H2-Engine Operation with EGR Achieving High Power and High Efficiency Emission-Free Combustion

Experimental investigation of hydrogen combustion in a single cylinder PFI engine

“…It is interesting to observe that a calibration featuring mediumhigh levels of EGR, high RAFR (high boost) and advanced combustion phasing (MFB50 ;8CA deg ATDC) represents, as reported in the literature, the best combination of parameters. 7,17 This optimized calibration setting provides also a quite good combustion stability, as measured through the CoV-IMEP: the green area is close to the leading edge of lower CoV-IMEP (\ 3%), and this happens thanks to the completeness of the hydrogen flame propagation process, notwithstanding a certain cycle-to-cycle variation in the pressure diagrams as apparent from Figure 9 for the same engine operating point 2000 rpm-6 bar BMEP. The high degree of combustion completeness (in excess of 99%, as measured through unburned hydrogen) has been recognized as a peculiar behavior of optimized lean hydrogen combustion (RAFR ;2.0O2.5), which exhibits fast flame propagation (up to 6 times faster than gasoline or CNG stoichiometric mixtures), higher tolerance to in-cylinder inhomogeneities (which allow to burn effectively locally richer/leaner pockets) and a minimal quenching distance.…”

“…In this case, as represented in the top left diagram, it is interesting to observe that there is a clear relationship between the attainable performance level and the corresponding engine-out NOx emissions, in other words ultra-low emissions H 2 -PFI ICEs need somewhat to compromise their power output. 7…”

“…In fact, the effect of EGR -which for H 2 -ICEs is essentially composed by recirculated, air-diluted water vapor -on hydrogen combustion and its relative benefit versus an equivalent fresh air dilution in controlling knock and NOx production is still a debated topic, not entirely comprehended and accepted in literature. 7 Figure 14 reports the results of two sweep variations of MFB50 (left) and EGR rate (right) on IS-NOx versus RAFR on 2000 rpm-6 bar BMEP engine operating point, as indicated by the legends. As the X-and Y-scales are the same for both figures, it is possible to capture the relative magnitude of both parameters: the effect of MFB50 appears to be slightly larger than the EGR one for a similarly practical variation in the controlling parameter (SA timing or EGR rate) and seems to hint that EGR rate is not as effective for H 2 combustion as it is for Diesel one.…”

“…However, as pros do exceed cons, this is the region targeted by the new combustion concepts described in Refs., 4–9 which will be examined in this paper and assessed via testing on a single-cylinder engine (SCE) purposely built. The SCE object of the present paper, in particular, features a homogenous port-fuel injection (PFI) combustion system and dedicated piston bowl profile for a retrofitted Diesel operating as spark-ignited H 2 monofuel that has been designed by PUNCH following extensive simulation activities described in Golisano et al 10 and Millo et al 11 which – in turn – leveraged CFD best-practices reported in the literature for hydrogen and gaseous fuel engines as Gerke and Boulouchos 12 and Esposito et al 13…”

Effect of modified combustion chamber configuration and enhanced squish flow on improving thermal efficiency in jet-plume-controlled direct-injection near-zero emission hydrogen engines

“…13–19 In recent years, numerical analysis of hydrogen combustion and research and development work aimed at applying hydrogen to large vehicles such as trucks and buses have been actively carried out. 20–23 Similar technologies are also being developed for fuel cells, which are another application of hydrogen fuel. 24–26 However, there are still many issues to be resolved in order to build a hydrogen-based society, including technical aspects and implementation of the necessary supply infrastructure.…”