2012 IR&D Annual Report

Severe Downsizing of a Three-Way Lean NOx Trap (3wLNT) Diesel Engine,

Principal Investigators
Ryan Roecker
Sankar Rengarajan

Inclusive Dates:  05/01/12 – Current

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 SCR system. The after-treatment is essentially a three-way catalyst with a NOx adsorbing coating. The 3wLNT is a truly cost-effective solution.

Photo: Testing FTP 75 cycle on chassis dyno with lean-stoichiometric switching.
 Testing FTP 75 cycle on chassis dyno with lean-stoichiometric switching.

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 after-treatment is used as a lean NOx trap. At high loads, the after-treatment 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 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 — This project is on-going and currently in Phase II. The accomplishments to date are as follows:

  1. Set up a valuable platform that is complete in terms of hardware and software.
  2. Operated a diesel engine at stoichiometric conditions and quantified fuel penalty compared to lean burn operation at steady state.
  3. Explored downsizing potential at engine loads and speeds for a typical light-duty drive cycle (NEDC).
  4. Tested the vehicle on the chassis dyno with increased inertia simulating a downsized engine.
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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.