A simple gadget to increase MPG 20%!

Originally posted by twhitehead
Lets say an engine currently burns x percent of its fuel in in order to produce y amount of heat of which only 50% actually drives the wheels.
Then a 20% increase in x should result in a 20% increase in y, and a 20% increase in power at the wheels. So it looks like I was wrong, and we don't need to burn more than 20% more fuel.
But I still think that t ...[text shortened]... % of their fuel, so the device remains somewhat suspect unless there is something I am missing.

I am agnostic on this device but I am thinking the full results would require analyzing the combustion products also, before and after install of the device. That would tell if the combustion efficiency goes up or not. It would stand to reason to expect a cleaner burn as well as increase in combustion efficiency.

Originally posted by twhitehead
I have no objections to your claim that the maximum efficiency of converting the heat to power is a mere 64%
However as Ponderable has already pointed out, that is almost irrelevant to the situation or possibly argues in favor of ponderables initial claim. Separate the engine into two parts, one part (1.) that converts chemical energy into heat and anoth ...[text shortened]... (more like 30-40% ).
This means that current engines must be burning only 60-70% of their fuel.

There is a significant amount of chemical energy left in the fuel products after combustion. If Ponderable meant that some of the fuel doesn't get burned, he should have said so.

Also, percentage increase in mileage is based the existing mileage, not the theoretical maximum. If the car runs somewhere around 35% efficiency right now, a 20% increase only increases the total efficiency by 20% * 35% = 7%.

Originally posted by PBE6
There is a significant amount of chemical energy left in the fuel products after combustion. If Ponderable meant that some of the fuel doesn't get burned, he should have said so.

Would you know roughly how much. I am interested.

Also, percentage increase in mileage is based the existing mileage, not the theoretical maximum. If the car runs somewhere around 35% efficiency right now, a 20% increase only increases the total efficiency by 20% * 35% = 7%.
I do realize that. However, if the efficiency gain is obtained entirely by increasing the percentage of fuel burned, then does that not mean that 20% more fuel must be burned? Or am I missing something?

Originally posted by twhitehead
Would you know roughly how much. I am interested.

[b]Also, percentage increase in mileage is based the existing mileage, not the theoretical maximum. If the car runs somewhere around 35% efficiency right now, a 20% increase only increases the total efficiency by 20% * 35% = 7%.
I do realize that. However, if the efficiency gain is obtained entire ...[text shortened]... el burned, then does that not mean that 20% more fuel must be burned? Or am I missing something?[/b]

The article says that the smaller droplets lead to "more efficient and cleaner combustion than a standard fuel injector", so I don't think it necessarily must increase the amount of fuel burned.

The properties of the fuel will change subtly with changes in droplet size. If we assume the droplets are spherical, then the surface area (SA) of each droplet is 4pi*r^2 and the volume (V) is (4/3)pi*r^3. Taking the ratio of surface area to volume, we find that SA/V = 3/r. Therefore, as the droplets get smaller the SA/V ratio goes up. This is important because it will increase mass transport across the droplet boundary, making the reaction faster. Also, the smaller size will allow heat to better permeate the entire droplet, maintaining a higher temperature throughout the droplet as it burns. When fuel is burned at a higher temperature, the complete combustion reaction (forming CO2 instead of CO) is more favoured, resulting in cleaner burning fuel. It's my guess that these factors is where the increase in efficiency and the decrease in soot/CO lie.

It may also be the case that a greater portion of the fuel gets burned, but I would imagine that most if not all already gets burned in the engine, otherwise there'd be a significant amount of fuel leaking out of the tailpipe. I think it's more akin to burning woodchips vs. a fire log (both get burned all the way through, but the process is faster and cleaner with the smaller woodchips).

Originally posted by PBE6
The article says that the smaller droplets lead to "more efficient and cleaner combustion than a standard fuel injector", so I don't think it necessarily must increase the amount of fuel burned.

The properties of the fuel will change subtly with changes in droplet size. If we assume the droplets are spherical, then the surface area (SA) of each droplet is ...[text shortened]... ed all the way through, but the process is faster and cleaner with the smaller woodchips).

That would be especially true in the case of diesel engines, which are known for their carbon dust emmisions, soot, in other words. No matter how clean the burn there will be some soot left over, and soot is just an unburned fuel so if you burn what you have more efficiently, there will obviously be less soot left over.

Originally posted by sonhouse
That would be especially true in the case of diesel engines, which are known for their carbon dust emmisions, soot, in other words. No matter how clean the burn there will be some soot left over, and soot is just an unburned fuel so if you burn what you have more efficiently, there will obviously be less soot left over.

