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Utilizing the Ignition Quality Tester (IQT) to determine the impact of fuel physicochemical propert

Greg Bogin,Assistant Research Professor,Department of Chemical Engineering,Colorado School of Mines,Golden, COABSTRACT:The goal of increased combustion efficiency with reduced emissions has sparked increased interest in new technologies for advanced combustion engines such as Low Temperature Combustion (LTC). LTC involves the combustion of thoroughly premixed fuel and air, utilizing high compression ratios and lean equivalence ratios which produce relatively long ignition delay times (compared to typical diesel engines). LTC utilization produces two desirable characteristics: i) high engine efficiency due to high compression ratio and unthrottling, and ii) low NOx and PM emissions due to minimization of traditional high-temperature flame fronts and locally fuel-rich zones. LTC engines, however, present significant challenges as traditional engine control strategies (ignition coil control for Spark Ignition or start-of-injection timing for Compression Ignition) are not employed. Fuel mixture autoignition kinetics dictate ignition timing, resulting in significant control system decoupling. Attaining LTC using petroleum-based fuels (and eventually biofuels) is achievable through the optimal coupling of the fuel injection process with in-cylinder fluid mechanics, and an improved understanding of kinetic pathways to auto-ignition. This requires a concerted approach of experiments and numerical modeling to quantify the effects of fuel chemistry and physical properties on combustion timing, combustion efficiency, and emissions.
A comprehensive understanding of fuel effects on combustion efficiency and emissions is essential for predictive models used to design advanced combustion engines utilizing the LTC regime. It is also essential as non-petroleum based fuels, which can vary widely in fuel chemistry, are adopted. Accomplishing this task requires a research device capable of studying realistic fuels (e.g. low volatility) which are difficult to study using traditional research apparatus such as shock tubes and rapid compression machines. The Ignition Quality Tester (IQT™) is a constant volume, spray combustion device designed solely to measure ignition delay, from which a Derived Cetane Number (DCN) is calculated using ASTM method D6890-09. The experimental capabilities of the IQT have been expanded to allow investigation of fuel effects on combustion timing and emissions. In parallel, a computational fluid dynamics (CFD) model was developed using KIVA-3V and linked with CHEMKIN to provide the first significant insights into the coupling of fuel spray physics and chemical kinetics for the IQT. The coupling of experiments and modeling enables fundamental research on the physical and chemical fuel effects on combustion, with the benefit of maintaining the link to the ASTM method for DCN. The CFD model accurately and efficiently reproduces ignition behavior of n-heptane; predicting that the combustion event is governed by autoignition and that dispersed ignition events occur throughout the combustion chamber. 2-methyl-hexane (an isomer of n-heptane having similar physical properties) produces longer ignition delay (ID) times compared to n-heptane, in agreement with rapid compression machines studies. The longer ID of 2-methyl-hexane verifies that chemical kinetics dominate over the physical effects of the fuels. The longer ID also results in higher NOx emissions. Thus, the IQT can bridge the gap between fundamental fuel research and actual internal combustion engine research.

Location: Seaver Science Library (SSL) Rm 150

Audiences: Everyone Is Invited

Contact: April Mundy