Technical Reports

Investigation of an Anti-Knock Index and Hydrocarbon Emissions of Various Natural Gas Blends

  • 13
  • Apr
  • 2016
AUTHOR: Federal Railroad Administration
OFFICE: RPD
SUBOFFICE: RPD-32
REPORT NUMBER: DOT/RPD/ORD-16/07
KEYWORDS: Locomotive, Natural Gas, Diesel, Dual Fuel, Engine, Knock, Combustion, Methane Number, MWM Methane Number
ABSTRACT: The North American rail industry is examining the use of natural gas to reduce fuel costs for locomotives that are powered by dual fuel engines. This report evaluates the ability of an existing methane number algorithm to predict rapid combustion in a dual fuel engine. The Methane Number index, which quantifies the propensity of a gaseous fuel to autoignite, has the ability to well-characterize engine knock in spark-ignited combustion. However, the ability of the methane number, which was originally developed for spark-ignited engines, to predict a fuel’s “knock” behavior in dual fuel combustion is not fully understood. Specialized natural gas fuel blends are tested in a dual fuel engine and induced to rapid combustion. For fuels that should exhibit similar knock behavior, the transitions to rapid combustion occurred at significantly different conditions. This demonstrated that the existing methane number algorithm, while excellent for spark-ignited engines, did not fully predict the propensity for rapid combustion to occur in a dual fuel engine within the scope of this study. In its current form, a methane number algorithm can be used to conservatively rate dual fuel engines. It is possible that a new reactivity index for dual fuel combustion might allow ratings to be less conservative.

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