Westport HPDI Natural Gas Engine Can Switch to Hydrogen Later

Westport's HPDI engine runs on compressed natural gas or renewable natural gas now and can accept hydrogen later, either blended with natural gas or as a 100% hydrogen fuel, without the 99.999% purity requirement that fuel-cell trucks demand.

Can the HPDI engine run on hydrogen without a dedicated clean fuel system?

Yes. The HPDI high-pressure direct-injection fuel system does not require hydrogen to meet the 99.999% purity standard that fuel cells need, according to Westport. That eliminates the need for a dedicated super-clean distribution network and avoids the cost of liquefying hydrogen and hauling it in cryogenic trailers.

The engine's fuel adaptability means fleets can spec natural-gas HPDI tractors today and introduce hydrogen as the fuel becomes available and affordable in their operating region. Hydrogen adoption can start as a blend with natural gas, then scale to 100% hydrogen as infrastructure and economics improve.

What fuels does the HPDI engine accept?

The HPDI platform runs on compressed natural gas, renewable natural gas, hydrogen, or a blend of natural gas and hydrogen. Westport positions the fuel flexibility as a hedge, truck makers can integrate HPDI for natural gas in the near term, then leverage the same engineering and manufacturing investment to extend the technology to hydrogen without a ground-up redesign.

Why does lower hydrogen purity matter for fleets?

Fuel-cell trucks require hydrogen at 99.999% purity, which drives up production cost and limits fueling-station compatibility. The HPDI combustion engine tolerates lower-purity hydrogen, which can be produced and distributed through less-expensive infrastructure. For a fleet running regional routes out of a single terminal, that could mean on-site hydrogen production from electrolysis or steam methane reforming without the capital expense of ultra-high-purity equipment.

Westport's claim is that fleets avoid the chicken-and-egg problem of hydrogen infrastructure, they can start with low-cost CNG or RNG, which already has 900-plus public fueling stations in the US, then add hydrogen as local supply comes online.

What's the adoption path Westport envisions?

Westport describes a three-stage rollout: fleets run CNG or RNG initially, introduce hydrogen as a blend when a local source becomes available, then transition to 100% hydrogen as fuel cost and availability justify the switch. The HPDI fuel system's on-engine hardware remains compatible across all three stages.

The pitch assumes that hydrogen will become "increasingly affordable" over time. Current wholesale hydrogen prices in California, the state with the most developed hydrogen infrastructure, range from $16 to $36 per kilogram at the pump, equivalent to $5.30 to $12 per diesel gallon on an energy basis. Compressed natural gas trades around $2.50 per diesel-gallon equivalent in the same market. Westport's model depends on that gap narrowing.

How does HPDI compare to fuel-cell trucks on the road today?

Fuel-cell Class 8 tractors from Hyundai, Nikola, and Daimler are in limited production, with total US deployment under 300 units as of early 2025. All require 99.999% hydrogen purity and cryogenic storage at minus 423°F. Fueling infrastructure for those trucks is concentrated in Southern California, with fewer than 60 heavy-duty hydrogen stations nationwide.

The HPDI engine is a compression-ignition internal-combustion platform, not a fuel cell. It uses a small diesel pilot injection to ignite the natural gas or hydrogen charge: typical pilot fuel consumption is 5% to 10% of total fuel energy. That means HPDI is not zero-emission even on 100% hydrogen; it still produces trace NOx and particulate from the diesel pilot. Fuel-cell trucks produce only water vapor at the tailpipe.

Westport has not disclosed horsepower, torque, or fuel-economy figures for the HPDI engine in the source material. The company has not announced OEM partnerships or production timelines for a high-horsepower HPDI variant suitable for Class 8 line-haul.

What's the maintenance and parts picture for dual-fuel engines?

Dual-fuel natural-gas engines add complexity versus diesel, high-pressure fuel rails, gas injectors, separate fuel filters, and pilot-diesel injection hardware. Cummins Westport ISX12N natural-gas engines, which use a spark-ignited design rather than HPDI, have shown oil-change intervals of 25,000 to 40,000 miles depending on duty cycle, shorter than the 50,000-mile intervals common on diesel ISX12s. HPDI's compression-ignition design may close that gap, but Westport has not published service-interval data.

Hydrogen combustion introduces additional unknowns. Hydrogen's low lubricity and high flame speed can accelerate valve-seat wear and increase the risk of pre-ignition. Fleets running early hydrogen-combustion prototypes from other manufacturers have reported more frequent valve adjustments and higher oil-consumption rates than diesel baselines. Whether HPDI's direct-injection strategy mitigates those issues is not yet documented in customer-fleet data.

What does this mean for a small fleet weighing alternative fuels?

The HPDI engine's value proposition is optionality: buy natural-gas capability now, keep the door open for hydrogen later. That matters if you operate in a region where RNG is cheap and hydrogen infrastructure is coming but not here yet.

The risk is that you pay for fuel-system flexibility you may never use. If hydrogen remains expensive or unavailable in your lanes, you've spec'd a more complex engine than a straight CNG or diesel platform. If hydrogen becomes the dominant fuel faster than Westport expects, you've locked in a combustion engine that still burns a diesel pilot instead of a zero-emission fuel cell.

For fleets with access to low-cost RNG and a long equipment-replacement cycle, HPDI offers a hedge. For fleets in regions with no near-term hydrogen plans, a simpler CNG engine or a diesel with renewable diesel capability may be the lower-risk spec. Westport's bet is that hydrogen infrastructure will arrive unevenly, and that fleets in early-adopter markets will pay a premium for fuel flexibility.