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Comment by 01100011 | Hacker News Reader

Would a 14% increase in thermal efficiency translate into a meaningful reduction in carbon emitted per mile driven? This is interesting technology, but I'm not sure it will prolong the internal combustion engine, at least as far as mass market consumer transportation is concerned.

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> Would a 14% increase in thermal efficiency translate into a meaningful reduction in carbon emitted per mile driven?

Yes (as long as the engineers don't seriously mess up).

Nearly all of the energy released by burning gasoline is in the form of heat. ICE engines use that heat to expand gases, and capture the expansion as mechanical motion. Modern automotive ICE engines capture roughly 40% of their combustion output as mechanical work. The remaining 60% of the energy, still in the form of heat, is lost through the radiator and the tailpipe. Improving that ratio allows you to burn less fuel to get the same work done. Carbon is emitted by burning fuel, so burning 14% less fuel (yet accomplishing the same work) would result in approximately 14% less carbon being released for the same task.

Off the top of my head, here are some reasons that improving theoretical thermodynamic efficiency might not reduce carbon emissions:

* The extra parts to increase the efficiency (the fourth piston) could sap more energy in friction than they capture from the waste heat. (This would cause the engine to not actually have the claimed thermodynamic efficiency -- it's back to producing the same amount of waste heat as before, just in a more complicated way.)

* The combustion could be hard to control and inefficient, sending unburned fuel out the exhaust pipe. (This lowers the combustion efficiency, but doesn't actually change the thermodynamic efficiency -- it's still producing less heat per gram of burned fuel.)

* The higher compression ratio, and the different mixing pattern caused by the sliding valve, might cause more-potent greenhouse gases to be produced than CO2. (This doesn't change the efficiency at all, but it does affect the environmental impact similarly to burning more fuel in a less-efficient engine.)

I'm thinking this might have interesting applications as a range extender of EVs, like e.g. available for the BMW i30. A vehicle with 150-200km electric range and an optional extender could be quite compelling for lots of usecases.

It looks like this would make for a pretty heavy engine, with four cylinders to do the work of 1-2 in a more traditional engine. So it might not be worth the trouble in a car, but may be useful in stationary or marine applications.

Yes, hybrids are definitely a viable use-case. There are also other applications where a combustion engine makes much more sense, especially if this design can be used for smaller engines like chainsaw engines and lawnmower engines.

The article doesn't mention what kind of fuel this new engine uses, but if it can run on ethanol, or synthesized hydrocarbons like E-diesel then this could definitely be a good thing.

Chainsaws and lawnmowers do need to go electric now.

They are the ones that ought to go electric first. The easier ones.

Thankfully electricity is not available everywhere, e.g. in the middle of a forest.

> Thankfully electricity is not available everywhere, e.g. in the middle of a forest.

Well, do you easily find a refueling station in the middle of the forest? If you brought spare fuel containers, why wouldn't you bring all-the-same spare batteries?

Energy density is probably quite important for something handheld like a chainsaw. I doubt batteries are able to replace that except for some light garden use.

This. A 5l can of fuel is easier to drag along and I suspect current battery tech won't be good enough for professional use.

I have a chainsaw that runs on mains power. It's really nice (and quiet) for smaller tasks close to the house, but it doesn't help once you get outside extension cord-range.

40 volt electric chainsaws are fine for anything under 6 inches in diameter. That covers almost all household use cases as well as many trail thinning situations.

Yeah, the current offerings just won't cut it for professional use though, which I suspect account for much of chainsaw emissions.

They are getting there, at least for lawnmowers. Robot movers are getting close in price to traditional mowers. There are a good selection of chainsaws for gardening and light usage that are electric.

But if you, like me, use 2-3l of bio-fuel a year during only 2-3 days on the chainsaw there are not many options and not much to save. Even added up all the fuel used on chainsaws is microscopic compared to for instance savings going from giant trucks to smaller trucks or cars, which is an easy fix by changing regulations in US to not favor giant trucks and subsiding fuel

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