FreightWaves and FreightWaves SONAR, the industry-leading freight forecasting platform, closely monitor and report on the supply and price of diesel in 135 markets. At this time, it is the fuel that drives the U.S. trucking industry.
It is unlikely that there are many Class 8 truck drivers still driving that ever drove trucks powered by gasoline; most gasoline-powered engines had been phased out by the mid-1950s when diesel engines replaced them.
Early history of the diesel engine
The Industrial Revolution began in the 1790s and by the 1880s and 1890s, it was changing the world. One consequence of the Industrial Revolution was that more and more people were working in manufacturing and industrial facilities and fewer were working in agriculture. At that time, the steam engine was the predominant power source for large industries, and railroad locomotives were steam-powered.
Rudolf Diesel, a Frenchman, began developing a compression ignition engine in his Paris workshop in 1885. Over the course of 13 years he received a number of patents for his invention of an efficient, slow-burning, compression ignition, internal combustion engine that was named for him. From 1893 to 1897, Diesel further developed his ideas at a company that eventually became MAN, which is now part of TRATON SE. In addition to MAN, a Swiss firm, Sulzer Brothers, bought certain rights to Diesel’s invention in 1893.
Early diesel engines were quite large and could only operate at low speeds due to limitations caused by their compressed air-assisted fuel injection systems. Concurrently, the diesel engine was competing with another engine concept – the hot-bulb engine invented by Akroyd-Stuart.
Diesel’s engine needed more work to become commercially viable. A number of other engineers and developers joined the effort to improve the market potential of Diesel’s idea.
Diesel’s attempts to promote the engine before it was market-ready led him to suffer a nervous breakdown. In 1913, Diesel was deeply troubled and financially insecure. He vanished from a ship on a voyage to England; whether he was murdered or committed suicide has never been fully established. After Diesel’s patents began to expire, several companies further developed diesel engine concepts.
How a diesel engine is different from a gasoline engine
Gasoline-powered engines need a ‘spark’ from a spark plug. In a diesel engine, fuel ignition takes place without any spark as a result of compression of the inlet air mixture and then the injection of fuel. Diesel engines are now widely used because of their higher thermodynamic efficiency, which also leads to greater fuel efficiency.
Diesel engines are in widespread use
Today, diesel fuel is widely used in most modes of transportation, and diesel engines are found in a wide variety of machinery and vehicles. Some examples include:
Aircraft – the first diesel-powered flight of a fixed-wing aircraft took place on September 18, 1928. Diesel engines were used in airships and some aircraft in the late 1920s and 1930s, but were never widely used. On March 4, 1936, the airship LZ 129 Hindenburg, the biggest aircraft ever made, lifted off for the first time. The Hindenburg was powered by four V16 Daimler-Benz LOF 6 diesel engines. However, the one mode of transport in which the use of diesel engines is not widespread is aircraft.
Automobiles – while gasoline-powered automobiles dominate the U.S. market (and some others as well), diesel-powered automobiles are used across the globe. The first passenger car equipped with a diesel engine was produced in 1929. It had an Otto engine modified to use the diesel principle and a Bosch injection pump. Production of the first mass-produced passenger car with a diesel engine, the Mercedes-Benz 260 D, began in 1936.
(Photo: National Museum of American History)
Construction and agricultural equipment – diesel engines’ reliability, efficiency and greater torque make them the engine of choice for large construction equipment. In addition, diesel engines are used in a variety of the heavier tractors and other agricultural vehicles because of their durability and efficiency. Gasoline-powered engines are the norm for lighter agricultural equipment (such as lawn mowers and tractors). In 1923, at the Königsberg DLG exhibition, the first agricultural tractor with a diesel engine, the prototype Benz-Sendling S6, was introduced. Sendling began mass-producing a diesel-powered agricultural tractor in 1925.
Generators – many generators use diesel as a fuel, particularly in emergency situations when a generator is used for extended time periods.
Marine vessels – from cruise and cargo ships to privately owned leisure boats, many marine vessels use diesel engines. Reciprocating diesel engines are used because of their fuel economy and operating simplicity. In addition, their capacity to power larger vehicles makes them a popular choice for ships and boats. Because of global restrictions, new versions of diesel-based fuel for ships contain lower levels of sulfur (0.5%) as of January 1, 2020. In 1912, the Selandia became the first ocean-going ship equipped with diesel engines. The next year, NELSECO diesels were installed on commercial ships and U.S. Navy submarines.
Military vehicles – armored vehicles are powered by diesel engines and use diesel fuel because it is less flammable than gasoline. Diesel engines also produce higher torque and are less likely to stall. In 1937 Konstantin Fyodorovich Chelpan developed the V-2 diesel engine, which was used later in Soviet T-34 tanks, which are widely regarded as the best tank chassis of World War II.
