Numerical Investigation of Methane Number and Wobbe Index Effects in Lean-Burn Natural Gas Spark-Ignition Combustion

Abstract

A larger use of natural gas in internal combustion engines will reduce the dependence upon petroleum imports. However, large variations in gas composition as a result of the gas origin and/or gas treatments applied can affect engine performance and emissions. This study used a three-dimensional computational fluid dynamics internal combustion engine model (validated with experimental data) to investigate the effect of adding heavier hydrocarbons (ethane and propane) to the gas mix. The simulation investigated the effects of spark timing, intake pressure, equivalence ratio, and engine speed when the engine operated with six different natural gas blends (methane number from 50 to 100 and Wobbe index from 48 to 58) that had a nonlinear relationship between the methane number and the Wobbe index. The results showed that a lower methane number and a higher Wobbe index increased and advanced in-cylinder pressure, advanced the combustion phasing, decreased the ignition lag, and shortened the combustion duration, regardless of the operating condition as a result of the higher laminar flame speed and energy density. In addition, it increased nitrogen oxides emissions but lowered unburned hydrocarbon emissions. A higher sensitivity to gas composition was found when the methane number was lower than 70. Moreover, the results suggest that gas composition will not affect lean-burn operation if the methane number is above 70. This suggests that the engine control system of a diesel engine converted to lean-burn natural gas spark-ignition operation will adjust to changes in natural gas composition as long as the methane number of the gas is at least 70.

Impact of Liquefied Natural Gas Composition Changes on Methane Number as a Fuel Quality Requirement

“…(3) Boiling temperature range (Table 2); (4) Relative density (the ratio of the average molecular weight of gas to that of air), ( Commonly the most important quality criterion used by the LNG recipient is the so-called Wobbe index [25,26]. In many countries, the maximum limit of the Wobbe index of natural gas is assumed around 56-57 MJ/m n 3 .…”

“…Highly developed engines are designed for MN ≥ 80 so that they can achieve high power, low emissions and excellent fuel economy. Lower methane number values can reduce the economics of gas engine applications but increase greenhouse gas emissions or decrease engine efficiency [25,29]. Considering the above issues, changes in standardization which describes the acceptable limits of methane number for internal combustion engines should be expected in near future.…”

The Effects of Ultra-Low Viscosity Engine Oil on Mechanical Efficiency and Fuel Economy

“…Since most of the friction losses in the ICE occur at the cylinder inner surface with piston and piston ring mating and crankshaft bearing friction, the exploration of friction reduction for these sliding friction pairs is mainly in the areas of lubrication additives, application of advanced coating and surface technologies, precise lubrication theory and simulation techniques. Other works performed an overview of the combustion technologies that have been tested able to improve the CO 2 and the NOx-Soot trade-offs such as specific bowl design, innovative fuel injection systems [7][8][9][10] and clean combustion technologies [11,12]. Studies have shown that reducing oil viscosity can be effective in improving fuel efficiency, but the problem that accompanies the application of lower viscosity oils is the accentuation of wear problems caused by the inadequate lubrication carrying capacity of lower viscosity oils [13].…”

Multiobjective optimization of the cooling system of a marine diesel engine

“…Furthermore, the outer coolant temperature of the ICE has a considerable effect on hydrocarbon (HC) emissions. [29][30][31][32][33][34] The evaporation of fuels is affected by the in-cylinder temperature of the engine: a low in-cylinder temperature results in a poor homogenous mixture. Therefore, the fuel is traditionally enriched in the engine to produce a relatively richer mixture, which leads to the ignition of a small amount of vaporized fuel, thus significantly sacrificing fuel economy and increasing hydrocarbon (HC) and carbon monoxide (CO) emissions.…”