Comment by londons_explore
18 hours ago
Worth noting the design of the internal combustion engine hasn't changed much in 50 years.
The thing that has changed is the control systems.
What used to be a primitive mechanical way of mixing fuel and air (the carburettor), is now an electronic fuel injection system, with the fuel air ratio very carefully matched to reduce pollution (fun fact: modern cars release so little carbon monoxide, you won't kill yourself by starting one in a garage (but don't try it just incase your car is faulty)). Catalytic converters use any tiny fuel air imbalance to reduce carbon monoxide and soot, and on the other side nitrous oxides, by slightly increasing and decreasing fuel air ratios.
There's also been advancements in cylinder head technology (i.e., VTEC, VVT, etc), which I guess also falls under control systems, but worth mentioning as these technologies are very cool. Honda's iVTEC has it down to a damn science with how to optimize valve lift & duration across the entire RPM spectrum.
The orbital family of ICE engine of 1972 has seen a lot of ongoing innovation and crossover variations with other rotary engines (like the Wankel) in past decades - such engine variants have had a major place in UAV (and other) drones.
* https://en.wikipedia.org/wiki/Sarich_orbital_engine
* https://www.orbitaluav.com/
* https://www.aieuk.com/225acs-wankel-rotary-engine/
> fun fact: modern cars release so little carbon monoxide, you won't kill yourself by starting one in a garage
Modern cars still release as much CO2 as older cars… which is still incompatible with human respiration.
Another fun fact: the body's suffocation response isn't caused by lack of oxygen. It's caused by high CO2 levels in the blood [0]. If your car floods the air with CO2, you will respond like someone is holding your head under water.
Carbon monoxide kills you by binding more strongly to the hemoglobin than the O2. You don't notice, because the CO2 removal mechanism continues to work fine. You'll usually die before realising anything is wrong.
What I am surprised by is that cams are still used to operate the valves.
Given to how precise these need to be these days, I would've guessed they would've switched to electronically actuated valves.
It’s because of the good enough precision at low cost that we use cams, it’s extremely difficult to get precise movement and the forces and speeds required when an engine is operating at >5000 rpm. It’s not impossible but the trade offs are rarely worth.
The exact valve timing isn’t really a big factor in emissions as much as temperature control and exact AFR control. I mean valves need precise timing to avoid coming into contact with pistons but if you’re already at that level of precision then you gaining more precision won’t really reduce your emissions.
Of course being able to change the timing of your valves helps with both efficiency and emissions, but VVT does that pretty well.
Fiat (and other's I'm sure) have the [MultiAir system](https://www.caranddriver.com/features/a16580674/fiats-multia...) which doesn't use cams to actuate valves
And here's an example of someone that retrofitted a Miata to use a similar [air-actuated valve system](https://youtu.be/E9KJ_f7REGw)
The very first image at the very top of the MultiAir article shows, prominently, a camshaft and the cams used to actuate the valves.
I was going to point to Koenigsegg’s Freevalve system and, in the process of looking for a link, learned that it was cancelled.
> What I am surprised by is that cams are still used to operate the valves.
Kinda, it's all continuous variable valve lift now:
https://en.wikipedia.org/wiki/Variable_valve_lift
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And there are also other parts for reducing the pollution like DPF, EGR and Adblue systems.
Unfortunately they also reduce the reliability.