The natural gas is injected at the end of the compression stroke. Under the pressures found in the combustion chamber of a normal diesel engine, natural gas requires a higher ignition temperature than diesel. To assist with ignition, a small amount of diesel fuel is injected into the engine cylinder followed by the main natural gas fuel injection. The diesel acts as a pilot, rapidly igniting the hot combustion products, and thus the natural gas.

The two fuels are not pre-mixed with the intake air before they enter the combustion chamber so there is no risk of engine knock and therefore no need to lower the compression ratio and peak torque output. The compression ratio of an engine with Westport HPDI is the same as the diesel engine on which it is based, which results in fewer changes to engine components and preservation of the fuel economy benefits associated with high compression.

As compared to diesel fuel, directly injected natural gas burns with a lower adiabatic flame temperature and has a low propensity to the formation of carbon particles and therefore offers inherent nitrous oxide (NO_x) and particulate matter (PM) emissions benefits that provide more product engineering flexibility to allow powertrain designers to increase potential performance and customer value.

Westport HPDI 2.0 delivers performance and fuel economy equivalent to that of current high performance diesel-fueled engines, but with diesel substitution of more than 90%. This combination of high performance and high efficiency is critical for heavy-duty engines in demanding commercial applications, Westport notes.

Engines incorporating Westport HPDI 2.0 technology are engineered to be as similar to diesel-fueled versions as possible, minimizing capital investment and operational changes in the field.

In SI gasoline and natural gas engines, air and fuel are pre-mixed before entering the combustion chamber. Knock can occur when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.

Most current natural gas engines used in mobile applications require up to 30% reduction in compression ratio and 15% to 20% reduction in peak torque output to avoid the risk of engine-damaging knock, which reduces fuel economy and performance. Late-cycle direct injection of fuel—a principle fundamental to the Westport HPDI architecture—eliminates the danger of engine knocking.

Further, current SI engines use a throttle to meter the air to control the air/fuel mixture resulting in more constricted air flow into the engine and reduced fuel efficiency. Typical Diesel cycle engines—including engines with Westport HPDI—do not use a throttle to control the air-fuel ratio, as the gas directly injected into the combustion chamber at the end of the compression stroke can burn over a wide range of air fuel ratios.

HPDI 2.0 also continues the evolution of Westport natural gas storage and delivery systems with a new generation of proprietary fuel tank, fuel pump, and system controls that can match the vehicle range, performance, and driveability of diesel whether the vehicle is a long-haul truck, a locomotive, or a ship.

Exclusive Westport HPDI 2.0 systems features include:

• Optimization of combustion and higher efficiency: Provides improved fuel economy, which results in faster payback compared with Westport’s first-generation HPDI product and compared to spark-ignited natural gas engines. Westport HPDI engine efficiency under highway operations is approximately 44% compared with spark ignited natural gas engines at approximately 37%. This results in approximately 15% to 20% fuel economy improvement compared to spark ignited natural gas engines under typical operating conditions.

• Proprietary HPDI 2.0 dual common rail fuel injector: Designed for adaptability and multiple OEM engines ranging from 10 liter to 100-liter displacement (typically, more than 50 kW per cylinder output) featuring higher performance and controllability, greater reliability, and longer life, and much lower cost. Unique concentric dual-needle design with electro-hydraulic actuation and control.

• Heat rejection: while the higher compression of Westport HPDI 2.0 engines provide the heat necessary to auto-ignite their fuel, combustion in the Diesel thermodynamic cycle is more efficient, with more power and less heat produced than with the Otto thermodynamic cycle prevalent in SI engines. Westport HPDI engines operate at similar engine temperatures as diesel engines, reducing cooling challenges and reducing stress related reliability and durability challenges for other SI-based engine systems including turbochargers and exhaust treatment systems.

• Proprietary on-engine gas fuel conditioning module: Designed for more precise pressure control for even lower engine emissions and better fuel economy. New sealing designed for longer durability. Smaller size for ease of packaging on the engine.

• Redesigned electronic control systems: Allows full integration with existing engine and vehicle controls.

• Improved components: Completely reorganized supply chain allows for reduced production costs and increased scalability for manufacturing alongside existing diesel-based components for multiple OEMs. For example, the new gas control module (GCM) has been reduced in cost by approximately 60%.

