Experimental and Modeling Studies on the Correlation Between Auto-Ignition Delays and the Methane Number of Liquefied Natural Gas (LNG) and Liquefied Biogas (LBG)

Bo Shu,Jiaxin Zheng,Sonal K Vallabhuni,Sumit Agarwal,Ravi X Fernandes

doi:10.3389/fmech.2020.00047

Abstract

Liquefied natural gas (LNG) and liquefied biogas (LBG) as transport fuel constitute one of the pillars of the European clean fuel strategy. LNG and LBG often contain higher hydrocarbons up to C5 that lead to more complex ignition properties when utilizing them in gas engines. Therefore, it is essential to understand their combustion behavior and to quantify the abnormal combustion such as knocking propensity with correlation to the methane number (MN). Currently, there is no traceable standard to define the MN and the literature algorithms give no consistent results for the same LNG/LBG mixtures. In this study, the correlation between MN and ignition delays of several LNG/LGB mixtures containing C1 to C5 alkanes and nitrogen were investigated at temperatures between 870 and 1550 K at 10, 20, and 40 bar and with equivalence ratios of 0.4 and 1.2. Good correlations have been observed for mixtures with MN 50 to 90 at high temperatures. At intermediate temperatures, discrepancies were found between mixtures with same MN but different C1 to C3 compositions. Moreover, addition of butane and propane isomers at low vol.% showed no effect on the IDTs at intermediate temperatures.

Highlights

To meet the goals of the Paris Agreement1, limiting the global warming to 2◦C above pre-industrial level, carbon dioxide (CO2) emissions from transportation and combustion-based power generation need to be reduced
In order to obtain a better understanding of the ignition property of the investigated Liquefied natural gas (LNG)/liquefied biogas (LBG) mixtures, sensitivity analyses were performed under the conditions of interest to provide deeper insights on the ignition behaviors
The ignition delay times (IDTs) of different LNG/LBG and reference mixtures were investigated in a high-pressure shock tube and a rapid compression machine covering temperatures from 870 to 1,550 K, pressures of 10, 20, and 40 bar, and equivalence ratios of 0.4 and 1.2

Summary

INTRODUCTION

To meet the goals of the Paris Agreement, limiting the global warming to 2◦C above pre-industrial level, carbon dioxide (CO2) emissions from transportation and combustion-based power generation need to be reduced. The use of LNG/LBG as fuel in engines can induce very different combustion behaviors, e.g., knock resistance, thermal efficiency, and emissions. The knocking behavior of LNG/LBG depends on the composition of the gas and on the design of the test engines and the operating conditions. As a measure for the knocking propensity, they used the Propane Knock Index (PKI) instead of methane/hydrogen references It is defined as the fraction of propane in a mixture of methane/propane which shows the same knock propensity as the investigated gas (Gersen et al, 2015).

H8 n-C4 H10 i-C4 H10 n-C5 H12 i-C5 H12

RESULTS AND DISCUSSIONS

Modeling Results

CONCLUSIONS