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Biodiesel Emissions Analysis Program

There has been increasing interest in recent years in the use of biodiesel as a substitute for petroleum-based diesel fuel. Biodiesel is derived from plant or animal fat-based oils or their transesterified counterparts. Several studies have found HC and PM benefits from the use of biodiesel, and its lubricity characteristics and renewability are also motivators for its use. Several municipalities and States are considering mandating the use of low levels of biodiesel in diesel fuel.

Description of Analyses

Using existing data, the EPA's biodiesel emissions analysis program sought to quantify the air pollution emission effects of biodiesel for diesel engines that have not been specifically modified to operate on biodiesel. The program examined the emission impacts of biodiesel and biodiesel/diesel blends for both regulated and unregulated pollutants, as well as fuel economy. The program was not intended to include investigations of other aspects of biodiesel use, such as:

  • Engine durability
  • Renewability/full fuel lifecycle emissions
  • Materials compatibility
  • Biodiesel production feedstocks or costs
  • Fuel storage stability
  • Cold flow properties
  • Lubricity
  • Cost

The statistical analyses correlated emission impacts, in terms of percent change with respect to a baseline fuel, with the concentration of biodiesel in a biodiesel/diesel blend. These emission impacts could potentially be a function of any of the following variables:

  • Engine/vehicle technology
  • Base fuel to which biodiesel is added
  • Light versus heavy-duty
  • Highway versus nonroad
  • Test cycle
  • Type of biodiesel

The degree to which these variables were taken into account depended on the amount and type of available data.

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