Pure rapeseed oil could keep diesel engines running in low-emission zones

Researchers report that an ordinary diesel engine can be operated on pure rapeseed oil, using no fossil fuel, while producing far cleaner exhaust. If the approach proves workable at scale, it could allow millions of diesel cars and vans to keep driving into low-emission zones that looked set to exclude them.

Rapeseed oil gives diesel a second chance

Since the Dieselgate scandal, diesel has faced intense scrutiny, and many cities have set out plans to remove it from their streets. Even so, diesel powertrains are still widely chosen by long-distance motorists, farmers and fleet operators because they are hard-wearing and economical on fuel. Researchers at RUDN University, collaborating with European groups, have been looking for a route to preserve that efficiency while sharply reducing pollution.

Their newest results centre on a straightforward but bold swap: replacing conventional diesel fuel with pure rapeseed oil, a plant-derived fuel already well known through farming and food supply chains.

Pure rapeseed oil can power a conventional diesel engine when paired with targeted modifications, dramatically lowering fine particle emissions.

The team tested the idea using an MD-6 engine, a common type fitted to agricultural equipment. To cope with rapeseed oil’s greater thickness and viscosity, the engineers revised injection settings, altered fuel preheating, and refined combustion parameters. With these adjustments in place, the engine’s output and performance sat close to those seen on mineral diesel, while visible smoke and soot dropped markedly.

From cooking oil to climate tool

Rapeseed oil is classed as a first-generation biofuel, made from crops that are already widely cultivated across Europe, particularly in France and Germany. In contrast to fossil diesel, the CO₂ emitted during combustion of rapeseed biofuel is broadly comparable to the CO₂ the crop absorbed while growing, which can lower net greenhouse gas emissions when the production chain is properly managed.

However, the most immediate benefit is local air quality. When engines are tuned for this fuel, fine particulates and certain harmful hydrocarbons decrease substantially. That is especially relevant in major cities where public health bodies are prioritising the reduction of particulate pollution from road traffic.

Cleaner exhaust gases from rapeseed-fuelled engines could justify a better emissions rating and fresh access to low-emission zones for older diesel vehicles.

Heavy trucks show that the concept already works

This development builds on existing practice rather than starting from zero. In the heavy goods vehicle market, a comparable route has already been deployed using a commercial rapeseed-derived fuel: a 100% bio-based diesel sold in France as B100 and also marketed as Oléo100.

Use is concentrated among haulage firms, public bodies and bus operators. Operational experience indicates tailpipe fine particle emissions fall by about 80%, while fuel consumption rises by only around 5% versus standard diesel.

• Up to 80% fewer fine particles measured at the tailpipe
• About 5% extra fuel use due to lower energy density
• Engines retain similar pulling power and torque curves
• Infrastructure often limited to private depots and dedicated tanks

Leading truck makers-Renault Trucks, MAN, Volvo Trucks and Scania among them-already approve certain vehicles for B100. In France, those models can qualify for a Crit’Air 1 sticker, a category usually associated with newer petrol cars and hybrids. That classification helps them gain access to low-emission zones that are increasingly closed to older diesel vehicles.

What researchers did differently

RUDN’s group pushed the idea further by running on pure rapeseed oil rather than a processed ester-based blend. On paper, this could streamline supply: farmers or co-operatives could press rapeseed into oil and provide it more directly.

To make that realistic, the engineers concentrated on three technical fronts:

Challenge	Why it matters	Possible solution
Fuel viscosity	Rapeseed oil is thicker than diesel and can damage pumps and injectors.	Preheat the fuel and recalibrate injection timing and pressure.
Cold starting	At low temperatures, oil flows poorly and combusts badly.	Use electric heaters, insulated lines or blended fuel in winter.
Material compatibility	Rubber seals and plastics may not tolerate vegetable oil long term.	Use resistant materials and updated fuel-system components.

After resolving these issues during bench testing, the MD-6 ran reliably on pure rapeseed oil across changing load conditions. The next step is to confirm the findings through long-duration field testing and to assess passenger cars, where operating conditions vary far more.

