The Advanced Fuel Ignition Delay Analyzer (AFIDA) device can perform high quality, repeatable measurements of ignition delay (ID) times using small fuel quantities with high throughput. The AFIDA experiments involve liquid fuel injection into the heated and pressurized constant-volume chamber, producing an autoignition delay resulting from a combination of physical mixing and chemical kinetic processes, a complexity which makes the development of complementary numerical models necessary for the development and validation of chemical kinetic mechanisms. Modeling the device based on a homogenous approximation with reduced primary reference fuel (PRF) mechanism shows up to 75% error in the modeled vs. observed autoignition delay data for n-heptane and iso-octane at 10 bar (ɸ = 1.2–0.8) and 20 bar (ɸ = 0.6–0.4) over 973–648 K, whereas the use of a computational fluid dynamics (CFD) model reduces the discrepancy to within 25%. The homogenous approximation error is greatest for conditions where the observed ignition delay is short and the system is not sufficiently mixed (<30 ms), providing guidance to select a homogenous reactor vs. CFD modeling approach based upon desired accuracy. Experimental 20 bar iso-octane ID results show a larger magnitude of negative temperature coefficient chemistry compared to numerical results, indicating possible deficiencies in the PRF chemical kinetic mechanism. This characterization demonstrates the AFIDA as a capable research platform for chemical kinetic model development and validation.