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Alike but Different: On vs Off-Road Engines and Equipment

    There’s no outward resemblance of an 18-wheeler to a farm tractor, construction machine,  locomotive, or tugboat. But look closely and you’ll find that these all are predominately powered by diesel. More than 76% of commercial trucks and more than 96% of the largest tractor-trailer sized big rigs on the road are powered by diesel. It’s also the prime power for off-road engines and equipment like that used in the construction, agriculture, marine and rail sectors. As for fuel, any diesel engine old or new, on or off-road can use renewable low carbon and biodiesel fuels right now just like regular diesel. But that’s where the similarities end.

    The population of off-road engines and equipment is relatively large in number, generally older with slower turnover, diverse in nature, and fundamentally different in the type of operation compared to on-road diesel vehicles. Consider the diversity in function and size in farm tractors and machines, construction equipment, industrial engines, and generators compared to commercial trucks.

    Far fewer new off-road engines and equipment are produced each year; on the order of several thousand across each of the most popular engine ranges and categories. Compare to the on-road sector, where heavy-duty truck makers are on track to produce about 250,000 to 300,000 trucks/engines this year in the large truck segment alone.

    Equipment turnover is generally higher in the on-road trucking sector, due to the large number of miles traveled per year. Currently 53% of all registered commercial trucks operating are model year 2010 and newer, equipped with the latest technology for near-zero emissions performance.

    In the off-road sector, there is considerable variability in the ages and emissions generations in use. Older generations of equipment still exist but typically is used in far fewer hours. Off-road equipment in the construction sector like popular backhoes might turnover faster than large excavators. Of course, the agriculture, marine, rail, and power generation segments all have their own profiles of new equipment acquisitions, turnover, and replacement.

    In the trucking sector, engine choices and size/displacements fall in a narrow range – generally between 175 and 600 horsepower. But in off-road engines and equipment, the range varies from a few horsepower in small mobile machinery to several thousand horsepower in power generation, marine, and rail applications.

    On-road commercial trucks travel an average of 100,000 miles annually with a large portion of that time at highway speeds in steady state operation, optimized for low fuel consumption. Off-road engines and equipment utilization varies substantially, with some only operating a few hundred hours a year depending on specific job demands. Most off-road engines operate less in steady-state operating modes, more having a mix of power demands depending on the task at hand. For example, lifting a heavy load for a few minutes by crane or a wheel loader requires high power. A wheel loader may be in a repetitive motion state moving aggregate (stones) from a pile to load a truck, followed by an extended idle state.

    As much as the differences in the on and off-road sectors define them, they share a common trajectory that has led to the diesel engines that power them being able to achieve near zero emissions levels and utilize low-carbon renewable and biodiesel fuels. Because of the great diversity in their design and duty cycles, the on and off-road sectors are different in the consideration of the use of alternative fuels or electrification. For example, local pickup and delivery trucks that haul generally lighter loads and travel relatively short ranges with return to base patterns that enable access to charging infrastructure are well-suited for electrification. In the off-road sector, smaller compact construction equipment is emerging as a segment potentially more suited for electrification because of the types of jobs it is used for that may be for short duration or relatively low power demand.

    Larger construction machinery, with high power demands and typically longer durations of operation, is less suitable for electrification on a wide scale given the state of technology today. For some of these applications, manufacturers are exploring the use of hydrogen-fueled internal combustion engines as an alternative to diesel. But considering that much off-road equipment including farm equipment and construction machinery works in remote locations without access to unique fueling infrastructure needed for charging batteries, they may not be very suitable for electrification.

    Alternatives to diesel are emerging in both the on and off-road sectors. Their adoption by consumers will depend on a range of factors including performance, refueling, cost, durability and reliability compared to diesel. Given the vast diversity of engines and equipment in the off-road sector and their performance requirements, diesel is expected to remain the predominate power technology used in the majority of off-road applications for the near future. 

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