Can private diesel cars really benefit?

The decisive challenge will be moving from laboratory success to everyday cars and light vans. Modern diesel cars rely on sophisticated high-pressure common-rail injection, exhaust aftertreatment such as particulate filters, and AdBlue-based selective catalytic reduction. Altering fuel properties can disrupt the finely tuned trade-offs between economy, drivability and legal emissions performance.

Turning existing diesel cars into rapeseed-fuel hybrids will require both mechanical updates and regulatory willingness to authorise them.

Researchers are therefore investigating injector behaviour with pure oil, the way filters respond to altered soot chemistry, and whether AdBlue dosing strategies need adjustment. Manufacturers would also have to demonstrate that durability requirements and warranty expectations can still be satisfied.

Rules are another limiting factor. In a number of European states, only Euro 6 vehicles-generally sold from about 2014 onwards-are permitted to use certain rapeseed-based fuels. Extending approvals to older but well-maintained vehicles would depend on new test methods and political support.

Fuel distribution: the missing link

At present, pure rapeseed fuel is barely available at public forecourts. Operators using B100 or comparable fuels typically depend on specialist suppliers delivering to private depot tanks. That arrangement suits fleets, but it does not meet the needs of private motorists who require widespread, dependable access.

To broaden availability, fuel companies would need to add extra storage capacity, modify dispensing equipment and revise safety procedures for vegetable-derived fuels. Retailers are unlikely to spend that money without consistent demand and a stable regulatory framework.

Some commentators argue for an incremental rollout: dual-fuel pumps providing both standard diesel and an approved rapeseed-based alternative, first focusing on rural regions where rapeseed is produced locally. Later, filling stations inside low-emission zones could introduce the fuel as part of wider air-quality initiatives.

What this could mean for diesel owners

Across Europe, millions of motorists drive diesels with plenty of mechanical life remaining, yet they face premature replacement as emissions policies tighten. A credible option to run on pure rapeseed oil could materially change those decisions.

Under a plausible scenario, a Euro 6 driver might pay a little more per litre and see slightly higher consumption per kilometre, but could still enter restricted areas using a more favourable emissions sticker. Local authorities would benefit from improved air quality without forcing rapid, large-scale scrappage of relatively modern vehicles.

Fleet owners could potentially move faster. A regional delivery firm might convert its entire Euro 6 diesel fleet to rapeseed-based fuel, secure a bulk supply agreement, and channel spending towards local agriculture. That would also reduce exposure to swings in fossil fuel prices and support climate pledges without needing to replace the whole fleet with electric vehicles immediately.

Key terms and practical risks

A few recurring technical terms shape the discussion:

• Particulate filter (DPF): an exhaust component that captures soot. Fuel choice can alter how frequently regeneration is required.
• AdBlue: a urea solution used to reduce nitrogen oxide emissions. Changing fuel characteristics may require different calibration.
• Euro standard: the European scheme setting maximum pollutant limits for new vehicles. Biofuel use can affect real-world outcomes.

Risks remain. Using pure rapeseed oil without the necessary engine changes can block injectors, worsen combustion and cause costly failures. Informal conversions that rely on recycled cooking oil already exist in some areas, illustrating both the potential and the drawbacks; without control and proper engineering, emissions can rise rather than fall.

Agriculture presents its own constraints. If demand for rapeseed fuel scales up, it must not undermine food production or encourage damaging land-use change. Policymakers will need to decide how much land can sensibly be allocated to energy crops while protecting food supply and biodiversity.

Where this breakthrough could lead next

A rapeseed-diesel hybrid approach could function as a transitional technology, delivering faster reductions in local pollution while electric and hydrogen infrastructure continues to grow. Some engineers even envisage combinations such as plug-in diesel hybrids running on biofuel, cutting both tailpipe emissions and fossil fuel dependence on long journeys.

For the moment, the RUDN bench tests indicate that diesel-often treated as incompatible with climate strategy-still has scope to evolve. If regulators, fuel suppliers and vehicle makers align, a crop with yellow flowers could influence the direction of millions of engines that seemed headed for early retirement.