THE CASE FOR OIL BURNERS

FUEL ECONOMY

There are many reasons why diesel-engined vehicles achieve better fuel economy than their petrol equivalents. The fact that diesel fuel is more energy dense per litre is a good start, but the main reasons are that diesel has a higher compression ratio, which is thermally more efficient; and, unlike petrol engines that need to control the intake air volume (throttle) to achieve the stoichiometric (ideal) air-fuel ratio of 14,7 to 1, diesel engines run “un-throttled” and that means there are less pumping loss during part-load conditions to get fresh air inside the combustion chambers.

Another advantage of high fuel efficiency is that less CO is produced. If manufacturers plan to meet the low fleet-average targets in Europe of 95 g of CO per kilometre by 2020, but still use ICE, diesel will have to be part of the plan.

DIESEL FUEL

Refining crude oil (the most common method of diesel production) creates a multitude of products, including fuels such as diesel and petrol. If diesel engines disappear altogether, there will be little demand for diesel fuel, which will mean an imbalance in the current refinery process. It therefore makes sense to use diesel as a fuel as long as petrol is produced.

Per litre, diesel fuel is more energy dense (its chemical potential energy) than petrol (around 36 MJ/L versus 34 MJ/L) and is a lower fire risk because it has a higher flashpoint than petrol (above 52 °C versus minus-43 °C).

DRIVEABILITY

Because of high in-cylinder pressures during combustion, diesel engines (especially turbodiesels) are known for high torque outputs across the engine-speed range. This results in excellent in-gear performance and enhances driveability. Compared with a petrol unit, a diesel’s limited engine-speed range is less of an issue with today’s proficient automatic transmissions.