Railroad locomotives – diesel replaced coal and fuel oil for steam-powered vehicles in the latter half of the 20th century. Diesel-powered locomotives are in use across the world in areas where track electrification is not feasible. Diesels are the engine of choice for freight trains that haul heavier loads. The first locomotive with a diesel engine was used on the Swiss Winterthur-Romanshorn railroad in 1912. The Budd Company built the first diesel-electric passenger train in the U.S. in 1934.
Trucks and buses – From the time that heavy-duty trucks began to be mass-produced in volume (shortly after World War I) and the early 1950s, most U.S.-built trucks were powered by gasoline engines. Beginning in the 1930s, many German trucks, buses and automobiles were powered by diesel.
Now, most trucks are diesel-powered (but many buses are powered by natural gas or electricity). The vast majority of Class 8 (heavy-duty) trucks in the U.S. and most parts of the world are powered by diesel-fueled engines. It was in 1908 that the first truck with a diesel engine was produced. In 1938, General Motors formed the GM Diesel Division (which later became Detroit Diesel) and introduced the Series 71 inline high-speed, medium-horsepower two-stroke engine. It was suitable for road vehicles as well as marine use. From 1962 to 1965, a diesel compression braking system (nicknamed the “Jake Brake”) was invented and patented by Clessie Cummins.
After World War II it took U.S. truck manufacturers a few years to create new designs and to re-tool. So when a new generation of heavy-duty trucks took to the highways in the 1950s, diesel engines began to overtake gasoline engines in heavy-duty trucking.
One reason was that a number of gasoline-powered engines could generate 1,800-pound feet of torque. One in particular was the OHC hemispherical combustion chamber Hall-Scott 1081-cubic inch straight six. But it cost as much to build as a diesel engine. And particularly at that time, diesel fuel was much cheaper than gasoline. Moreover, diesel fuel delivered better average fuel economy because diesel generates more heat energy per gallon (BTUs) than gasoline. So the primary reasons that truck manufacturers converted production from gasoline to diesel engines was that diesel fuel was cheaper and also generated more energy.
Numerous trucks hauling freight on an American highway. (Photo: saferoads.org)
How is the diesel engine different from the gasoline engine?
Here are some of the key reasons why the U.S. truck industry transitioned from gasoline-powered engines to diesel-powered engines in the 1950s.
Diesel fuel produces more energy than gasoline. Diesel produces about 147,000 BTU of energy while gas only produces about 125,000 BTU of energy. So for every drop of fuel used, diesel produces more energy than gasoline, and therefore a truck does not require as much diesel as it would require gas to carry the same load from point A to point B.
In addition, diesel engines can operate for around 12,000 to 30,000 hours before needing maintenance, while gas-powered engines can only run an average of 6,000-10,000 hours before maintenance is necessary.
Therefore, a diesel-powered truck can travel greater distances for an extended period of time, while also needing less maintenance than a gasoline-powered engine.
Because of federal and state fuel taxes, diesel fuel is now more expensive than gasoline. However, since diesel fuel is more efficient than gasoline (again, diesel produces more energy than gasoline), diesel generates better mileage overall and allows a truck driver to drive further between fill-ups. There are also significant maintenance savings.
A diesel engine does not require spark plugs to begin engine combustion. Since spark plugs need to be regularly replaced in gasoline-powered engines, this means that the maintenance costs of gasoline engines are higher.
Power To Weight Ratio
Heavy-duty trucks obviously have to be able to haul heavy loads across all types of terrain. These trucks require engines and fuels that produce high levels of torque. A diesel engine and diesel fuel produce the amount of torque needed by trucks, and also allow the engine to have a higher power-to-weight ratio.
Diesel engines have longer crankshafts than gasoline engines (to compress air for combustion).
The longer crankshaft produces a longer stroke. The longer stroke allows a diesel engine to produce higher torque. It is that torque that gives a diesel engine a higher power-to-weight ratio.
Navistar’s International LoadStar. Photo courtesy of Navistar
Life expectancy of diesel engines
While heavy-duty trucks require a great deal of ongoing maintenance (because of the heavy loads that they carry and the long distances driven), a diesel engine does not require as much maintenance as a gasoline-powered engine.
The reason is that gasoline-powered engines emit more heat than diesel engines. The heat causes metals in the engine to wear faster, leading to a shorter lifespan for gasoline engines than diesel engines.
Trucks on the highway, moving America’s goods. (Photo: Jim Allen/FreightWaves)
Thanks to Rudolf Diesel and others who came after him, diesel engines have powered equipment of many types throughout the world for a century. The importance of the diesel engine to global transportation is immeasurable. However, alternate forms of energy (electricity, natural gas, etc.) are being used more frequently, and may surpass diesel at some point in the future.
FreightWaves thanks CentralDiesel.com, Evan Transport, Inc., TruckFreighter.com and Wikipedia for information that contributed to this article.