Lifting the hood: engine and truck developments across the pond that will reach UK 09 August 2023

SuperTruck II Daimler Trucks North America

Five teams of US truck and engine manufacturers are nearing the end of SuperTruck II, a government-backed project to radically improve the efficiency of Class 8 articulated trucks — ‘18-wheelers’ running at a gcw of up to 80,000lb (36.3 tonnes), reports Toby Clark

When the project began in 2016, the US Department of Energy (DOE) said: “These trucks haul 80% of goods in the United States and use about 28 billion gallons of fuel per year, accounting for around 22% of total transportation energy usage… a significant opportunity for carbon emissions reduction and energy savings.” To put that into perspective, 28 billion US gallons is 106 billion litres, or around four times the total UK consumption of DERV.

Following on from the SuperTruck I programme, SuperTruck II gave around $20m of funding to each team, to be matched by the companies themselves. The aim was not simply to produce ‘concept’ vehicles, but to develop usable technologies which could be adopted in the short to medium term — so it specifically looked at diesel-powered trucks rather than electric or hydrogen power. The five teams are:

  • Daimler Trucks North America (DTNA), operating under the Freightliner and Detroit Powertrain brands
  • Paccar (DAF’s parent company) operating under the Kenworth brand
  • Cummins together with Peterbilt (another Paccar brand, but operating independently from the Paccar entry)
  • Navistar (part of VW subsidiary Traton, which owns MAN and Scania) under the International brand
  • Volvo Trucks USA
  • Each team has cooperated with a number of suppliers (for example, tyre, transmission, trailers and coatings manufacturers) and research bodies such as universities and national laboratories. In addition, some worked with potential operators: Cummins, for instance, with ‘customer counsel’ Walmart.

    The teams all presented interim findings last year, and two of them — DTNA and Navistar — have unveiled the finished vehicles along with further results. The basic targets set by the DOE were:

  • Greater than 100% improvement in vehicle freight efficiency (FE) on a US ton-mile-per-gallon basis,
  • relative to a 2009 baseline

  • Greater than or equal to 55% engine brake thermal efficiency (BTE) demonstrated at a constant 65mph on a dynamometer
  • Develop solutions that are cost-effective (Paccar defined this as having a three-year payback time).
  • One source quotes the 2009 baseline freight efficiency as 99 ton-miles per US gallon, although the targets are effectively slightly different for each manufacturer: while all are undertaken at an all-up weight of 65,000lb (29.5 tonnes), they use distinct routes — Freightliner’s, for example, is based on a 670km round trip on I-84 in Oregon, while Peterbilt uses a route in Texas based on Walmart’s duty cycle data.

    The participants also set themselves stretch targets: DTNA aimed for a 115% improvement in FE, while both Paccar and Volvo looked for a minimum of 120%, Cummins/Peterbilt 125%, and Navistar a stretch goal of 140%.

    The manufacturers, profiled below individually, have produced quite distinct vehicles, but some approaches taken are common to all: improved aerodynamics for tractor and trailer as a unit, the reduction of parasitic losses from ancillaries (usually employing a 48V ‘mild-hybrid’ setup with electrically driven ancillaries), careful thermal management of the engine and exhaust, and driver aids that encourage economical driving.


    DTNA reduced the aerodynamic drag of SuperTruck II by more than 12% over SuperTruck I, although the design was a refinement of the Freightliner Cascadia production truck. As well as the obvious smoothing of the bodywork, and rear-view cameras rather than mirrors, 'active side extenders’ and a roof spoiler close the trailer gap by up to 100mm at highway speeds, and ‘aerodynamic height control’ lowers the ride height.

    The 13-litre Detroit engine is built for torque at low revs — it reportedly runs at just 950rpm at highway speeds — with Miller-cycle intake timing, twin turbochargers in series and an intercooler between them. The ‘split cooling’ system has high- and low-temperature circuits, with a 48V electric water pump. DTNA is working on a phase change cooling (PCC) system for the high-temperature loop, which will use a 60/40 water-ethanol coolant and operate at 50bar to deliver waste heat recovery (WHR) via a three-cylinder, two-stroke expander.

    A ‘smart’ lubrication system uses a reduced volume of low-viscosity oil, ‘actively proportioning flow to the most sensitive components.’ Low-friction coatings and thermal barrier coatings in the engine and exhaust give further marginal gains: DTNA tested the engine at 52.9% BTE last year, and was confident of reaching 55%.

    The truck has ‘adaptive’ tandem axles, which automatically shift from 6x4 to 6x2 drive at highway speeds, with specially designed Michelin tyres, and a ‘dynamic load shift’ to transfer load from the drive axle to the tag axle, taking advantage of the tag tyre’s lower rolling resistance. Overall, the team claims that it has reduced the tractor rolling resistance by 12% over SuperTruck I.

    The Freightliner vehicle’s 48V electrics and lithium-ion batteries power features such as variable-rate electric power steering even while the engine is off in ‘EcoSail’ coasting mode. The electric air conditioning is said to consume 50% less energy than the system in Freightliner’s SuperTruck I.


    Paccar looked at an unusual gasoline compression ignition (GCI) engine at first, to combine high BTE with low NOx and particulate emissions. Later, however, it reverted to diesel. The MX-12 engine looks like a long-stroke development of the production 10.8-litre MX-11, with dual-loop cooling, two-stage turbocharging and dual high- and low-pressure intercoolers. With a comprehensive WHR system that even harvests heat from the lubricating oil, the firm suggests that it should hit the 55% BTE target.

