New diesel engine that runs on petrol announced

Posted on July 17th, 2018 by Rob Marshall

New diesel engine that runs on petrol announced

With the considerable anti-diesel rhetoric that exists currently, one would think that the world had turned its back on compression-ignition engine technology. That is untrue. While new UK sales have declined, demand for used diesel cars has risen. One of the major issues is that there is no realistic alternative to heavy-oil cars, on the used car scene particularly.

It appears that Mazda agrees, with the carmaker stating:

“Electric powertrains do not, in fact, currently satisfy society’s wish for a drastic reduction in greenhouse gas emissions.”

Mazda cites that two-thirds of global electricity production relies on the use of fossil fuels, which is why the Japanese manufacturer believes that regulations, which place the emissions of an EV (Electric Vehicle) at zero, are disingenuous. This is because, it claims, when converted to a ‘Well-to-Wheel’ figure, the average CO2 emissions of an EV can be very close to that of a conventional fossil-fuelled car, dependent on the energy mix that creates the electricity.

It is a reasonable argument. Yet, it must also be contemplated that the CO2 implications of fuel production is not considered in the assessment of both petrol and diesel vehicles’ emissions. This was the view, taken by Britain’s ASA, when ruling in favour of Renault UK’s advertising claim that an electric car model has zero emissions.


New tech looking at older tech

In any case, Mazda’s 2.0-litre SKYACTIV-X SPCCI engine is a technical oddity but it is an interesting one. As the main petrol/air ratio employed is so lean, its spark plugs are unable to ignite the mixture. Therefore, the manufacturer has chosen to raise the compression ratio to 16:1 (very close to modern direct-injection diesel engine figures) but the fuel is not ignited by the compression, unlike a conventional diesel. Optimised fuel injectors are fired several times during each cycle. This provides not only a pre-combustion facility, during which time a relatively rich mixture is directed towards the spark plug tip, where the initial burn is instigated, but also post-combustion injections provide the required power and economy characteristics. However, very cold start and full-power conditions, will see the engine adopt, what Mazda calls, ‘conventional combustion’, meaning that the 35-40% fuel reduction (compared to the company’s MZR engine of a decade ago) might be negated completely, if the car were driven hard, especially when cold.


Nonetheless, it will be interesting to establish whether, or not, this engine offers substantial real-world improvements in both fuel consumption and exhaust emissions, most notably of NOx, which have been a problem to suppress in Japanese lean-burn engines of the past. Mazda plans to introduce the unit to the British market from next year.