As the axe prepares to fall on Toyota’s petrol V8s, could a new diesel family take their place?
A patent application released in the US points to a potential new engine development by Toyota, leading to a raft of speculation from American publications.
The application, uncovered TheFastLaneTruck.com, was initially filed in December 2019.
However, with reports Toyota will drop its V8 range, which powers a selection of SUVs and pick-ups in the US, the timing points to an engine that might fit those applications.
The patent itself concerns “a compressed self-ignition type internal combustion engine” which points to a diesel engine, where traditionally, compression ignition is used to ignite the fuel-air mixture, unlike petrol engines which usually rely on spark ignition.
Initial reports highlight the engine’s high-compression nature, though seem to pay little heed to the fact most diesels run a high compression ratio to allow the self combustion of fuel in the absence of an ignition source.
More note-worthy are the illustrative diagrams and accompanying description which suggest a multi-path injection system could be at the core of the new engine, using advanced injection control to minimise smoke and emissions in turn.
The diagrams show an injector that would sit within an enclosure used to direct fuel, with different path lengths and spray control to more finely adjust the ignition characteristics of the combustion cycle.
Pre-heating of the fuel before it reaches the glow plug may occur. “Both the suppression of smoke and improvement of ignitability may be achieved” according to the filing. It’s a statement repeated numerous times, with the various injection paths creating high-ignitability and low-ignitability fuel paths, the combination of which appear to reduce smoke and improve the fuel’s ignitability.
By altering the fuel spray path and pre-mixing fuel spray and intake air the new engine aims to cut down on self-ignition of fuel, which can occur in diesel engines, creating an unstable burn where fuel ignites ahead of its ideal timing in the compression cycle.
With better ignition control thermal efficiency should be enhanced.
Not only that, but the suppression of smoke points to an engine that may be able to improve on emissions performance to a point where current control measures like diesel particulate filters or exhaust additives, like AdBlue, are not required.
From the application it’s unclear if ‘smoke’ specifically points to particulate matter, nitrogen oxides, or other exhaust gases.
Although glow plugs are specifically mentioned in the release the fuel type isn’t mentioned. While diesel seems the likely candidate there’s also a chance the patent may apply to a compression-ignition petrol engine not unlike Mazda’s recently released Skyactiv-X spark controlled compression ignition engine.
Other modifications point to the removal of a traditional glow plug, instead equipping the injector outlet (or at least one of) with a heated surface to adjust fuel temperature to the required temperature the moment it reaches the combustion chamber.
How this plays into Toyota’s future products plans remains to be seen, and as with any patent application may simply be Toyota’s way of protecting intellectual property rather than a guarantee of production.
The patent itself applies only to a single combustion chamber or cylinder and, short of expressly detailing two intake and two exhaust valves, doesn't mention cylinder count of a potential future engine, though in reality would be applicable to four, six or eight cylinder engines as required,
It’s unclear how TFLTruck arrived at the conclusion the application specifically applied to pick-up trucks. While the American market leans towards petrol engines in some of its largest utes and SUVs, nearly every medium and full-size pick-up has the option of a diesel engine.
With diesel passenger cars all but wiped from the American market the leap to a diesel-powered engine to step in for the departing petrol V8 range isn’t entirely out of the question. All the more so if Toyota can manage to overcome some of the issues surrounding diesel emissions performance.
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