C1/H2 Fuels at Elevated Pressures

Corporate Sponsor: ExxonMobil

The increased availability of natural gas at relatively low costs has generated interest in new applications for the fuel. Natural gas turbines are supplanting coal boilers as the primary means of generating electricity in the USA. Another interesting application is the use of natural gas in internal combustion engines, which have already hit the market for some commercial transportation applications [1].

There have been a number of computational predictive studies of the combustion of natural gas, primarily focused on its principle component, methane. For example, the Gas Research Institute’s effort in the 1990’s led to the widely used GRI combustion mechanism [2]. This mechanism, as well as subsequent improved mechanisms for the same application, perform well for near-atmospheric pressures over a range of equivalence ratios – as might be expected since they were parameterized using the available experimental data at those conditions. However, the mechanisms are less well tested and tend to show weaker predictive capabilities at the higher pressures relevant to internal combustion engines as well as gas turbine applications.

Here we aim to use our group’s expertise in chemical kinetic modeling to generate a mechanism that can be trusted for the combustion of methane in internal combustion engines. Next, we will extend the model to higher carbon number components of natural gas as well as potential fuel additives such as hydrogen or syngas.

Our initial work will use Extinction Strain Rate (ESR) as the principle value of interest for mechanism validation. Previous studies have focused on the use of parameters such as laminar flame speed and ignition delay for validation, but we believe ESR is a more challenging, and discriminating, feature. Motivating our use of ESR is recent work from the Ghoniem lab at MIT which has shown ESR to correlate strongly with turbulent flame structure and stability, which is important for predicting engine misfire [3]. This is a known issue for natural gas engines due to the relatively low combustion speed and ESR of methane, especially under lean and/or dilute conditions.

[1] CumminsWestport: http://www.cumminswestport.com/

[2] Frenklach et al. : http://combustion.berkeley.edu/gri-mech/

[3] Shanbhogue et al. : http://www.sciencedirect.com/science/article/pii/S001021801500382X