These benefits are not necessarily additive but hold the promise of a total NOX reduction of
over 50 percent from the current baseline of a two-valve DI diesel with no EGR and mechanically
controlled fuel injection system that typically has a NOX emission level of 0.8 g/mile.
The technologies also appear to have very favorable effects on consumer related variables. The
variable geometry turbocharger and four-valve head will lead to improved power and better
drivability, while pilot injection and EGR will result in reduced noise and vibration. Hence, the
tradeoffs of emission control are quite favorable for a diesel engine.
Some current DI diesels such as the Audi 2.5L engine already feature “pre-injection” and
electronic injection timing but still have NOX emissions of 0.8 g/mi.^65 Nevertheless, manufacturers
believed that DI diesels could achieve 0.4 g/mi NOX with all of the above technologies, though
they agreed it would be difficult to attain this goal. Hence, there is some potential for DI diesels to
meet all current “Tier I“ standards without a NOx waiver and without a NOx catalyst.
Manufacturers also believed that it was unlikely that LEV/ULEV standards of 0.2 g/mi NOx
could be met without a NOX reduction catalyst. Most automanufacturers alSO commented On the
fact that, although lean-NOx reduction catalysts have undergone major development in the last
few years, their application to diesel engines was far more difficult than their application to lean-
bum gasoline engines. Little data on lean-NOx catalysts with diesel engines was presented by the
manufacturers, but there is guarded optimism that such catalysts may emerge from the research
stage within the next five years. Commercialization may occur after 2005, making the diesel a
contender in cars even under LEV standards by the 2010 timeframe.ti
Light trucks are potentially a more attractive market for the diesel. Even now, diesels sell very
well in the 8,500 to 14,000 lb light-heavy truck market (classified as heavy-duty by EPA). The
higher torque of the turbocharged DI diesel is more attractive to pickup truck owners, and light-
truck emission standards are somewhat less stringent than passenger car standards. Moreover, the
fuel consumption advantage makes diesels more cost-effective in trucks because they consume
more fuel each year.
Direct Injection Diesel Price Effect.
Costs of the DI diesel in both naturally aspirated form and in turbocharged form were estimated
as a $100 increment over a IDI 4-cylinder engine. As the base IDI itself is a $400 to $450
increment over a gasoline engine, and turbocharging adds $450 to $500, the net RPE effect
should be about $950 to $1,050. The VW DI turbodiesel is priced at 1,600 DM ($1,085) above
the 1.6L gasoline engine, almost exactly at the upper limit of the above price estimate. Four-valve
DI diesels with lean-NOx catalysts will require another $110 (for the four-valves over two-valve)
and about $100 for the catalyst so the total price impact for four-cylinder turbocharged four-valve
65 D. Stock and R. Bauder, "The New Audi 5-cylinder Turbo Diesel Engine,” SAE paper 900648,1990-
66 There are a range of views concerning NOX catalysts for diesels. The Japanese, who are well advanced on lean-bum catalysts for gasoline
engines, are somewhat pessimistic about the potential for rapid progress on diesel catalysts; U.S.companies are more optimistic, and some believe
commercialization of such catalyst could come before the year 2000. One interesting reference point: diesel oxidation catalysts have recently been
introduced, 18 years after introduction of gasoline oxidation catalysts.