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Guilherme Mazui

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What is the Difference Between RON and MON?

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The difference between RON and MON lies in the conditions under which they are measured and their purposes.

RON (Research Octane Number) is a measure of a fuel's performance at low temperatures and low speeds, simulating engine performance at 600 rpm and 120°F (49°C) air temperature. It is determined by comparing the performance of the fuel and different mixtures of iso-octane and n-heptane in a test engine with a variable compression ratio under controlled conditions. RON ratings are used by petroleum refiners, engineers, car manufacturers, and fuel marketers to determine the price and optimize fuel/engine pairings.

MON (Motor Octane Number) is a measure of fuel performance under more severe conditions, such as high temperatures and high speeds, simulating engine performance at 900 rpm and 300°F (149°C) air temperature. MON is calculated using a test engine with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. A modern pump gasoline's MON is usually about 8 to 12 points lower than its RON, but there is no direct link between the two values. Optimizing fuel and engine pairings is one of the key uses of MON.

In most countries, the octane number displayed on fuel pumps is the average of RON and MON, also known as the Anti-Knock Index (AKI) or (R+M)/2. This value is used to indicate the fuel's resistance to knocking or pinging during combustion, which can affect engine performance and efficiency.

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  • What is the Difference Between RON and MON?
  • Comparative Table: RON vs MON

    • Comparative Table: RON vs MON

    Research Octane Number (RON) and Motor Octane Number (MON) are two different measures of fuel performance. Here is a table highlighting the differences between RON and MON:

    Parameter RON MON
    Definition Indicates the combustibility of engine fuel at low speeds and temperatures. Denotes how a fuel behaves at full-throttle range, calculated at high speeds and temperatures.
    Engine Speed Typically 600 rpm. Typically 900 rpm.
    Conditions Low temperatures and low speeds. High temperatures and high speeds.
    Knocking Sensitivity Less prone to knocking. More prone to knocking.
    Fuel Sensitivity 8 to 12 octane number difference between RON and MON. Anti-Knock Index (AKI) is the average of RON and MON.

    RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, while MON is determined at a higher engine speed, challenging the fuel's anti-knocking tendency at higher compression ratios. The difference between RON and MON is known as the fuel's sensitivity.

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    Guilherme Mazui

    Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.