Diesel engines are the long-term success story for tractor power, and with no obvious competitors currently available their popularity is likely to continue for some time.
The first alternative to animal power was the steam engine which was used mainly on big farms for about 40 years until the early 1900s when tractors began to take over. The first tractors used spark ignition engines, burning petrol at first but soon changing to petrol for starting followed by kerosene for working.
Diesel powered tractors made their first appearance in the 1920s.
The diesel or compression ignition engine was a German invention, patented by Rudolf Diesel in 1893, but there was little interest in the idea until 1921 when the Benz company started building a two-cylinder diesel engine to power one of their trucks.
Benz, which later merged to form the company with the Mercedes-Benz brand name, began using the truck engine in their tractors in about 1922 and these were the first diesel powered tractors.
Most of the Benz engines were used in trucks and tractor production grew slowly during the 1920s, including a small number sold in Australia.
Small scale diesel tractor production in Germany and also in Italy continued during the 1920s, but the first of the major manufacturers to offer a diesel engine was Caterpillar in America.
They began developing an engine in 1929, with the production version available in their Sixty model in 1931.
It was America’s first diesel tractor and the world’s first diesel powered tracklayer, and it was also the most powerful diesel engine available in a tractor at that time, with 57kW (77hp) maximum output recorded when the Sixty tractor was tested at Nebraska.
One of the advantages claimed for diesel engines is their efficiency, measured by their ability to produce more power from each litre of fuel.
The Caterpillar Sixty was the first diesel tractor to be tested at Nebraska, where it produced easily the best fuel efficiency performance achieved by any tractor in more than 12 years of testing.
The Sixty engine was the start of Caterpillar’s long-term success as a leading maker of large capacity diesel engines.
The big surge in diesel popularity started after the end of World War II, with European companies leading the way helped by the relatively high cost of fuel and the diesel’s reputation for reduced fuel consumption.
Fuel efficiency remains an important factor in diesel engine popularity, and other attractions include good torque characteristics, and diesels avoid the need for spark plugs and some of the other electrical equipment that contributed to reliability problems on petrol/Kerosene tractors.
One of the companies that helped bring diesel power onto almost every farm was Perkins in Britain with their six-cylinder P6 engine.
Perkins, now a subsidiary of Caterpillar, developed the P6 in 1937 for powering trucks. The design included indirect injection and overhead valves, and one of its main attractions was easy starting.
While many of the other early diesels needed a small petrol engine to start the main power unit, the Perkins engine was started by a battery powered electric motor.
The first production tractor to be powered by the P6 was the Fordson Major built by the Ford company in Britain and available with a spark ignition engine from 1945, and with the diesel version offered as an option from 1948.
Adding the diesel engine increased the power output to 33kW (45hp) compared to the 20kW (27hp) maximum from the standard Fordson engine.
Massey-Harris was the next tractor company to specify the Perkins P6.
The Canadian based company was opening a new factory in Britain to build the 744PD tractor based on a North American design.
The original version was equipped with a petrol/kerosene engine for the Canadian and US markets, but diesel power was specified for tractors built in Europe.
After checking specifications and performance details for all the available diesel engines, Massey-Harris engineers chose the P6 from Perkins. The engine developed output of 34kW (46hp)
It remained the biggest selling Perkins engine until 1956, and an updated version of the engine was available until 1969 when the production total in Britain had reached more than 318,000 plus large numbers built under licence in Argentina and India.
Following the success of their first diesel powered tractor, Massey-Harris introduced the first diesel powered combine harvester in 1953.
This was the British built MH-780 powered by a 46kW (62hp) Perkins engine and equipped with a 3.66m working width. An Austin petrol/kerosene engine was available as an option.
The combine later changed its model number to MF-780 following the company name change from Massey-Harris to Massey Ferguson.
With fuel prices lower than in Europe, American farmers had less incentive to make the switch to diesel power, and this meant that some tractor manufacturers delayed the introduction of diesel models.
John Deere was one of the exceptions, starting their diesel development program during the early 1940s, with production beginning in 1949 when the Model R tractor was announced.
The engine for the Model R was based on the familiar horizontal twin-cylinder layout that had brought John Deere into the tractor market more than 30 years previously. While other companies had switched to more modern four and six-cylinder designs, John Deere had retained their two- cylinder layout.
Farmers appreciated the reliability and simplicity benefits of having fewer working parts with easier servicing access and the two-cylinder series was one of the most successful engine designs the tractor industry has produced.
The output of the Model R engine was 38kW (51hp), making it the most powerful tractor the company produced.
For easy operation, the tractor included a small petrol engine for starting the diesel, plus a battery powered motor for starting the petrol engine, but the petrol engine could also be started manually if the battery was flat. When the Model R was officially tested it set a new fuel efficiency record at Nebraska.
Sales of diesel powered tractors increased rapidly from the 1950s onwards, helped by rising fuel costs and by improvements in engine design and efficiency.
One of the most important technical advances was the addition of turbocharging to boost diesel engine power output and efficiency.
A turbocharger is a small turbine that rotates at high speeds and turns a compressor to increase the supply of air going into the combustion chamber. Increasing the air supply means more oxygen is available to burn extra fuel, making extra power available to increase the tractor’s work rate.
Turbocharging is unusual because it produces something for nothing. The turbine has a typical rotation speed of about 80,000 rpm and it is powered entirely by the waste energy in the stream of hot exhaust gases travelling from the combustion chamber.
Almost all current production tractors above about 74kW (100hp) now have a turbocharger because of the benefits it achieves.
Compared with naturally aspirated or non-turbo diesels there is typically a 25 per cent increase in power output, but the fuel efficiency is also improved because of changes in the combustion process and this also affects the exhaust emissions to reduce air pollution levels. Adding a turbo can also reduce engine noise because some of the energy released in the exhaust gases is absorbed by the turbine.
The first turbochargers arrived on farms in the mid-1960s when they were used on some American built forage harvester engines to increase the work rate.
Turbo tractor engines were available from about 1971, and the pioneers included the Ford 7000 model.
The turbo engine that produced 69kW (94hp) in the 7000 was basically the same as the naturally aspirated or non-turbo power unit in the smaller Ford 5000 tractor where the output was only 55kW (75hp).