• System performance: High transient performance with integrated fuel storage and delivery systems that ensure proper fuel flow under all driving conditions, improving performance, driveability, and safety at lower cost.

• Braking: By using the same high compression ratio as diesel engines, Westport HPDI engines deliver engine braking power equivalent to that of diesel engines which is critical in many trucking applications. The reduced compression ratio used in SI engines results in an approximately equivalent reduction in engine braking performance.

• Compatibility: Westport HPDI 2.0 is designed for complete compatibility with advanced commercial vehicles today. For example, by injecting fuel precisely into each cylinder, HPDI provides the same responsiveness and fast torque achievement as diesel engines, resulting in benefits such as an easier ability to be matched to automated manual transmissions (AMT).

• Improved emissions profile: Westport HPDI 2.0 is designed to meet Euro VI and EPA 2014 and is the only natural gas technology that can control methane emissions in-cylinder avoiding costly methane aftertreatment. As an added benefit, the significant increase in efficiency of HPDI over traditional SI engines affords Westport HPDI 2.0 lower greenhouse gas (GHG) emissions than conventional natural gas or diesel engines.

• Compliance and certification: In addition to the emissions certification for HPDI 2.0 engines, OEM vehicles built with Westport HPDI 2.0 technology will comply with applicable safety standards in North America—such as relevant Federal Motor Vehicle Safety Standards (FMVSS), National Fire Protection Association (NFPA), and Society of Automotive Engineers (SAE) standards—and their equivalents in Europe such as Regulation No. 110 of the Economic Commission for Europe of the United Nations (UN/ECE).

• Proprietary liquefied natural gas (LNG) tanks: Westport HPDI 2.0 LNG tank solutions range from 70 to 150 US gallons and up to 20,000 gallons for off road applications. The new tank configurations feature lower costs, high-quality testing and validation, and new designs for structures enabling several vehicle-mounting configurations including behind-the-cab gantry and frame-rail packages to simplify vehicle design and production. Westport has invested more than $1 million in HPDI 2.0 LNG tank testing and validation under extreme conditions to simulate the toughest environments for natural gas products.

• New proprietary intelligent LNG fuel pump: The redesigned cryogenic fuel pump is hydraulically driven and uses a single-stage, slow reciprocating architecture. This provides significantly lower cost, higher performance, and longer life and allows the use of fuel stations that deliver cold LNG, which improves vehicle range, and reduces station cost. The HPDI 2.0 fuel system is rated for delivering warm high pressure gas to truck engines with ratings up to 600 hp and to large off-highway engines up to 4,500 hp. Unlike traditional LNG systems, the full maximum flow rate is sustainable from the moment the truck is refilled to the moment the tank is empty. Because the pump is integrated into the tank module, there is no pump cool down time.

• CNG capability: Every natural gas engine burns compressed natural gas (CNG). Ultimately, the customer will decide which form of natural gas they wish to carry—either high pressure CNG or cold cryogenic LNG—based on a number of variables including but not limited to: weight of the load; weight of the fuel storage system; range required by the vehicle; and availability of CNG and LNG. The HPDI 2.0 system is architected to be compatible with LNG and CNG allowing the market to decide which storage method it prefers. Given the energy density of LNG compared with CNG, and Westport HPDI’s ability to haul heavier loads over longer distances as compared with traditional natural gas engines, in most cases we expect HPDI applications will select LNG fuel storage.

Westport first-generation HPDI systems have been delivered on more than 1,200 Peterbilt and Kenworth trucks since its first wide-scale introduction in 2010. As noted in previous news releases and customer communication, Westport is committed to the continuation of its class-leading support for all existing customers with the first generation of HPDI.

In partnership with Peterbilt and Kenworth dealers, Westport will be able to offer compatible next-generation system features to existing customers, as some HPDI 2.0 components are applicable to first generation HPDI. The benefits are expected to be reduced costs, improved components, and increased durability and performance. Further information is available from Westport representatives.

Westport designed HPDI 2.0 for simplicity, performance—and a reduction in overall system costs. For the first time, Westport expects OEM Westport HPDI vehicles to be competitively priced with SI-based systems.