San Antonio man has engine that gets 100 mpg | Hacker News Reader

San Antonio man has engine that gets 100 mpg

khou.com

63 pointscoreyp_148 comments

This recycling feature boosts the engine's efficiency to a whopping 50 percent. For comparison, a standard internal combustion engine operates only at 14 percent efficiency.

I don't know what a "standard internal combustion engine" is, but 14% is absurdly low. Maybe a Ford Model T would be around there? A glance at

https://en.wikipedia.org/wiki/Specific_fuel_consumption_(sha...

shows efficiencies of ~30% for typical gasoline engines of the automotive type (which agrees with what I remember when I studied this stuff), and closer to 50% for large two-stroke diesels.

The most efficient fossil fuel-based engines are massive two-stroke diesels found on extremely large ships and in some peaker power gensets which currently have efficiencies just over 51% and BSFC's over 275.

https://en.wikipedia.org/wiki/Brake_specific_fuel_consumptio...

In this case, he may have matched the performance of very large engines, which have the advantages of optimizing for scale, but time will tell whether this solution can deliver.

> The most efficient fossil fuel-based engines are massive two-stroke diesels

Unless you count combined-cycle gas turbines (also found on big ships and powerplants), which can squeeze above 60% efficiency.

> "Josh “Mac” MacDowell says he not only has the engine, he has come up with an idea, strong enough the U.S. patent office has given him a patent for it."

Gave me a chuckle.

A worthy submission to the "Found Prose" subsection of the Little Lytton Contest...

As usual, Tom Murphy has a great top-down analysis of why cars don't get 100 mpg:

http://physics.ucsd.edu/do-the-math/2011/07/100-mpg-on-gasol...

Spoiler alert: it's mainly because cars are shaped like cars, not fish.

Don't forget those humble brakes and corner turning.

Oh very insightful. That means that there important potential efficiency gains if we can take advantage of drafting (like ducks flocks) based on automated driving.

https://en.wikipedia.org/wiki/Volkswagen_1-litre_car

aerodynamics on a car taken to the extreme, to the extent that it has cameras and LCDs instead of side/rear view mirrors.

It should be possible in terms of energy expended.

This guy : http://diesel-bike.com/Centurion/urba_centurion.html built a kit car from these plans : http://www.rqriley.com/cent.html and got a tested and verified 200mpg after tuning (scroll down the circa-GeoCities page to see the results from his participation in the Toyota Green Prix).

Not sure the car above would be good as a daily driver, however.

What happened to Dean Kamen's Sterling engine?

Here's one link from 2013- http://www.greentechmedia.com/articles/read/nrg-energy-deplo...

Uh, wat. Honda engines are insanely efficient. I doubt this guy knows anything that Honda/Toyota doesn't.

Honda could easily give you a 100mpg car, if it weren't for those meddling kids at the NHTSA. Damn them and their stupid, heavy airbags|crumple zones|roll cages.

Removal of that weight would not be enough to hit 100mpg, as evidenced by the fact that steady state cruising does not get you 100mpg

I'll "take effects of rolling resistance" for 200, Alex

I forgot that this was Hacker News, where "Serial Entrepreneurs" moonlight as leading experts in automotive engineering.

Right, so you're an expert in automotive engineering then?

Expert? No. But I did work with many industry experts while at Honda. I've heard plenty on the topic of engines/mpg.

Thanks for playing!

Oh, so you're not an expert at all by your own admission, but you won't listen to anybody else who is also not an expert.

I'm so sorry to inform you of this but, you actually lost the debate here.

Weak straw man. You're terrible at making arguments.

Shoo.

Replying to every little rebuttal that I make only makes you look worst.

Shoo yourself.

Find a wrecked Prius and a CRX and build your own.

Alright, someone who knows more about this topic tell me the catch to this.

Without knowing the test conditions, torque and other performance results, the lone number of fuel milage is worthless. Stirling engines are usually big, heavy suckers, better for fixed installation than vehicles.

Not to mention with all the mpg test fraud going around these days.

meh, totally false. There have been prototype cars before that use stirling engines, the main flaw has been slow start times and poor speed change (it takes a while to heat up, and for changes in heat to take effect). Making it a hybrid solves both of those problems!

Presumably the big different is that 200 years ago you did not have decent batteries and electric motors.

