Propane Vehicle Emissions
Propane fuel has a lower carbon content than conventional gasoline and diesel fuel. When used as a vehicle fuel, propane can offer life cycle greenhouse gas (GHG) emissions benefits over conventional fuels, depending on vehicle type, age, and drive cycle.
Increasingly stringent emissions regulations have led to the development of improved emissions control systems in conventional light-, medium-, and heavy-duty vehicles. These systems effectively control the levels of air pollutants emitted from the vehicle as a result of the combustion of gasoline or diesel fuel. Tailpipe emissions from propane vehicles are comparable to those of gasoline and diesel vehicles with modern emissions controls, and many modern propane engines meet the optional, more stringent low NOx standard.
Propane is frequently used to replace gasoline in smaller off-road applications, such as forklifts and commercial lawn equipment, and it provides benefits similar to those achieved in on-road vehicles.
Life Cycle Emissions
Life cycle analysis is a technique used to assess the environmental impacts of all stages of a product's life, including raw material extraction, processing, manufacturing, distribution, use, and disposal or recycling. When comparing fuels, a life cycle analysis may focus on particular portions of a fuel's life cycle, such as extraction-to-use or well-to-wheels, to determine the merits or problems associated with each fuel.
Argonne National Laboratory's Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model estimates the life cycle petroleum use and GHG emissions for multiple fuels. When this model is used to evaluate vehicles running on propane, it indicates that propane use reduces GHG emissions by nearly 13%, and when derived as a byproduct of natural gas production, propane reduces petroleum use by 99%. The Gas Technology Institute compared GHG emissions from forklifts, buses, and light- and medium-duty vehicles operating on various fuels in GHG and Criteria Pollutant Emissions Analysis.
Converting conventional vehicles is a viable option for incorporating propane into light-, medium-, and heavy-duty fleet operations. EPA also requires conversion system manufacturers to demonstrate that converted vehicles or engines meet the same emissions standards as the original vehicle or engine. It is also critical to follow all applicable codes and standards when performing a conversion. Therefore, it's important that conversions be completed by vetted and reputable qualified system retrofitters (QSR). Prior to agreeing to a vehicle conversion by a QSR, fleet managers should research the company and talk with other clients to ensure the conversions satisfied their expectations. Other best practices can be found in the report What Fleets Need to Know About Alternative Fuel Vehicle Conversions, Retrofits, and Repowers.