Of the thousands of components that come together to make a vehicle operational, the engine is often viewed as the most important. Fittingly, it also tends to generate the most questions. In case you missed it, last week’s Momentum presented answers to engineering questions we received from Elio Motors supporters. Last week focused on more general engineering questions, while today’s Momentum will answer engine specific answers.
Q: Are the valves hydraulic or will they need to be adjusted? If so, what mileage interval?
The Elio engine valves are direct acting buckets that will not require adjustment at any mileage interval. This design is currently used on popular engines. Find below a CAD rendering of the current valvetrain:
Q: How does 11:1 compression run on 87 octane gasoline?
This question is quite common, and the answer is multifaceted. A compression ratio of 11 is being used for the production engine. The higher geometric compression ratio allows longer expansion ratio, which is a primary factor in fuel conversion efficiency. IAV has designed the engine to avoid knock primarily by reduced cylinder pressure via reduced volumetric efficiency via intake valve timing. The secondary knock avoidance mechanism is spark retard. The key enabler to the high compression ratio is enhanced cooling which controls combustion chamber metal temperature.
There are several main factors that allow us to achieve our targeted mileage with an 11:1 compression ratio:
Enhanced intake and exhaust port flow
Enhanced combustion through swirl/tumble optimization
Sequential port fuel injection (reduce event-to-event variability)
Advanced spray targeting provides gasoline direct injection-like (GDI) cooling benefits without the cost
Improved cooling reduces octane requirements enabling higher compression ratios
Variable valve lift allows optimal engine residency for fuel economy
EGR with cooler
Piston and Head Shape: The design on the Elio piston and head allows for maximization of the stroke.
Valve angle: The angle of the valves when incorporated with the changes above, allow for a super-efficient engine.
This compression ration aligns with current and future compression ratios of vehicles. If you look at the current and near future designs they range anywhere from 10:1 to 16:1 ratios.
Q: Will the Elio use a timing chain or a timing belt?
The Elio engine will use a timing belt. We have decided to use a timing belt for several reasons. First, a timing belt reduces weight, friction, and vibration. Second, a timing belt fits the simplicity of the design. Finally, a timing belt will enhance the longevity of the engine. Using a timing belt meets our objectives and is preferable to the customer.
Q: Will the Elio have an interference or non-interference engine?
The Elio will have a non-interference engine. In a non-interference engine, the piston cannot move into the valve area.
Q: Will a different engine, with a different power source, ever be available?
While a different engine may be possible in the future, our first model will run solely on unleaded gasoline. The primary reason we are using gasoline is to keep our base price as low as possible. Our sole focus is getting the vehicle to market as quickly as possible and at an unbeatable value proposition. That said, we also believe that the vehicle platform is perfect, in the future, for alternative power sources.
Again, thank you to all of our supporters that provided us with these tremendous questions. As we continue down the path toward production, we will endeavor to provide you a look into the process of designing and engineering an innovative new vehicle.