Hydrogen Fueled Engines

Hannu Jääskeläinen

This is a preview of the paper, limited to some initial content. Full access requires DieselNet subscription.
Please log in to view the complete version of this paper.

• Hydrogen as Engine Fuel
• Abnormal Combustion
• Hydrogen Fumigation

Hydrogen as Engine Fuel

Hydrogen as a fuel for internal combustion engines offers very low emissions of PM, THC and CO. While tailpipe CO₂ emissions from the fuel are zero, the overall life cycle CO₂ emissions will of course depend on how the hydrogen is produced. The primary pollutant that needs to be considered is emissions of NOx which, on an engine-out basis, will be comparable to that from many hydrocarbon fuels. PN emissions may also be a concern. Key technologies that require further development to make hydrogen engines suitable for vehicle applications include high density on-board storage, several key engine technologies and suitable aftertreatment systems.

High density hydrogen storage remains a significant challenge. Gaseous storage is still the primary option that is commercially available but in the longer term, cryogenic or chemical storage could offer higher storage density and lower storage costs.

Key engine technologies that require development include boosting systems, mixture preparation, avoiding pre-ignition and suitable materials. Two-stage boosting systems that efficiently provide the high air flow and EGR requirements are essential to ensuring competitive BMEPs and low engine-out NOx emissions. Direct injection of hydrogen after IVC would help limit boost requirements while providing high power density and avoiding the risk of backfire [5603].

Hydrogen embrittlement of typical ICE materials requires new design approaches and alternative materials. While most engine components represent a low risk to embrittlement, currently used combustion chamber and crankcase materials could represent an elevated risk and require further assessment [5602].

Emissions of NOx are the primary emissions of concern related to hydrogen engines and suitable aftertreatment systems will be required. Urea SCR is a ready technology that could be employed but because of the increased condensation risk, washcoat technology and packaging mats may need to be adapted. H₂-SCR is another option and could avoid the need for urea but requires further development. Of the emissions arising from the combustion of lubricating oil, PN may be of most concern and could require exhaust filtration [5603]. If urea SCR is used, urea generated particles could also be generated and may require filtration. In one example for a direct injection test engine, a 170% increase in PN emissions relative to gasoline was noted that was attributed to enhanced lubricant involvement in the combustion process as a result of hydrogen’s low quenching distance, jet-wall impingement and lubricant vapor entrainment into the gaseous jet [5601]. Ammonia emissions could also be possible under conditions that generate rich combustion.

Another hydrogen engine challenge is the accumulation of hydrogen in the crankcase that, because of the wide flammability range of hydrogen, can present an explosion hazard. Venting the crankcase with additional fresh air to ensure the crankcase mixture remains below the flammability limit is one option. Dilution air flow of 8 to 10 times the blow-by volume drawn into the crankcase with a vacuum pump is one option that has been tested. Oil separators had to be resized and the piston ring pack optimized with higher tension rings, smaller end gaps and modified grooves to ensure blow-by rates did not become excessive with the lower crankcase pressures [5602].

Examples of modern hydrogen engine developments include:

• Work by IAV on a port-injected heavy-duty 13 L hydrogen engine that could meet future ultra-low NOx emissions. The concept applies VVA to achieve low load de-throttling and high load Miller cycle, a 10:1 compression ratio to achieve an estimated peak BTE of 41% [5476].
• A low-pressure direct-injection (LPDI) fuel system has been developed by Liebherr that operates at injection pressures of 30 to 60 bar and can be used as part of a common rail system in a spark-ignited engine or part of a dual-fuel system [5605].
• Yuchai demonstrated hydrogen combustion in a YCK16H engine using direct in-cylinder injection with high-pressure common rail that can realize homogeneous combustion or stratified combustion as required [5606].
• Westport’s adaptation of its HPDI fuel system for hydrogen [5799].
• Cummins’ adaptation of its B, L and X-Series engine portfolios to operate on hydrogen.

In addition to conventional piston engines, other power plant types can be fueled with hydrogen including rotary engines, gas turbines and the argon power cycle.

###