Severe Downsizing of a Three-Way Lean NOx Trap (3wLNT) Diesel Engine,
Inclusive Dates: 05/01/12 – 12/07/12
Background — Increased cost is driving the diesel engine out of the compact/small car market. SwRI's concept of a three-way lean NOx trap (3wLNT) diesel engine is a low-cost solution for light-duty diesel OEMs to meet emissions regulations without the need for exhaust gas recirculation (EGR) or an expensive selective catalytic reduction (SCR) system. The aftertreatment is essentially a three-way catalyst with a NOx adsorbing coating. The 3wLNT is a truly cost-effective solution.
Approach — The 3wLNT engine runs lean at light- to mid-load conditions and stoichiometric at mid to high loads. At lean light-load operation, the aftertreatment is used as a lean NOx trap. At high loads, the aftertreatment is used as a three-way catalyst by stoichiometric operation. While the concept is certainly cost-effective from a hardware point of view, there are technical challenges in the form of soot production and fuel economy. While it is accurate that stoichiometric engines without significant dilution from EGR have higher fuel consumption on a brake mean effective pressure (BMEP) to BMEP basis, the stoichiometric diesel concept lends itself to significant downsizing potential, which may overcome this deficiency. The down-sizing potential is greater than spark-ignited engines because a stoichiometric diesel engine does not suffer from engine-damaging knock or pre-ignition. The downsizing potential is greater than standard diesel also because there is no need for EGR and excess air. Therefore the 3wLNT concept engine is expected to have lower peak cylinder pressures allowing for higher BMEP levels to be achieved and less demanding turbo-charging requirements.
Accomplishments — Based on the accomplishments and results, the project is defined as a success. The major takeaways from this project are:
- A drivable vehicle that could meet complete light-duty drive cycles with combustion strategies radically different from a conventional diesel engine.
- Severe downsizing potential was proven possible with this kind of combustion strategy. As an example, the curb-side weight of a 2012 Ford F-150 is around 5,333 pounds. This 2.0 L Passat engine was able to drive a Ford F-150 sized vehicle on a chassis dyno over a U.S. Federal Drive Cycle without any limitations.
- Good transient performance as well as drivability was achieved for the heavier vehicle inertia tested on a chassis dyno.
- Fuel penalties between the combustion strategies => lean-burn and lean + stoichiometric combustion were within acceptable ranges.