The Diesel Hybrid and the Human Scale of Mobility

by Jim Lane (Biofuels Digest) ... That is a useful way to think about mobility, and a useful way to think about renewable diesel and the diesel hybrid technology. It disappeared from the United States after VW’s DieselGate, so we headed to Europe to test how RD does as a human experience and addressing the aspirations of a low-carbon economy.

The BMW X1 xDrive20d was carrying two people and roughly 200 pounds of luggage. It was running its air-conditioning through the August heat, climbing hills and descending hairpins. Our working route distance, including a modest allowance for missed turns, town circulation, fuel stops and comfort breaks, was approximately 1,406–1,416 kilometres.

That works out to approximately 4.85 litres per 100 kilometres, or 48–49 miles per American gallon.

BMW lists the X1 xDrive20d’s tank at 54 litres. After one refuelling, the dashboard projected 1,250 kilometres of range. That implied approximately 4.32 litres per 100 kilometres. Under the real conditions we encountered, the equivalent full-tank range was closer to 1,110 kilometres.

The dashboard was optimistic by roughly 12–13 percent. That is a surprisingly small difference for a loaded crossover travelling through mountains, towns, traffic and August heat.

The important point is that this was not a laboratory result. It was a real journey, with hills, luggage, air-conditioning and a driver who wanted to arrive while there was still a day left to enjoy.

The electric car would use less energy. That is not in dispute. But its advantage is often stated at the wrong boundary.

A battery is extraordinarily efficient at turning stored electricity into motion. Yet the battery must also carry the energy required for the journey. A 54-litre diesel tank contains far more usable journey energy than a similarly sized crossover battery, without adding hundreds of kilograms. That difference matters under sustained motorway speeds, high payloads, mountains, heat and uncertain charging access.

The relevant measure is not simply energy conversion. It is the whole duty cycle.

In ideal conditions, an electric crossover might make the journey with two charging sessions. In prudent real-world conditions, it might require three. Tropea’s final 34 kilometres are hilly and winding. There is no convenient charger waiting at the end. The car would need to preserve enough energy to descend into Tropea, spend the night without charging and climb back to the network.

Our normal lunch stop is about thirty minutes. It is not a lazy hour under a shady bough. It is a crowded service area, glaring sun, nowhere to sit and an overheated car whose air-conditioning must remain on. A fast charger could overlap with lunch—if it were immediately available. If there were a queue, lunch would become an hour or more of waiting.

The old orthodoxy said, “You must use gasoline.” Diesel survived because reality kept producing jobs that gasoline performed less well: heavy loads, long distances, ships, trucks, generators and rural machinery.

Dieselgate then revealed something worse than bad engineering: deliberate deception. Volkswagen lied. The punishment was deserved.

But one company’s fraud should not condemn every application of compression ignition forever. Nor should electric propulsion become a universal command issued without regard to driver, road, destination, payload, weather, charging access or daylight.

A modern diesel hybrid need not imply a return to fossil diesel. Renewable diesel made from waste fats, oils and residues—HVO, including HEFA-derived pathways—can preserve the vehicle and fuelling infrastructure while changing the carbon pathway. The machine remains familiar; the fuel becomes progressively less dependent on fossil carbon.

This is where the diesel hybrid becomes more interesting than either side of the usual argument. It is not the old diesel, and it is not an alternative to electrification everywhere. It is a platform for matching propulsion to duty cycle.

Let the urban commuter choose electric. Let the household with dependable home charging choose electric. Let fleets optimize their depot-based routes. But let the one-driver family crossing a country with luggage, hills, uncertain chargers and a finite daylight window choose the machine that preserves the day—possibly running on renewable drop-in fuel.

Policymakers should set stringent real-world emissions standards, measure lifecycle carbon and let technologies compete by duty cycle. Support charging where vehicles routinely dwell. Support renewable liquid fuels where energy density and rapid replenishment remain valuable. Decarbonize the journey without abolishing the journey. READ MORE