| CPC F02P 5/1502 (2013.01) [F02D 19/02 (2013.01); F02D 41/0025 (2013.01); F02D 41/0027 (2013.01); F02D 41/042 (2013.01); F02D 41/062 (2013.01); F02D 41/22 (2013.01); F02M 21/02 (2013.01); G01N 33/2835 (2013.01)] | 3 Claims |

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1. A fuel property determination apparatus that determines a component of liquefied natural gas stored in a tank as a fuel for an engine, the fuel property determination apparatus comprising a processor configured to:
when the engine is being driven, calculate an ignition retard control amount for avoiding knocking in the engine and estimate a first methane number of the liquefied natural gas based on an index value indicating the ignition retard control amount;
when the engine is restarted from a stopped state, estimate a second methane number of the liquefied natural gas based on the first methane number, a remaining amount of the liquefied natural gas when the engine stops, and a stop time of the engine; and
when the first methane number or the second methane number is less than a threshold, notify that a property change has occurred in the liquefied natural gas.
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