Modified diesel engines running on rapeseed oil: the RUDN University study

A research team has caused a stir with modified diesel engines: suddenly the long-standing workhorse runs on rapeseed oil rather than fossil fuel.

A scientific project has reworked a conventional diesel engine so it can operate reliably on rapeseed oil. The study comes from Russia’s RUDN University and is already being hotly debated in specialist circles: could this kind of approach win back market share from electric mobility - or is it simply a smart niche solution for agriculture, haulage firms and developing countries?

What the engineers actually achieved

Diesel engines are widely regarded as tough, efficient and built to last. Their biggest drawback is simple: they burn traditional petroleum-based fuel. Researchers at RUDN University have therefore modified a standard diesel engine so it can be fuelled with rapeseed oil - a plant-based oil produced in large quantities across Europe.

At the heart of the work is a re-tuning of the entire injection and combustion process. Rapeseed oil is significantly more viscous, denser and less volatile than regular diesel. That means it atomises less effectively, mixes with air more slowly and burns differently. Without changes, the engine would run more roughly, use more fuel and produce heavier smoke.

"The researchers adjusted injection timing, injection pressure and the geometry of the injectors - only then does rapeseed oil become suitable for everyday use in a diesel engine."

This is exactly where the new development sits: through extensive test runs, the engineers searched for the best settings until the engine delivered performance on rapeseed oil that is comparable to operation on conventional diesel.

Why running engines on vegetable oil has been difficult until now

In theory, almost any vegetable oil can be burned. In practice, the hardware usually gets in the way. Rapeseed oil and other plant oils come with several disadvantages at once:

• high viscosity (in other words, thicker than diesel)
• poorer atomisation at the injector nozzle
• different ignition and combustion behaviour
• a tendency to form deposits in lines and nozzles

These characteristics can lead to:

• higher specific fuel consumption
• harsher engine running
• less favourable exhaust behaviour with more particulates

As a result, many attempts to run production diesel engines on vegetable oil “on a wing and a prayer” have ended with failed injection pumps, clogged filters and expensive repairs. According to the publication, this is precisely what the so-called Lomonosov project set out to reduce in a systematic way.

The technical tricks behind adapting a diesel engine to rapeseed oil

The RUDN engineers tackled multiple adjustment points in parallel. The most important levers included:

Earlier injection timing

Because rapeseed oil responds more slowly, the fuel needs to be injected slightly earlier. This leaves enough time for the fuel to mix with the air and ignite at the right moment. The researchers shifted the start of injection so the in-cylinder pressure curve once again resembles that of standard diesel operation.

Optimised injector nozzles

A second step focused on nozzle geometry. Small changes to the flow zone and the drilled holes affect how finely the oil is dispersed during injection. The finer the spray, the cleaner the combustion.

The study explains that revised nozzle geometry makes it possible to balance good atomisation, stable operation and an acceptable pressure level. This matters particularly for existing engines, which could potentially be converted with relatively straightforward modifications.

Blends of diesel and biofuel

Rather than relying exclusively on pure rapeseed oil, the engineers also tested mixtures. The results indicate that certain blends of mineral diesel and rapeseed oil can combine the strengths of both fuels.

• A higher bio content reduces the fossil CO₂ footprint.
• Keeping a portion of conventional diesel improves cold-start behaviour and stability.
• Emissions of nitrogen oxides and carbon monoxide can fall noticeably.

The best mixing ratios depend on engine design, the injection system and the intended duty cycle. A tractor running continuously needs different settings from a delivery van that faces frequent cold starts.

What this means for climate and air quality

Rapeseed oil is considered a first-generation biofuel. Its climate impact depends heavily on how the feedstock is grown and processed. In principle, greenhouse-gas emissions can be reduced significantly compared with purely fossil diesel - especially if the rapeseed is cultivated on existing arable land and co-products are used effectively.

