Westport Fuel Systems & AVL conclude high-efficiency H2 powertrain can outperform fuel cells in TCO for heavy-duty applications
A model-based analysis by Westport Fuel Systems and AVL indicates that H2-HPDI (High Pressure Direct Injection with pilot ignition)—a combustion approach for hydrogen in engines—has the potential to achieve fuel economy close to that of a fuel-cell electric vehicle (FCEV) for heavy duty applications, due to its high efficiency at both part and full loads.
In a joint publication, WFS and AVL conclude that the combined high efficiency and lower system costs relative to FCEVs make H2-HPDI the most capital efficient means to use hydrogen and lower CO2 emissions near-term and that it has the potential to remain competitive with fully industrialized FCEV in the future.
In the paper, “Total Cost of Ownership (TCO) Analysis for Heavy Duty Hydrogen Fueled Powertrains”, the authors investigated three potential combustion approaches for hydrogen:
H2-PFI SI (Port Fuel Injection with Spark Ignition)
H2-ECDI SI (Early Cycle Direct Injection with Spark Ignition)
H2-HPDI (High Pressure Direct Injection with pilot ignition)
The researchers find that H2-HPDI significantly outperforms the other combustion approaches in thermal efficiency. Hydrogen operation with the current WFS HPDI fuel system outperforms natural gas in terms of thermal efficiency, mainly due to lower equivalence ratio for H2 at given fueling energy level, higher kinetic energy for H2 jets as well as higher tolerance of H2 combustion to fuel rich operation.
Comparison of engine indicated efficiency with three different combustion approaches (PFI SI, ECDI SI and HPDI) for H2 with a diesel reference under full load operation. Source: Westport/AVL
Hydrogen combustion engines significantly reduce CO2, HC and PM emissions, leaving NOx as the most prominent tail pipe emission. For H2-HPDI under identical operating conditions compared to a diesel engine it is expected that the NOx emissions would be higher due to higher temperature combustion of H2.
The models indicate NOx emissions can be managed with EGR and commercially available Urea-SCR NOx exhaust aftertreatment technology. H2 is a strong reducing agent and its potential use for exhaust aftertreatment could certainly be explored.
The H2-HPDI engine, as modeled, eliminates more than 98% of CO2 emissions. There is a small quantity of CO2 contributed by the combustion of the pilot fuel and the trace amounts contributed by the engine lubricating oil and by the SCR NOx reagent (AdBlue).
The paper then undertakes a comprehensive TCO analysis, applying inputs from Westport Fuel Systems HPDI hydrogen (H2-HPDI) simulations and HPDI 2.0 operating costs with AVL’s existing TCO models for diesel and fuel cell powertrains.
Our analysis shows that a high efficiency hydrogen ICE powertrain (namely H2-HPDI) can outperform fuel cell electric vehicles in terms of TCO. This is possible because H2-HPDI leverages powertrain systems in high volume production today, while achieving near fuel cell-like efficiency in heavy duty applications. Fleets will appreciate a product that meets the same performance characteristics of today’s conventional diesel trucks without the product development risk and costs associated with fuel cells. HPDI 2.0 is already used by large fleets today, reducing CO2 by 23% with fossil LNG, and delivering net zero carbon emissions when used with bioLNG.—David Johnson, CEO of Westport Fuel Systems