Strategies for Reduced Engine-out HC, CO, and NOx Emissions in Diesel-Natural Gas and POMDME-Natural Gas Dual-Fuel Engine
2022-01-0559
03/29/2022
- Event
- Content
- Dual-fuel engines employ precisely metered amounts of a high reactivity fuel (HRF) such as diesel at high injection pressures to burn a low reactivity fuel (LRF) such as natural gas, which is typically fumigated into the intake manifold. Dual fuel engines have demonstrated the ability to achieve extremely low engine-out oxides of nitrogen (NOx) emissions compared to conventional diesel combustion at the expense of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. At low engine loads, due to the low in-cylinder temperatures oxidation of HC and CO is challenging. This results in both compromised combustion and fuel conversion efficiencies. The experimental campaign discussed in this paper consisted of a set of six basic engine control parameters that were strategically varied to find the best possible efficiency-emissions trade-offs for both diesel- and poly-oxy methylene dimethyl ether (POMDME)-natural gas fuel combinations on the University of Alabama single-cylinder research engine (UASCRE) based on the PACCAR MX-11 heavy-duty engine platform. The control parameters investigated include: (1) Start of Injection of HRF (SOI1), (2) percentage energy substitution of LRF (PES), (3) introduction of the second injection (SOI2), (4) split ratio (i.e.) ratio of the duration of the first injection to the duration of the second injection, (5) rail pressure, and (6) intake boost pressure. At a fixed gross indicated mean effective pressure (IMEPg) of 5 bar (representative of typical low load operating point) and an engine speed of 1339 rpm (B speed of the SCRE), SOI1 was varied to determine the lowest engine-out NOx point. Using that SOI1 as reference and not-to-exceed (NTE) limits of: (1) Indicated specific NOx <1 g/kWh, (2) maximum pressure rise rate (MPRR) <10 bar/deg, and (3) coefficient of variation (COV) of IMEPg <10%, the rest of the five control parameters were systematically varied. Based on HC and CO vs NOx trade-offs, the best PES, SOI2, and split ratio were determined to achieve the lowest possible HC emissions. Subsequently, rail pressure sweeps showed minimal impact on performance and emissions between 500 bar and 1500 bar. Finally, reducing the intake boost pressure significantly reduced CO emissions to achieve the best operating point. Compared to the baseline diesel-natural gas case, HC and CO were reduced by ~88% and ~82%, respectively, in addition to ~21% improvement in the indicated fuel conversion efficiency. Whereas for POMDME-natural gas, HC and CO were reduced by ~85% and ~92%, respectively, in addition to ~20% improvement in the indicated fuel conversion efficiency. Furthermore, due to the high oxygen content of POMDME (47% m/m), engine-out soot emissions were reduced to zero measurable filter smoke number (FSN) for all conditions investigated.
- Citation
- Hariharan, D., Partridge, K., Narayanan, A., Anandaraman, N. et al., "Strategies for Reduced Engine-out HC, CO, and NOx Emissions in Diesel-Natural Gas and POMDME-Natural Gas Dual-Fuel Engine," SAE Technical Paper 2022-01-0559, 2022, .