Elio Motors recently showed us photos of its three-cylinder engine block prototype the young automaker called a work-in-progress. Now, Elio has sent us a follow-up: Photos of the Elio’s engine head, in prototype form.
An e-mail from Elio Motors showed the engine head looking slightly more complete than the rough-cast engine block we saw during the company’s last powertrain update. The e-mail explained that the Elio’s focus on being fuel efficient — the company claims to be shooting for an 84-MPG EPA highway fuel efficiency rating — means a lot of attention is being paid to the finer details in designing the head, where combustion happens.
Given fuel efficiency is one of Elio’s four “must haves,” there is a concerted effort applied toward combustion attributes, port design and valve events. With each, there is a strong underlying requirement for reliability, which forces attention to geometric tolerances and interactions, metallurgy, metrology, etc. When the engine is downsized, performance remains important such that the airflow characteristics and capability of the cylinder head/valvetrain are critical.
According to the e-mail, the intake and exhaust ports in the head reportedly are designed to provide unimpeded flow into and out of the combustion chamber. Fast burn rates and high knock resistance are enabled by the in-cylinder motion and careful shaping of the combustion chamber, Elio said. The e-mail added that the aforementioned combustion chamber design combined with the engine’s fuel injector targeting allow all the fuel to be aimed toward the back of the intake valve via two steps:
Closed Valve Injection Timing: Allows for better fuel vaporization (heating) in part-throttle light load operationand optimizes combustion efficiency for best fuel economy and lowest emissions.Value Open Injection Timing: This same fuel targeting allows for very effective strategies at high load full-throttle performance. The fuel enters the chamber in atomized state (liquid – small droplet diameter), which cools the combustion chamber and allows for higher compression ratio and more optimized spark timing. In this way, a more cost efficient port fuel injected (PFI) engine can return similar knock resistance to a direct fuel injection (DI) engine.
As one would expect with a sub-1,000 cc engine, Elio said the combustion chamber was designed to be compact, with a low surface-to-volume ratio. The automaker said this minimizes heat transfer out of the combustion chamber — a move that should improve thermal and fuel efficiency. As for the spark plug, Elio said it is angled toward the center of the combustion chamber. That positioning combined with the deep bowl of the piston should help the flame “kernel,” as the e-mail called it — that is, the first kindling of fire that happens when the spark plug ignites the fuel-air mixture in the combustion chamber — to grow at a more efficient rate, helping fuel burn faster. The fast burn rate will help the engine be welcoming of fuel that doesn’t come from the premium pump while maximizing the efficiency of the engine, Elio said.
In-cylinder turbulence is aided by a “squish area” that should help enhance burn rates at the time of ignition, Elio said.
With all this highly efficient fuel-burning going on within the combustion chamber, Elio said the engine also will have excellent homogeneity, or uniformity of fuel-air mixture. Also, the high burn rates reportedly will allow for an aggressive exhaust gas recirculation (EGR) regime that reduces pumping losses under partial load — another efficiency-improving move, according to the automaker. The e-mail said EGR helps reduce combustion chamber temperatures, which reduces oxides of nitrogen (NOx) formation to give the engine a cleaner emissions score.
Finally, Elio said the engine features an upper camshaft cover with built-in cam caps that improve cam bearing performance, reducing the engine’s oiling requirements and allowing for a smaller oil pump with less parasitic loss. The cam cover’s design also allows for reduced parts count during the manufacturing process — which in theory, at least, means less to go wrong with the new engine and a cheaper build cost for Elio. “Decreasing the manufacturing complexity minimizes the cycle time for assembly knowing that time is money,” the e-mail said.
We look forward to hearing more from Elio during the development of its in-house engine. If they pull off not just designing a three-wheel car chassis, but also a whole new three-cylinder engine and make it all work as-promised, we predict a lot of people will sit up and take notice.