[OT] Engine braking

Adam Wilson flyboynw at gmail.com
Thu Aug 1 13:53:55 PDT 2013


On Thu, 01 Aug 2013 13:17:51 -0700, Walter Bright  
<newshound2 at digitalmars.com> wrote:

> On 8/1/2013 12:39 PM, Andrei Alexandrescu wrote:
>> You betcha. Related, you destroyed the myth that engine braking is any  
>> bad, but
>> I bet money nobody changed opinions.
>
> For an engine designed for it, sure. For an engine not designed for it,  
> no. A carbureted engine is still going to have the unburned gas problem  
> (and you're not going to be very green pumping out semi-burned  
> hydrocarbons out the tailpipe). I don't know at what point injected  
> systems began shutting off the fuel when backdriving.
>

I think most manufacturers made that change in the early 80's with all the  
EPA mandates. So basically anything still on the road that isn't a  
Classic. :-)

>> Also, there is a beauty about electrical engines - their theoretical  
>> efficiency
>> is 100%, they are simple, principled, entropy-neutral, and work on  
>> conservative
>> laws. (Batteries are more unwieldy though.)
>
> You're right, it's all about the batteries. They're a gigantic problem  
> that, while there are incremental improvements, is still far from a  
> solution. But gasoline engines are also getting incremental  
> improvements. Modern ones are way, way better than the ones from the  
> 60's in just about every aspect.
>

And getting better every year. We're starting to see widespread use of  
Gasoline Direct Injection and better ignition technologies. The reason we  
aren't seeing major improvement in gas mileage is because every year new  
government safety mandates add an average of 30lbs to the car.

> There's an inherent efficiency in gas cars in that the energy is  
> generated on site. For electric cars, the energy is generated elsewhere  
> (at the power plant), and then you're faced with all the losses from  
> transmitting the energy, storing it, and recovering it. It's a tough  
> hill to climb. Gasoline is pretty remarkable in its energy density and  
> portability.
>

In fact, in raw terms, Gasoline has significantly higher energy density  
than batteries. And that matters more than you'd think. The Prius for  
example weighs something like 2900lbs where the typical gasoline powered  
car of the same size weighs around 2000lbs. This is due to the need for a  
large array of batteries and carrying around both a gasoline motor and  
electrical motors. That has a direct effect on the amount of energy  
required to move it's mass. So per pound, Gasoline has Batteries  
thoroughly beaten, and according to a friend of mine who works in the  
field (he designs the inverters that convert battery energy to energy  
usable by things like automotive electric motors) this will remain so for  
the foreseeable future. (AKA, nothing groundbreaking on the horizon.)

> BTW, with a manual trans, you can get quite a bit better mileage than  
> the EPA ratings. Google "hypermiling" for ways. I do that stuff  
> routinely.
>

You did forget to mention that you piss off everyone behind though... ;-P

-- 
Adam Wilson
IRC: LightBender
Project Coordinator
The Horizon Project
http://www.thehorizonproject.org/


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