The study points to several environmental upsides of the modified engines:

• less dependence on imported crude oil
• reductions in nitrogen oxides and carbon monoxide in the exhaust
• potential for closed regional material cycles, for example in agriculture

"For tractors, construction machinery and stationary generators in particular, rapeseed-oil diesel could act as a kind of ‘green transitional powertrain’ before everything is electrified."

For densely populated areas, fine particulate pollution remains a sensitive issue. Without a particulate filter, a rapeseed-oil diesel still emits soot. However, modern exhaust after-treatment can largely be transferred, meaning local air quality does not necessarily have to deteriorate.

Is rapeseed-oil diesel a threat to electric cars?

The big headline is: “The end of EVs?” In reality, this technology is more likely to complement than replace battery-electric vehicles. Electric drive and combustion using biofuels play to different strengths.

Aspect	Electric car	Rapeseed-oil diesel
Operating energy efficiency	very high	moderate
Range / refuelling time	dependent on charging infrastructure	fast refuelling, long ranges
Dependence on raw materials	rare metals, batteries	arable land, rapeseed production
Use in heavy equipment	still limited	strong position, proven technology

In cities with strict climate targets, authorities can hardly avoid electrification. Buses, delivery services and private cars with batteries suit short trips and predictable charging points. For heavy lorries on long-distance routes, construction machines in remote areas or agricultural equipment, electrification remains difficult and expensive even today.

This is where many experts see the main opportunity for such biofuel projects: they extend the usable life of existing diesel technology, cut its climate impact at the same time, and reduce reliance on fossil diesel.

Where this technology makes the most sense

Agriculture and local-authority fleets

Rapeseed is grown widely across Europe, often as part of crop rotation with cereals. Farmers could refuel with fuel sourced from their own region and become less exposed to volatile diesel prices. Local authorities operating depots for highways maintenance or winter service fleets could follow a similar approach.

Developing countries and remote regions

Where there is no reliable electricity grid, electric vehicles are hard to run. In such places, vegetable-oil diesel generator sets can power hospitals, refrigeration chains or pumping systems. If the oil is produced locally, more value creation stays in the country.

A bridging option for existing engines

Converting existing diesel engines is far cheaper than replacing an entire fleet. Businesses could keep vehicles in service for longer, operate them on rapeseed-oil blends and move gradually towards electric solutions once grid capacity and infrastructure are ready.

Environmental risks and unanswered questions

Biofuels do not automatically solve every problem. Rapeseed cultivation requires fertiliser, crop protection products and large areas of land. If demand rises sharply, displacement effects can follow: less land for food production, more monocultures and reduced biodiversity.

This is why policy makers and researchers discuss strict sustainability criteria, including:

• no cultivation on cleared forest land
• limits on monocultures
• clear CO₂ accounting that includes fertiliser and transport
• support for waste streams such as used cooking oil or plant residues

Another issue is maintenance and engine durability. If stored incorrectly, rapeseed oil can degrade faster and form gummy deposits. Workshops need experience, suitable filters and lubricants to prevent engine damage. Multi-year field trials will have to show just how robust the technology really is.

What drivers and fleet operators can take away

For the average car driver, little will change in the short term. Production cars under warranty are typically only allowed to use approved fuels - and pure rapeseed oil is rarely on that list. The research is far more relevant for operators of commercial vehicles that run for many hours each year.

For companies aiming to improve their CO₂ footprint, this could become another option on the table: not only batteries and synthetic e-fuels, but also specialised biofuels paired with adapted engine technology. In arid regions or countries with extensive agricultural land, this approach could offer a pragmatic route towards climate targets.

Anyone who digs into the topic quickly runs into terms such as “viscosity”, “start of injection” or “specific fuel consumption”. Put simply, the researchers are trying to tune the engine so that, despite a thicker fuel, it does the same job as before - only using a fuel that can be produced with a better climate profile. Whether that is enough to become serious competition for electric cars ultimately depends on policy, feedstock prices and the pace of charging-infrastructure expansion.