During the past decade, the automotive industry has converted more than 50 percent of its internal combustion engines from a traditional technology called port fuel injection (PFI) to a new technology called gasoline direct injection (GDI). The fundamental difference between the two engine types is that GDI engines inject fuel directly into the combustion chamber instead of the injection port of the PFI engine. Benefits of GDI technology—improved fuel economy, lower carbon dioxide (CO2) emissions, and increased power output—have resulted in rapid adoption. By 2025, the U.S. Environmental Protection Agency (EPA) projects that 93 percent of all vehicles produced will use GDI engines. However, the downside of direct fuel injection, according to a recent report in the journal Environmental Science & Technology, is a high level of black carbon (BC) aerosol emissions, which adversely affects both climate and public health. See also: Aerosol; Automobile; Carbon black; Fuel injection; Gasoline; Internal combustion engine
As strong absorbers of solar radiation, BC aerosols (commonly known as soot) are associated with climate warming. According to NASA, aerosols are not distributed evenly around the Earth, as greenhouse gases are. As a result, aerosol effects are felt more strongly on a regional scale. Because vehicle emissions are more concentrated in and around cities, regional warming effects of BC aerosols would dwarf any climate benefit that GDI engines generate from CO2 reduction. BC aerosols are also a source of fine particulate matter (PM2.5)—an air pollutant 2.5 micrometers or less in diameter. PM2.5 is an environmental risk factor for cardiovascular and pulmonary diseases as well as cancer. See also: Air pollution; Global climate change; Global warming; Greenhouse effect; Particulates; Public health; Solar radiation
It is not entirely clear how BC aerosol emissions originally evaded automotive engine designers. The most likely scenario is that engineers never tested for particulates because no particulate emission standard exists for gasoline engines. Because PFI engines produce a more complete combustion, resulting in almost no particulate emissions, the EPA applied particulate standards only to diesel engines. As there is no safe level of human PM2.5 exposure, automakers are investigating a number of potential solutions. Among the proposed solutions, short of switching to electric vehicles, are installing particulate filters, optimizing GDI engines’ injection system to produce less BC aerosols, and modifying fuel mixtures by using more ethanol in gasoline because the additional oxygen content would inhibit soot formation. See also: Alternative fuels for vehicles; Effects of electric-vehicle adoption on air quality; Ethyl alcohol; Risk assessment and management