I'm really surprised by how little attention this key fact is getting. The best engine for a range extender duty is very different from the best engine for direct drive, internal combustion or not.

but is it worth the extra weight and complexity of a second engine and fuel source?

The answer at present appears to be "yes, unless your use case allows frequent recharging" (such as an EV commuter car/grocery getter, alternate transportation available for long trips, no likely situation where unplanned long trip would be necessary) or there's large financial incentives to ditch the engine (i.e. taxpayers paying people for the inconvenience).

Probably the (non-CO2) emissions. Most engines on the market have to optimize both for fuel efficiency and minimization of pollutants. As you might remember from the VW scandal, you can improve fuel efficiency at the cost of greater NOx emissions.

Also, they need to be big and strong enough to pass crash tests, which further reduces fuel efficiency. I don't think this car would pass those either.

Since no article has mad it clear, what is providing the heat source here for the Stirling engine? Is he pumping the heat from a standard gasoline engine to the stirling engine, is that the idea?

That was a lovely bed-time story. Unfortunately, that's all it was.

Can you please explain why?

They probably mean that it's like the stories about 100x battery capacity improvements that end up as a 20% capacity boost in actual products that appear on store shelves. Prototypes are always more impressive than marketable products.

In his case, maybe there are acceleration/deceleration issues, maybe the engine would be cost prohibitive for manufacture, or maybe he'll have to modify the vehicle itself to achieve the 100mpg number. The point is that there's likely to be some constraint that makes it impractical.

As an extreme example: https://en.wikipedia.org/wiki/Pac-car_II

There's a reason that we aren't driving hydrogen fuel cell cars with 12,600 MPGe fuel economy.

He made a hybrid with a Stirling engine, hence the 200-year-old technology part of the clickbaity headline. It looks fascinating. Unfortunately, the article is almost completely number and depth free.

Yes, that's because Fox News.

...at which point, you might ask yourself "Fox News? On MY HN?!"

Note to others- he wrote that because the original link on this post was foxnews, but the new link is more well-written and from KHOU, a CBS affiliate.

He didn't make anything. Which is why the article is depth free. It's all speculation about what he plans to do in the future.

The source article is much better: http://www.khou.com/features/san-antonino-man-has-engine-tha...

The DigitalTrends rewrite omits a lot of details and doesn't add anything.

Attention dang: an appropriate replacement?

Sure, we changed to that from http://www.foxnews.com/leisure/2016/06/15/man-builds-100mpg-.... It has an annoying autoplay video, but if the article is better that's enough.

An engine doesn't get 100 mpg, a vehicle does.

Attach it to a normal-sized vehicle and get 100 mpg under realistic driving conditions, and I'll be impressed. ('til then I'll be internet-snarky!)

The fifth paragraph addresses the significance of your point.

I'm skeptical, but I applaud him for making public a very specific and short-term goal that we can all watch: coast-to-coast USA on 40 gallons of fuel in a small SUV.

>> coast-to-coast USA on 40 gallons of fuel in a small SUV

Without having a source, I suspect a caveat wherein he will plug in to fully recharge the electric battery every X hours, which would be far less impressive.

Now, if this is cross-country, on a single 40 gallon tank, without plugging in to recharge, in an SUV that is not gutted to reduce the vehicle's weight... that would be impressive.

Doing it with plugging in would be a bit pointless. You could do that with no fuel or engine.

> > Without having a source, I suspect a caveat wherein he will plug in to fully recharge the electric battery every X hours, which would be far less impressive.

FTA, FWIW: "McDowell is using a Stirling engine, coupled with thermopile technology to make it possible to drive a Hybrid electric car and never have to stop to charge it."

Ah, thanks for that. I read the article fully, but apparently missed or forgot about that line in the first paragraph.

My intuition was that the Stirling engine would partially recharge the battery while it runs. If it can truly keep the battery fully charged, that is quite awesome. Time will tell. :)

This needs to be higher up. Likewise, a thermal cycle (Otto, Stirling etc.) doesn't get X% efficiency, an engine (running at a given hot/cold temperature with pumping losses etc) does.

Article says "The Stirling engine is capable of using roughly 50% of the energy it produces. An internal combustion engine, like the ones in our vehicles, uses about 14%." This isn't even wrong - the efficiency of both of these engines depends on a huge range of factors.

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