Prevost prepares for new emissions standards with extensively revised Volvo D13

Prevost, the Volvo Group’s North American premium motorcoach manufacturer, has taken another important step in preparing for the next emissions regulations: the upgraded version of the Volvo D13 diesel engine developed to meet EPA 2027 requirements has received certification from the U.S. Environmental Protection Agency (EPA) and the California Air Resources Board (CARB). The new rules will bring a major tightening for North American heavy-duty vehicles, reducing the permitted nitrogen oxide emissions limit by more than 80 percent compared with the current level.

Thanks to the certification, Prevost buses equipped with the new powertrain for the 2028 model year will be eligible for registration in every U.S. state, including California and the states that voluntarily apply CARB regulations. The same engine version can also be used in Canada, meaning the manufacturer will not have to maintain different emissions specifications for different parts of the North American market.

Nearly two decades with Volvo engines

One of the defining turning points in the history of Prevost, which has Canadian roots, came in 1995, when Volvo Bus Corporation and the British Henlys Group jointly acquired the company from its previous Canadian-American owners. The arrival of the Swedish vehicle-industry group not only provided strong financial backing, but also gave Prevost access to Volvo’s development, research and manufacturing expertise. Full ownership of Prevost eventually passed to the Volvo Group in 2004, after the financially troubled Henlys exited the ownership structure.

At the same time, Prevost is not simply building a North American body on a Volvo bus chassis. The H3-45 and X3 series are integral coaches of the company’s own design, into which powertrain components sourced from the Volvo Group are installed separately. One of the most important of these is the Volvo D13 engine, which appeared in the Prevost range in 2008 and became the exclusive engine in the manufacturer’s coaches from 2010. Volvo technology has also appeared in other areas, including the addition of the I-Shift automated transmission to the lineup.

The relationship between the two brands is also visible in the opposite direction: the Volvo 9700 coach for the North American market has likewise been present on the continent since 2009, while Prevost has become a key player in the Volvo Group’s North American premium coach operations.

Not a new engine, but an upgraded D13

To meet EPA 2027 requirements, Volvo has not developed a completely new engine, but has carried forward the well-proven D13 engine family. The 13-liter base engine has remained essentially unchanged, while the associated emissions aftertreatment, electrical, air-supply and cooling systems have been significantly revised.

The D13 used in the Prevost H3-45 is an inline six-cylinder, common-rail diesel engine with a variable-geometry turbocharger. The 13-liter engine has a bore of 131 millimeters and a stroke of 158 millimeters, with a compression ratio of 17:1. Its maximum output is 435 horsepower, or around 324 kW, while peak torque is 1,700 lb-ft, approximately 2,305 Nm. Its dry weight with full equipment is 2,605 pounds, or about 1,182 kilograms.

The Volvo Group subjected the EPA 2027-specification D13 and its associated emissions aftertreatment system to an extensive validation program: during development, more than 2.5 million miles, or around four million kilometers, of testing were completed under laboratory and real-world road conditions.

Emissions aftertreatment brought into a single unit

In terms of its technical layout, the EPA 2027 D13’s emissions aftertreatment follows in many respects the solutions familiar from Euro VI diesel engines in Europe, using both a particulate filter and an SCR system. To meet U.S. requirements, however, Volvo has further developed the aftertreatment system and integrated it into a single compact unit, with a dedicated 48-volt system also helping to keep it at the correct operating temperature.

Accordingly, one of the most significant changes is the new so-called one-box exhaust aftertreatment system. Instead of the previous multi-unit arrangement, the main elements of the emissions aftertreatment have been integrated into one compact module. This not only simplifies the system’s layout, but also makes maintenance points easier to access, which Prevost says can result in faster troubleshooting and shorter service times.

The new unit is also around 50 pounds, or nearly 23 kilograms, lighter than the previous solution. In designing the layout, particular attention was paid to ensuring that the system’s key service points can be reached from ground level.

Operation of the emissions aftertreatment system is also supported by a new 48-volt generator. This is specifically intended to supply electrical power to the one-box unit and helps the aftertreatment system reach and maintain the proper temperature under varying operating conditions. This is one of the key prerequisites for meeting increasingly strict nitrogen oxide limits.

Revised cooling and air supply

The changes do not end with exhaust aftertreatment. A newly designed air filter system is used, with a filter element that can be replaced without tools. The role of the more compact system is to provide the D13 with sufficiently clean, low-temperature air while making regular maintenance simpler.

Charge-air cooling has also been revised. The new U-flow charge-air cooler works with a separate cooling radiator and new stainless-steel coolant lines. The aim of the modification is to ensure a lower intake-air temperature, which benefits both engine efficiency and performance, while the stainless-steel lines offer better corrosion resistance over the long term.

The expansion tank has also received a new design. The one-piece, translucent tank is located at a height of about 5.2 feet, or roughly 1.6 meters, allowing the fluid level to be checked directly without any additional equipment. The solution itself is not entirely new: Volvo has been using it in series production in other applications since 2022.

The location of the air dryer has also been changed. The unit has been moved to a standardized, more easily accessible position in the engine compartment. This is one of the smaller design modifications with which the manufacturer primarily aimed to improve serviceability and reduce downtime.

NOx limit more than 80 percent stricter

The development is driven by the next step in U.S. heavy-duty vehicle emissions regulation. The EPA 2027 rules require permitted nitrogen oxide emissions to be more than 80 percent lower than under the current requirements. Compliance with California’s CARB requirements is especially important because, in addition to California, several other U.S. states apply or adopt the organization’s stricter emissions standards.

For Prevost, it was therefore an important consideration that it should not have to offer different powertrains for different markets. The new D13, certified by both the EPA and CARB, will be usable in all 50 U.S. states, as well as in Canada’s ten provinces and three territories.

For Prevost, the transition to the new emissions regulations therefore does not mean a complete change of powertrain. The manufacturer is retaining the basic architecture of the D13, used for nearly two decades, and its 13-liter displacement, while primarily redesigning the systems that support the engine. This may be particularly advantageous for operators and service organizations, as the familiar engine family, its basic layout and existing service experience can continue to be used while meeting the new emissions requirements.