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Characterization and system level study of air addition in a pilot ignited direct injection natural gas engine

University of British Columbia

The emissions from heavy duty engines must be reduced in light of their climate and health effects. Pilot-ignited direct injection natural gas engines (PIDING) allows cleaner combustion by using natural gas as the primary fuel instead of diesel. To achieve further emission reductions, the concept of air addition to natural gas, at various global equivalence ratio (Φ) and EGR rates was investigated in a heavy-duty mode of a PIDING engine. However, this concept requires compressed air over 300 bar, which may impose net compression work to the engine. Therefore, the system level implications were investigated by developing and characterizing a prototype compression system, and subsequently considering its compression work with the engine indicated efficiency. The investigations were carried out using a single cylinder research engine and an industrial reciprocating compressor. Fuel dilution by air addition was demonstrated to effectively reduce emissions of PM, CO, and THC. Particulate matter (PM) reduced exponentially, resulting in more than an order of magnitude reduction. Similarly, carbon monoxide (CO) was also reduced albeit with lower magnitude. The total unburnt hydrocarbons (THC) reductions with air addition were significant only at high EGR (> 12.5%). However, air addition significantly increased NOx emissions (up to factor of 2.5); but increasing the EGR rates by 6.5%-point may compensate for this. The net compression work was dependent on the engine operating conditions, number of compressor stages, and performance of the chosen compressor. Air addition resulted in indicated efficiency improvements on the order of 2.5%, which at high Φ were sufficient to compensate for the compression work of a three-stage reciprocating compressor. The same may be possible with even smaller and efficient 2-stage compressors. An optimization study suggests that air addition would be most effective at high values of Φ, EGR rates, and air addition. As an in-cylinder strategy, it has the potential to be used in conjunction with ultra-high EGR, to significantly reduce both PM and NOx emissions, while avoiding the typical issues of ultra-high EGR: combustion instabilities and high THC and CO emissions.

Text

2019-01-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/68303

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/