Improved Spark Ignition Engine Efficiency through Lean Turbocharged Operation

A production turbocharged V-6 engine of 3.8 liter (231 cu. in.) displacement volume was used in this study of lean turbocharged operation. The engine was modified for lean operation (A/F = 19–20:1) and manual control of the fuel flow, compressor discharge pressure, and EGR rates. Test conditions included loads and speeds to simulate road-load and 4% grade operating conditions, as well as constant intake manifold pressure tests.

The results from the test program indicated that lean turbocharged operation has a potential for increased efficiency and reduced NOx emissions if operated at brake mean effective pressures of 500 kPa and above. For these operating conditions, HC and CO emissions are comparable to those of the naturally aspirated engine. NOx emissions were reduced by up to 50% over those for the naturally aspirated engine with EGR. Efficiency increases of up to 3 points (10%) were observed. Satisfactory detonation control for engines operating at these conditions will require comprehensive control of equivalence ratio, spark timing, and compressor discharge pressure.