DIY Electric Car Forums banner
1 - 3 of 37 Posts

· Registered
277 Posts
so, how does one convert the 300kj needed to push a 1 ton car just over 55mph into watts needed then? by seconds?

how about this?

a natural gas burning 100-150cc generator followed by a stirling engine "turbo generator" to recycle some of the energy lost as heat? any promise of noticeably higher efficiency than a standard ICE there? turbochargers nearly double ICE efficiency. i'd bet a stirling engine is more efficient than a turbo charger if one can be run off the temperature difference between one's hand and ambient air. the heat difference from an exhaust compared to to fresh air is much greater and if propane expands from it's liquid state into a gaseous one for combustion, that could form an air conditioner style "intercooler" for even greater efficiency. i first thought of it in a steam engine configuration until i saw how inefficient steam power is.

my research dead ended with a pure alcohol burnining ICE which would run cheaper than anything if you distilled your own fuel, but natural gas is the emissions champ for easy conversions.

you just can't find much info on hydrogen conversions. virtually any link for it is for a conversion kit of which i've heard rumors many are bogus and a lot of dead links.

there just have to be answers to questions no one has asked yet. i guess this is another dead end though as a puny 5hp stirling running off combustion is HUGE. the returns from an already 5hp engine's exhaust would be minimal, even with it's 40% efficiency.
One Watt of power is equivalent to one Joule of energy expenditure per second. It may require 300 kJ of energy to accelerate a car to 55 mph but that would generally depend on the amount of time taken to do the acceleration. Once you're moving, maintaining a given speed is dependent on your friction and drag losses, and requires a certain rate of energy expenditure - i.e. a certain amount of power.

Turbochargers do improve energy efficiency of an engine but not by 100 percent. They can double the power output but only at a substantially greater fuel consumption compared to the naturally aspirated engine.
As a rule of thumb, a contemporary gasoline engine will typically convert 1/3 of the chemical energy in the fuel to mechanical work at the crankshaft, 1/3 into cooling system heat, and 1/3 into exhaust heat. The turbocharger recovers some of the exhaust heat and effectively turns it into available work at the crankshaft. The end effect is that the exhaust gas temperature of a turbocharged engine is lower than a naturally aspirated engine, for a given gas flow rate. Assuming that equal combustion temperatures are reached, this implies that the turbocharged engine is more efficient.

Stirling engines are interesting in many regards, but their thermodynamic efficiency is determined by the same equation as for any other heat engine, and the hard thing with Stirling engines is to design one that will tolerate very high temperatures at one end and near-room temperature at the other, while also having minimal 'dead' space for the working gas (which ideally is kept at as high a pressure as possible). And you still need a near-frictionless sliding seal for the pistons and a reciprocating-to-rotary motion conversion system. In contrast, the turbocharger can extract the same energy from the exhaust with one moving part.

· Registered
277 Posts
We're not being difficult. Do you read the replies to your posts?

We have posted regarding this several times. I will put it as simple as I can. MASS times VELOCITY equals NOTHING !!!!!!!!!!! Meaning that the product of mass and velocity does not result in any useful quantity in any known system of physics or units in this universe, as far as I am aware.

Furthermore, an erg = 100 nanojoules, which is a unit of energy. ENERGY is not POWER. So you can NOT convert units of energy to units of power.

No simple factor (number) can be used to make a KJ into a watt.

Got that?

Hey Major,
I'm not trying to quibble here but Mass times velocity equals momentum.
p = mv
Take the velocity integral of that and you get the energy required or recovered due to the speed change.
E = 1/2 m(v2^2 - v1^2)

To zeroemission: The above concepts are probably over your head but I didn't intend them for you. I'm sorry that we're not getting the basic idea, that power and energy are not the same, across in a way that you can relate to.

As simply as possible:
Energy divided by time equals power.

It takes a great deal of power to deliver a lot of energy in a short amount of time. A funny car goes from zero to 300 mph in 4 seconds, but it requires about 7000 horsepower to do so.

On the other hand, a tiny solar cell could still deliver megajoules of energy, but it would take years. The solar cell puts out very little power, but the total amount of energy it could deliver is nearly unlimited if you don't care how long it takes.

· Registered
277 Posts
my entire purpose in asking questions is to read replies, but not when they take on a condescending tone. i just cannot get along with that personality type at all.

too bad i don't know either the Cd or rolling resistance of my design. i will take a look at it and see if it's possible to ignore those 2 varables and get results.

rough draft of my "cheap, light & efficient" design

if serial hybrids didn't guzzle pretty much the same amount of gas as a standard ICE car, it would be possible to turn a design like that into an under 500 pound vehicle with a very low Cd profile.

i'm not looking for Nth degree accuracy, just a ballpark estimate to design around. the best i've been able to do is imagine a space in between motorcycle conversions and typical EV conversions, moreso motorcyles as my nylon skinned tube chassis concept is closer to them in weight and drag coefficient.

if one can get better performance than a typical EV conversion building from scratch, but for the same price or less, unless you're given a donor car, it makes more sense to build an "electric skateboard" from scratch to me. i'm not a fan of imitating the look of ICE either unless one gets EV vanity plates to advertise the fact.
If you want to get range with your design then figure out a way to put fenders on it (open wheels are very bad for air resistance), and find some narrow, smoother tires. Big knobbies are very bad for rolling resistance.

As a ballpark: Open wheels and square profile front and back, which you have, will probably give you a drag coefficient in the range of 0.7.
For rolling resistance you'll just have to do some Googling and put in numbers that are in a reasonable range.

For the frontal area, you should include everything between the pavement and the highest part of the car.
1 - 3 of 37 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.