“Freedom from the soot/NOx tradeoff: Opportunities for MCCI of small-molecule fuels”
2022-01-0647
03/29/2022
- Event
- Content
- Air quality considerations continue to require increasingly strict limits on tailpipe emissions from heavy-duty vehicles across all sectors. In addition to more effective aftertreatment systems, lowering levels of engine-out NOx, soot, and other pollutants remains a priority. For diesel fuel, the traditional soot-NOx tradeoff is well known, as are the the soot- and NOx-forming regions on a plot of local temperature vs local equivalence ratio. These regions make managing simultaneous reduction of soot and NOx during mixing-controlled combustion of diesel fuel challenging However, the soot- and NOx-producing regions in a local temperature vs. local equivalence ratio plot are fuel-dependent. The soot-producing region is especially fuel-dependent, with fuels like methanol, ethanol, DME, and E85 producing very low amounts of soot even under the range of equivalence ratios present during mixing-controlled combustion. This change in contours of the soot-NOx tradeoff regions creates additional opportunity for engine tuning and optimization for low engine-out emissions. More specifically, the freedom from soot formation provides an additional degree of freedom for lowering engine-out NOx in pursuit of meeting future regulation such as the proposed 0.02g/hph level. This paper presents emissions results from a Cummins 15L heavy-duty engine converted to operate on 100% fuel-grade ethanol in a mixing-controlled combustion mode. Ignition of a low-cetane fuel and a mixing-controlled burn is accomplished through elevated pre-injection temperatures and fuel injection within 5 degrees of TDC. The emissions data show that for ethanol, engine-out emissions of soot are well below the threshold of 0.1g/hph, and as a result of the low soot formation, there is opportunity to calibrate the engine for low engine-out NOx without encountering a soot constraint. To demonstrate this, the engine was operated at a fixed power output, while the engine-out NOx were lowered from 2g/hph to 0.1g/hph using EGR and adjusted injection timing. Thermal efficiency remained nearly constant. Further, exhaust temperature remained constant throughout, providing opportunity for maintained aftertreatment conversion at lower engine-out emissions.
- Citation
- Blumreiter, J., "“Freedom from the soot/NOx tradeoff: Opportunities for MCCI of small-molecule fuels”," SAE Technical Paper 2022-01-0647, 2022, .