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.