    The 48V mild-hybrid architecture incorporates a 30kW motor/generator, and supports pre-heating for close-coupled exhaust aftertreatment said to meet California’s ultra-low 2027 NOx standards. It also offers ‘e-hoteling’ with electric air conditioning and a 48V heat pump.

    The truck itself promises to be rather futuristic: a highly aerodynamic tractor with central driving position, a narrow-track steer axle and enclosed wheels, plus a heavily faired trailer. Paccar suggests that a 170% FE improvement should be possible.


    Cummins and Peterbilt have claimed big improvements over the 2009 baseline truck: a 63% reduction in drag, 33% reduction in rolling resistance and overall weight savings of 2,100kg.

    The tractor has a central driving layout (described as ‘near-cabover-like’ by US journalists!) with an extremely curved windscreen. The trailer was made by Great Dane, and despite being almost 700kg lighter than standard, incorporates a solar panel roof. The tractor chassis also saves over 200kg by incorporating some aluminium components.

    The Cummins engine is not downsized, being based on the 14.9-litre X15. It’s a 48V ‘mild hybrid’ with electric ancillaries and a waste heat recovery system that incorporates a turbine expander built into the transmission. The baseline engine’s 46% BTE has been improved to 55% (with over 4% improvement coming from the WHR) and the overall improvement in FE is projected to be 170%.


    Navistar has just revealed its International-branded Supertruck’s final test results, with a 170% improvement in FE and a headline fuel economy figure of 16 miles per US gallon — that’s over 19mpg here. While details are sparse, the engine uses a BorgWarner WHR system, split cooling, the customary high-voltage (presumably 48V) mild-hybrid architecture and cylinder deactivation, and it has achieved 55.2% BTE on the dynamometer. The 6x4 tractor is matched to a streamlined composite trailer (also built by Navistar) with a fixed ‘boat tail’, for a combined kerbweight of 13,230kg — helped by a polycarbonate windscreen. Navistar also mentions ‘Vehicle-to-Everything’ (V2X) communications to help with efficiency.


    The SuperTruck I effort fed ideas directly into the subsequent VNL tractor, introduced in 2017, including aerodynamic chassis fairings, wheel covers and side skirts (dubbed the ‘FlowBelow Tractor AeroKit’), and the I-See predictive cruise control and gearshift system. However, the 11-litre engine proved a step too far and the VNL stayed with 13- and 15-litre options. This time, Volvo has presented a futuristic-looking vehicle, with electrically operated doors and steps, and touchscreen control of HVAC and other systems. It’s also a 48V mild hybrid (with features such as an electric EGR pump) but the 11-litre engine is rated at just 321bhp and — unlike the other tractors — the chassis is a 4x2 on 19.5in tyres. This helps toward the predicted 12.2t gcw total.


    The original SuperTruck programme started in 2009, set up by the Office of Energy Efficiency and Renewable Energy from the US Department of Energy (DOE). Four teams took part: Daimler Trucks North America (DTNA), Cummins & Peterbilt (jointly), Navistar and Volvo Trucks. Each were supported by a multi-million-dollar grant, which they had to match. Each team presented their results in 2015.

    The primary aim of SuperTruck I was to improve vehicle freight efficiency (FE) by 50% compared with a baseline 2009 truck: this figure is measured in units of US ton-miles per gallon, so it can be improved by increasing payload or reducing fuel consumption. In doing so, the idea was to identify technologies that would be viable in the market within two to four years (2017-2019) and five to ten years (2020-2025).

    In the end, these technologies included some that were already being seen on European trucks, such as predictive gear shifting, coasting (or ‘sailing’) on downhill sections, low-rolling resistance tyres and aerodynamic trailer fairings and skirts. But other innovations are only now appearing, such as waste heat recovery (WHR) systems, active aerodynamics and electrified engine ancillaries. Weight saving was also a focus, despite the addition of some extra equipment. Overall kerbweight (for tractor and trailer together) was typically reduced by around 500kg.


    Obviously, the SuperTruck projects’ achievements are not directly translatable to European conditions: the tractor units are all extra-long designs with ‘anteater’ bonnets, each gcw is low by European standards, the emissions standards are divergent and the road conditions are thoroughly different. In particular, lowering cruising speeds from 65mph to a European level would be a sure-fire way of improving fuel efficiency significantly.

    But as a demonstration of the progress that manufacturers can make — given the right incentives and competition — they are impressive. At the recent unveiling of the Navistar truck, Dean Opperman, chief engineer, advanced vehicle technologies, said: “Our goal is to continue to advance internal combustion engine technology as efficiently and sustainably as possible until there is parity with zero-emissions vehicles.” Many of the developments, such as electric ancillaries, predictive driving aids, weight reduction and aerodynamic improvements, will be equally applicable to future vehicles, whatever their power source.

    And there’s more to come, as the US government has already awarded $127m of grants for SuperTruck III, focusing on reducing emissions and improving medium- and heavy-duty truck efficiencies. Teams are Paccar, Volvo Group, Daimler Trucks, Ford Motor Company and General Motors. The programme is funded until late 2026.

    Toby Clark

    Related Companies
    Volvo Trucks Belgium NV

    This material is protected by MA Business copyright
    See Terms and Conditions.
    One-off usage is permitted but bulk copying is not.
    For multiple copies contact the sales team.