S
SkyPup
Guest
FUEL BASICS
To understand diesel fuel quality and how it impacts fuel mileage, you need to look at these key fuel properties:
• API Gravity — a scale used to measure fuel weight. The weight of a fixed volume of fuel is compared to the same volume of water. The lower the API, the heavier the fuel and the harder it is to burn. The higher the API, the lighter the fuel and the poorer the fuel mileage. Can be measured with a special fuel hydrometer. A good API number (measured at 60°F) would be 34 to 36. Kerosene, by comparison, has an API of 40 to 44.
• BTU Content — a measure of the fuel’s energy content. One Btu (British Thermal Unit) will generate enough heat to raise the temperature of one pound of water by 1°F. The higher the Btu content, the better your fuel mileage. A good fuel will have a Btu content of over 130,000 per gallon.
• Cetane — the fuel’s ignition quality or startability. It’s typically expressed as the fuel’s cetane index or rating. This is a calculation or estimation based on specific gravity, not an exact measure. To get the exact cetane number, the fuel needs to run in an engine for some time. The higher the cetane number, the better the engine will start in cold weather. A cetane of 40 is considered minimum, but 49 is ideal.
• Cloud Point — the temperature at which wax crystals begin forming in the fuel. The crystallization causes the fuel to cloud or haze. The fuel will still flow, but the wax could clog filters and fuel lines. Your fuel’s cloud point should be at least 10°F below the lowest temperature you expect on a trip. Although the actual cloud point cannot be changed with chemicals, you can use additives to reduce the size of thecrystals so that the fuel flows better.
• Pour Point — around 5° above the temperature at which the fuel solidifies or gels. Once fuel has gelled, it will not move at all. The pour point is usually lower than the cloud point and is easier to modify. Ideally, fuel should have a pour point 20° to 25° below the lowest temperature expected on a trip.
[This message has been edited by SkyPup (edited February 03, 2000).]
To understand diesel fuel quality and how it impacts fuel mileage, you need to look at these key fuel properties:
• API Gravity — a scale used to measure fuel weight. The weight of a fixed volume of fuel is compared to the same volume of water. The lower the API, the heavier the fuel and the harder it is to burn. The higher the API, the lighter the fuel and the poorer the fuel mileage. Can be measured with a special fuel hydrometer. A good API number (measured at 60°F) would be 34 to 36. Kerosene, by comparison, has an API of 40 to 44.
• BTU Content — a measure of the fuel’s energy content. One Btu (British Thermal Unit) will generate enough heat to raise the temperature of one pound of water by 1°F. The higher the Btu content, the better your fuel mileage. A good fuel will have a Btu content of over 130,000 per gallon.
• Cetane — the fuel’s ignition quality or startability. It’s typically expressed as the fuel’s cetane index or rating. This is a calculation or estimation based on specific gravity, not an exact measure. To get the exact cetane number, the fuel needs to run in an engine for some time. The higher the cetane number, the better the engine will start in cold weather. A cetane of 40 is considered minimum, but 49 is ideal.
• Cloud Point — the temperature at which wax crystals begin forming in the fuel. The crystallization causes the fuel to cloud or haze. The fuel will still flow, but the wax could clog filters and fuel lines. Your fuel’s cloud point should be at least 10°F below the lowest temperature you expect on a trip. Although the actual cloud point cannot be changed with chemicals, you can use additives to reduce the size of thecrystals so that the fuel flows better.
• Pour Point — around 5° above the temperature at which the fuel solidifies or gels. Once fuel has gelled, it will not move at all. The pour point is usually lower than the cloud point and is easier to modify. Ideally, fuel should have a pour point 20° to 25° below the lowest temperature expected on a trip.
[This message has been edited by SkyPup (edited February 03, 2000).]
