SJTU team proposes new dual-fuel combustion mode: intelligent charge compression ignition (ICCI); high efficiency, low NOx
A team at Shanghai Jiao Tong University (SJTU) is proposing a new combustion mode—intelligent charge compression ignition (ICCI)—for ultra-high efficiency and low emissions simultaneously. A paper on ICCI is published in the journal Fuel.
ICCI aims to realize flexible and controllable in-cylinder charge stratification fed by two complementary fuels: gasoline and diesel. To enable this dual-fuel combustion mode, the team utilized two common-rail direct-injection systems independently on a modified single-cylinder engine, each injection system being controlled by its own on-limits electronic control unit, respectively.
Li et al.
In general, a majority of gasoline fuel is injected early to create a premixed background charge, while the rest of the fuels are alternately injected at compression stroke to create controllable reactivity stratification. During the injection process, diesel and gasoline are multi-stratified and mixed with the piston stroking upward. Eventually, before the fuel ignition happening, the ideal stratification completed, which means that the concentration and reactivity in the cylinder were adjusted towards the optimal conditions. The injection timing, fuel split ratio and fuel split number can be changed with the engine operating condition variation, modulating the in-cylinder stratification in real-time. The ignition timing and combustion rate are controllable so that the high thermal efficiency and low NOx emissions could be obtained.—Li et al.
Experimental results showed that high indicated thermal efficiency close to 50% and low NOx emissions well below 0.12 g/kWh were simultaneously achieved at 85% gasoline ratio.
Based on the optimal gasoline ratio, multi-injection strategies of ICCI mode can further improve thermal efficiency and emissions, the team said.
They also compared ICCI with other combustion modes, including reactivity-controlled compression ignition (RCCI); G85 dual direct injection (DDI); G85; and G70 single direct injection (DI) strategies were carried out. In the similar operating conditions, ICCI combustion got better performance compared with other combustion modes, achieving about 2% increased indicated thermal efficiency in comparison to RCCI or DDI mode and near zero NOx emissions compared with DI combustion.
The relationship between ITE, combustion efficiency, CA50 and combustion duration with the variation of gasoline ratio. Li et al.
Slightly more specifically:
Compared with ICCI mode, single-fuel DI strategies fuel with G70 and G85 have the unacceptable cyclic variation and combustion noise more than 4% and 2 MW/m2, respectively, and still had relatively high NOx emissions within the range of 3–15 g/kWh. G85 DDI strategies obtained lower ITE less than 45% and higher CO and THC emissions more than 10 g/kWh compared with ICCI mode. ICCI mode also had better PM emissions than other single-fuel combustion mode.
ICCI mode and RCCI mode both obtained extremely low NOx emissions less than 0.6 g/kWh. ICCI broke through the limitations cause by PFI in dual-fuel combustion. Therefore, it has a higher ITE than RCCI along with lower CO emissions. However, RCCI had better PM emissions than ICCI in the present experiment.
During the fuel ratio adjustments of ICCI mode, it was found that with the gasoline ratio increasing, the combustion phasing was delayed, while NOx emissions decreased but CO and HC emissions increased. At 8 bar IMEP, the best optimal target in the experiments was the condition of 85% gasoline ratio with the highest efficiency of 49% and relatively low NOx emissions of 0.1 g/kWh simultaneously.
ICCI has a large potential based on the further optimization in the future, the team concluded.
Zilong Li, Guan Huang, Yaoyuan Zhang, Wenbin Zhao, Jing Li, Zhuoyao He, Yong Qian, Xingcai Lu (2020) “Dual fuel intelligent charge compression ignition (ICCI) combustion: Efficient and clean combustion technology for compression ignition engines,” Fuel, Volume 279, 118565 doi: 10.1016/j.fuel.2020.118565