Advanced Automotive Technology: Visions of a Super-Efficient Family Car

The latest designs of diesel engines recently unveiled in Europe are far superior to previous designs. Oxidation

catalysts and better fuel control have substantially improved particulate emission performance. Four-valve per

cylinder design and direct injection^2 have separately led to better fuel economy, higher output per unit weight, and

lower emissions—though NOX emissions are still too high. Compared with a current gasoline engine, the four-

valve indirect injection design will yield about a 25 percent mpg gain (about 12 percent gain on a fuel

energy basis), while the direct injection (Dl) design may yield as much as a 40 percent gain (30 percent fuel

energy gain).^3

The new diesels are likely to meet California’s LEV standards for HC, CO, and particulate, but will continue to

require a NOX waiver to comply with emission requirements. Although the four-valve design and other innovations

(e.g., improved exhaust gas recirculation and improved fuel injection) will improve emissions performance and may

allow compliance with federal Tier 1 standards, LEV standards cannot be met without a NOX reduction catalyst.

Although manufacturers are optimistic about such catalysts for gasoline engines, they consider a diesel catalyst to

be a much more difficult challenge.^4

2 Most light-duty diesels are of indirect injection design. Air and fuel is injected into a prechamber where combustion starts, with further

combustion taking place in the main combustion chamber. Although this design yields lower noise and NOx emissions, it is less efficient than directly

injecting the air and fuel into the combustion chamber.3 The difference between the miles per gallon and fuel energy gains are due to diesel having an 11 to 12 percent greater energy content per gallon

than gasoline. Some automakers are skeptical of the projected fueleconomy improvement of the DI diesel because of its remaining emissions
problems.4 As a reference point, oxidation catalysts for diesels were
commercially introduced in 1993, 18 years after their introduction for gasoline-fueled
vehicles.