General Motors has been a leading supporter of the renewable fuels industry, and is an advocate for the responsible and appropriate use of renewable fuels in the GM model vehicles that are designed for their use.
BIODIESEL: AN OVERVIEW
Biodiesel is a renewable diesel fuel that is manufactured from vegetable oils, recycled cooking greases or animal fats. Biodiesel can be made using a variety of feedstocks. Soybean oil, rapeseed oil (canola), palm oil, waste cooking oil and sunflower oil are among the most common sources for commercial biodiesel production. The biodiesel manufacturing process converts oils and fats into chemicals called long chain mono alkyl esters. These chemicals are also referred to as fatty acid methyl esters or FAME. In the manufacturing process, oils or fats are reacted with an alcohol (usually methanol) in the presence of a catalyst (usually sodium or potassium hydroxide) to form biodiesel and glycerin. Glycerin is an alcohol, and is a co-product of the process. It is removed from the final biodiesel product.
Raw vegetable oil, refined vegetable oil or recycled greases that have not been processed into biodiesel are not biodiesel and should never be introduced into the fuel system.
When it's well made and the quality is carefully controlled, biodiesel can be used as a blending component with ULSD (ultra low sulfur diesel) in controlled percentages, without adverse consequences.
General Motors endorses the use of biodiesel blends of 5% (B5) or less, and provides warranty coverage for Duramax diesel equipped vehicles operated on this fuel. The exception to this is vehicles ordered with SEO option 5F4, which allows use of biodiesel blends of up to 20% biodiesel (B20). (Check with VISS for specific VIN option content). Repairs to conditions caused by the use of fuels other than those the vehicle was designed to accept are not covered under the terms of the New Vehicle Warranty.
RISKS ASSOCIATED WITH BIODIESEL USE
Biodiesel has some unique characteristics that must be managed in order for it to be used as a reliable fuel. Management of those characteristics is one reason that OEM manufacturers limit the allowable percentage of biodiesel in diesel fuel.
Fuel instability is a significant concern for ULSD blends containing more than 5% biodiesel. Oxidation stability can lead to deposits fouling fuel filters and sticking injectors. Some concerns that have been encountered in tests with unstable B20 with Duramax diesel fuel systems included plugged jet pump nozzles and hardened and cracked or broken polymer tubing in the MRAs.
The less stable nature of the fuel can lead to deterioration from long periods of in-tank storage, as in the case of low use vehicles. This is similar to storing a lawn mower for the winter with gasoline in the tank. By the next season, the gasoline has varnished and clogs up the fuel system. Biodiesel oxidizes notably faster that 100% diesel fuel and the timeframe at which this could cause a problem is shorter than with regular diesel fuel.
Biodiesel is also less stable than regular diesel fuel when the vehicle is operated or stored at high ambient temperatures.
Additional concerns that need to be managed when using higher concentrations of biodiesel include:
- Biodiesel has poor cold temperature properties that can lead to a clogged filter and hard starting at low temperatures.
- The polar nature of biodiesel can disable water-fuel separators and allow water to pass through. Biodiesel also contains more water than No. 2 diesel fuel.
- The heating value for B100 is about 10% lower compared with No. 2 diesel, so B20 users experience a 1-2% loss in fuel economy.
- DPF effectiveness can be compromised from both oil contamination and reduced effectiveness resulting from high metal levels (residual catalyst) present in some processed biodiesel.
For these reasons, repairs to conditions caused by biodiesel usage in percentages that exceed the allowable design limits are not covered under the terms of the New Vehicle Warranty.
One challenge that dealers face in diagnosing fuel related conditions that may be caused by excessive concentrations of biodiesel is that there is currently no simple in-dealership test that can determine the percentage of biodiesel present in the fuel.
General Motors is working with SPX to develop a dealer tool that will allow the technician to quickly determine -- within minutes in the dealership -- the percentage of biodiesel present in a vehicle fuel sample.
- Thanks to Jay Dankovich
BIODIESEL: AN OVERVIEW
Biodiesel is a renewable diesel fuel that is manufactured from vegetable oils, recycled cooking greases or animal fats. Biodiesel can be made using a variety of feedstocks. Soybean oil, rapeseed oil (canola), palm oil, waste cooking oil and sunflower oil are among the most common sources for commercial biodiesel production. The biodiesel manufacturing process converts oils and fats into chemicals called long chain mono alkyl esters. These chemicals are also referred to as fatty acid methyl esters or FAME. In the manufacturing process, oils or fats are reacted with an alcohol (usually methanol) in the presence of a catalyst (usually sodium or potassium hydroxide) to form biodiesel and glycerin. Glycerin is an alcohol, and is a co-product of the process. It is removed from the final biodiesel product.
Raw vegetable oil, refined vegetable oil or recycled greases that have not been processed into biodiesel are not biodiesel and should never be introduced into the fuel system.
When it's well made and the quality is carefully controlled, biodiesel can be used as a blending component with ULSD (ultra low sulfur diesel) in controlled percentages, without adverse consequences.
General Motors endorses the use of biodiesel blends of 5% (B5) or less, and provides warranty coverage for Duramax diesel equipped vehicles operated on this fuel. The exception to this is vehicles ordered with SEO option 5F4, which allows use of biodiesel blends of up to 20% biodiesel (B20). (Check with VISS for specific VIN option content). Repairs to conditions caused by the use of fuels other than those the vehicle was designed to accept are not covered under the terms of the New Vehicle Warranty.
RISKS ASSOCIATED WITH BIODIESEL USE
Biodiesel has some unique characteristics that must be managed in order for it to be used as a reliable fuel. Management of those characteristics is one reason that OEM manufacturers limit the allowable percentage of biodiesel in diesel fuel.
Fuel instability is a significant concern for ULSD blends containing more than 5% biodiesel. Oxidation stability can lead to deposits fouling fuel filters and sticking injectors. Some concerns that have been encountered in tests with unstable B20 with Duramax diesel fuel systems included plugged jet pump nozzles and hardened and cracked or broken polymer tubing in the MRAs.
The less stable nature of the fuel can lead to deterioration from long periods of in-tank storage, as in the case of low use vehicles. This is similar to storing a lawn mower for the winter with gasoline in the tank. By the next season, the gasoline has varnished and clogs up the fuel system. Biodiesel oxidizes notably faster that 100% diesel fuel and the timeframe at which this could cause a problem is shorter than with regular diesel fuel.
Biodiesel is also less stable than regular diesel fuel when the vehicle is operated or stored at high ambient temperatures.
Additional concerns that need to be managed when using higher concentrations of biodiesel include:
- Biodiesel has poor cold temperature properties that can lead to a clogged filter and hard starting at low temperatures.
- The polar nature of biodiesel can disable water-fuel separators and allow water to pass through. Biodiesel also contains more water than No. 2 diesel fuel.
- The heating value for B100 is about 10% lower compared with No. 2 diesel, so B20 users experience a 1-2% loss in fuel economy.
- DPF effectiveness can be compromised from both oil contamination and reduced effectiveness resulting from high metal levels (residual catalyst) present in some processed biodiesel.
For these reasons, repairs to conditions caused by biodiesel usage in percentages that exceed the allowable design limits are not covered under the terms of the New Vehicle Warranty.
One challenge that dealers face in diagnosing fuel related conditions that may be caused by excessive concentrations of biodiesel is that there is currently no simple in-dealership test that can determine the percentage of biodiesel present in the fuel.
General Motors is working with SPX to develop a dealer tool that will allow the technician to quickly determine -- within minutes in the dealership -- the percentage of biodiesel present in a vehicle fuel sample.
- Thanks to Jay Dankovich
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