Design and Testing of a Dedicated Hydrogen-Fueled Engine

Hydrogen-fueled internal combustion engines

“…Thus, the piston top land clearance can be decreased to prevent hydrogen flames from propagating into the top land; Swain et al [180] use a clearance of 0.152 mm to quench the hydrogen flame. Some researchers have changed the crevice volumes and/or piston rings with the aim of reducing the reflow of unburned mixture from the second land (the crevice volume between the top two piston rings) to the top land [180,182,183] (preventing ''fueling'' of a top land flame during exhaust and intake).…”

“…This suggests that the small quenching distance of hydrogen (together with the wide flammability limits), allowing combustion in the piston top land (the crevice volume above the top piston ring), is a parameter that has been overlooked by many workers. Hydrogen engines have been demonstrated, running on stoichiometric mixtures without any occurrence of backfire, by careful selection of piston rings and crevice volumes, without any need for timed injection or cooled exhaust valves [180]. Workers that have paid attention to increased cooling, enhanced ''oil control'' by mounting different piston rings, increased scavenging etc., attribute the resulting wider backfire-free operation region to a reduction of hot spots but have simultaneously (sometimes possibly without realizing it) taken measures to suppress crevice combustion.…”

“…Some researchers have changed the crevice volumes and/or piston rings with the aim of reducing the reflow of unburned mixture from the second land (the crevice volume between the top two piston rings) to the top land [180,182,183] (preventing ''fueling'' of a top land flame during exhaust and intake). The smaller quenching distance of a hydrogen flame also implies an increased thermal load for the piston top land; Berger et al [184] report changes (a special coating) to the top piston ring groove area to account for this.…”

“…Measures include the use of cooled exhaust valves; multi-valve engine heads to further lower the exhaust valve temperature [171,173,179]; a proper oil control [147]; additional engine coolant passages around valves and other areas with high thermal loads [180] (if possible); the delay of fuel introduction to create a period of air cooling (using timed manifold or DI); and adequate scavenging (e.g., using variable valve timing [163,181]) to decrease residual gas temperatures. …”

Lean Hydrogen Combustion

“…Swain et al (1996) designed an intake manifold to take advantage of the characteristics of hydrogen. The important feature is the use of large passageways with low-pressure drop, which is possible with hydrogen fueling since high intake velocities required for fuel atomization at low engine speeds are not necessary (Swain et al, 1996). With the use of a large diameter manifold, Swain et al reported a 2.6% increase in peak power output compared to that for a small diameter manifold.…”