Propane Vehicle Emissions
Propane is a cleaner-burning fuel than conventional gasoline and diesel due to its lower carbon content. When used in vehicles, propane offers life cycle greenhouse (GHG) emissions benefits over conventional fuels, depending on vehicle type, drive cycle, and engine calibration. In addition, using propane in place of petroleum-based fuels may reduce some tailpipe emissions.
Increasingly stringent emissions regulations have led to the development of improved emissions control systems in conventional light- 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. Consequently, emissions from propane vehicles are comparable to those of gasoline and diesel vehicles with modern emissions controls.
Propane is frequently used to replace gasoline in smaller applications, such as forklifts and commercial lawn equipment. Because propane is a low-carbon, clean-burning fuel, a switch to propane in these applications can result in substantial reductions of hydrocarbon, carbon monoxide, oxides of nitrogen, and greenhouse gas emissions. In addition, propane is nontoxic, so it isn't harmful to soil or water.
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 GREET model estimates the life cycle petroleum use and greenhouse gas (GHG) emissions for multiple fuels. When this model is used to evaluate vehicles running on propane it found that propane use reduced GHG emissions by nearly 10%, and when derived as a by-product of natural gas production, propane reduced petroleum use by 98% to 99%, The Propane Education and Research Council compared GHG emissions from forklifts, buses, and light-duty trucks operating on various fuels in Propane Reduces Greenhouse Gas Emissions: A Comparative Analysis.
Converting conventional vehicles is a viable option for incorporating propane into light- and heavy-duty fleet operations. EPA requires conversion system manufacturers to demonstrate that converted vehicles or engines meet or exceed the same emissions standards as the original vehicle or engine. Therefore, it's important that conversions be performed by careful and reputable qualified system retrofitters, because converted vehicles could produce higher emissions levels than manufactured propane vehicles if conversions are not properly installed and calibrated.