HarvestersRape­seed oil as an alter­na­tive fuel in forestry and agri­cul­ture

Harvesters are the Swiss Army knives of forestry. In just a few steps, they fell trees, remove branches, and prepare the timber for further processing. As they assume a key role in the forest, reli­a­bility is crucial – year-round, and in all condi­tions. In the Bavarian State Forestry forests, machines typi­cally run for more than 10,000 oper­ating hours before being retired from service. What is not visible is how one of these harvesters oper­ates on rape­seed oil fuel.

Known as the Rapster, it runs on rape­seed oil instead of diesel. This machine is part of a research initia­tive funded by the Bavarian Ministry of Economic Affairs, which aims to reduce green­house gas emis­sions in forestry oper­a­tions.

John Deere’s Euro­pean Tech­nology Inno­va­tion Centre (ETIC), in collab­o­ra­tion with the forestry equip­ment dealer Donauwald Forstmaschinen and the Tech­nology and Support Centre at the Compe­tence Centre for Renew­able Resources (TFZ), retro­fitted a G-series harvester to run on rape­seed oil. The Bavarian State Forestry then conducted prac­tical tests to assess its func­tion­ality.

The goal: a climate-neutral forestry machine

The char­ac­ter­is­tics of rape­seed oil fuel were a key issue during the harvester’s conver­sion. It is thicker than diesel, has different combus­tion char­ac­ter­is­tics, and needs to be preheated for optimal perfor­mance. “The heater of the harvester was orig­i­nally intended solely for heating the hydraulic system and the operator’s compart­ment,” explains Dr. Edgar Remmele, scien­tist at the TFZ. “John Deere has enhanced the func­tion so that the parking heater now addi­tion­ally preheats the rape­seed oil fuel tank and the engine block. This ensures that the engine starts reli­ably even at low temper­a­tures.”

Addi­tion­ally, the Rapster received a more powerful fuel pre-feed pump, heated fuel lines, and filters. These steps ensured that the rape­seed oil flowed well through the machine. “Even at -25°C, the harvester started up, while our diesel machines broke down one after another. That really impressed me.”

Rape­seed oil has not yet been approved for use in auxil­iary heaters, so the harvester was fitted with a sepa­rate 40-litre diesel tank for those func­tions. Once up to oper­ating temper­a­ture, Friedl switched to rape­seed oil for the main drive. The exhaust aftertreat­ment system also requires a brief diesel supply for particle filter regen­er­a­tion. “Theo­ret­i­cally, the contin­uous soot burn-off is so effec­tive that a soot filter regen­er­a­tion would hardly have been neces­sary,” explains Friedl. “The engine and the exhaust gas aftertreat­ment system oper­ated without any faults.” The partic­u­late and gaseous emis­sions were below the limits for a Stage IV machine.” Even the diesel used was renew­able and made from recy­cled frying fat. The harvester’s chain grease was also biodegrad­able.

Fewer green­house gases with the same power

The TFZ assessed the machine’s emis­sions during actual oper­a­tion. “The Rapster’s CO₂ savings are signif­i­cant,” says Remmele. “Throughout the machine’s entire service life, we reduced approx­i­mately 570 tonnes of CO₂ equiv­a­lents. This is equiv­a­lent to the CO₂ emis­sions of about 125 diesel cars annu­ally. Beyond emis­sions, there were other prac­tical bene­fits. Some of the managed forest areas were in water protec­tion zones where diesel-powered machines are restricted.

“Since rape­seed oil is not clas­si­fied as a hazardous substance, we oper­ated and parked the harvester easily in areas where diesel-powered machines are not permitted. Refu­elling wasn’t a problem either – I always had a trailer with 1,000 litres of stan­dard­ised rape­seed oil with me, which I could leave anywhere without any prob­lems.”

The Rapster’s perfor­mance and consump­tion hardly differ from diesel oper­a­tion. Despite rape­seed oil’s lower energy density, the machine’s injec­tion settings were adjusted to main­tain full power.

“With approx­i­mately 1.16 litres per cubic metre of wood, consump­tion remained average,” says Friedl. “The machine effort­lessly managed long oper­a­tions lasting up to eight hours without any issues. The only differ­ence is that the tank should always be full in the evening to prevent conden­sa­tion. “Mois­ture can condense in the tank, espe­cially at low temper­a­tures, which can degrade the fuel prop­er­ties and clog fuel filters.”

Rape­seed oil-based fuel possible for other machinery

The same fuel was tested on a John Deere 8R tractor, which is based on the harvester’s engine plat­form. It too ran smoothly, proving that rape­seed oil can power a broader range of diesel-based machinery.

Although rape­seed oil has distinct ecolog­ical advan­tages over diesel, adop­tion remains slow. Econom­i­cally, there’s little incen­tive to switch as diesel is taxed more favourably for agri­cul­ture and forestry. Plus, a lack of clear polit­ical support and manu­fac­turer approvals continues to limit uptake.

The Rapster research project has been fully completed and continued to operate with rape­seed oil beyond the actual project dura­tion. After over 11,000 oper­ating hours, the Bavarian State Forestry is now selling the machine.

Remmele summarises satis­fac­to­rily: “I think our project has demon­strated throughout the machine’s service life that the tech­nology works and that rape­seed oil fuel can be a reli­able alter­na­tive to diesel.”