The question is whether there is currently 20% of the fuel left unburnt. Having seen what a diesel in poor shape (but still running) can produce in terms of clouds of tailpipe exhaust, I tend to think that in most diesel engines over 95% of the fuel gets burned.

Originally posted by PBE6
It may also be the case that a greater portion of the fuel gets burned, but I would imagine that most if not all already gets burned in the engine, otherwise there'd be a significant amount of fuel leaking out of the tailpipe. I think it's more akin to burning woodchips vs. a fire log (both get burned all the way through, but the process is faster and cleaner with the smaller woodchips).

I understand your explanation about how the fuel burns hotter and faster, but I am still missing the point as to how that helps. Surely the total amount of energy from the fuel is converted to heat however fast it burns, or is it a case of the heat being lost out the exhaust valves?

I am not saying you are wrong about anything, I just want to understand it better.

Originally posted by sonhouse
That would be especially true in the case of diesel engines, which are known for their carbon dust emmisions, soot, in other words. No matter how clean the burn there will be some soot left over, and soot is just an unburned fuel so if you burn what you have more efficiently, there will obviously be less soot left over.

Perhaps there is some confusion over what the term "unburned fuel" means. I was using this term to describe diesel fuel that enters the combustion chamber and also leaves as diesel fuel. I think others are using this term to describe diesel fuel that enter the combustion chamber and leaves as some sort of intermediate and not as products of complete combustion (CO2 and water).

According to this Wikipedia article, soot is an intermediate in the combustion process, so although it has burned it hasn't burned "all the way":

http://en.wikipedia.org/wiki/Soot#Description

Originally posted by twhitehead
The question is whether there is currently 20% of the fuel left unburnt. Having seen what a diesel in poor shape (but still running) can produce in terms of clouds of tailpipe exhaust, I tend to think that in most diesel engines over 95% of the fuel gets burned.

According to this Wikipedia article, you're probably right about a poor engine not burning a significant portion of the fuel completely:

http://en.wikipedia.org/wiki/Diesel_engine#How_diesel_engines_work

Originally posted by twhitehead
I understand your explanation about how the fuel burns hotter and faster, but I am still missing the point as to how that helps. Surely the total amount of energy from the fuel is converted to heat however fast it burns, or is it a case of the heat being lost out the exhaust valves?

I am not saying you are wrong about anything, I just want to understand it better.

http://en.wikipedia.org/wiki/Diesel_engine#How_diesel_engines_work

According to the above article, the diesel engine works by compressing the fuel adiabatically to 15-20 times normal pressure, thereby increasing the temperature of the fuel to ignition temperature. Also, as the fuel droplets vaporize from their surface, the vapours ignite and the droplet burns from the outside in. Both of these processes are mass transport phenomena where the rate of change of the droplet volume |dV/dt| increases with time, much the same way that peeling successive equally thick layers of an onion decreases the volume of the onion faster the closer you get to the middle.

The total amount of energy released from this combustion reaction would be the same no matter what rate it took place at (provided the reactions were the same), making the energy released a state function. However the amount of work done vs. the amount of heat generated is path dependent. One example of this is given in the same article:

http://en.wikipedia.org/wiki/Diesel_engine#Cold_weather

During cold weather starts, the amount of heat absorbed by the cold engine block decreases the amount of work done on the piston. In a normal engine, having a quicker explosion of fuel allows more of the work generated to be directed at the piston, and less heat being dissipated as random motion in the fuel and surrounding engine.

Originally posted by PBE6
According to this Wikipedia article, you're probably right about a poor engine not burning a significant portion of the fuel completely:

http://en.wikipedia.org/wiki/Diesel_engine#How_diesel_engines_work

I still cant find any reference to how much chemical energy is typically converted to heat in well running diesel engine. The Wikipedia article implies that most, if not all is burnt.

What I did come across was

http://en.wikipedia.org/wiki/Six_stroke_engine

which claims that by harvesting some of the excess heat produced in the engine, a gain of 40% efficiency has been achieved.

This all makes me think that current engines are highly inefficient.

If we create a six stroke, hybrid with the device from this thread we could easily double our fuel efficiency! A perpetual motion machine is almost in sight!

Originally posted by twhitehead
I still cant find any reference to how much chemical energy is typically converted to heat in well running diesel engine. The Wikipedia article implies that most, if not all is burnt.

What I did come across was

http://en.wikipedia.org/wiki/Six_stroke_engine

which claims that by harvesting some of the excess heat produced in the engine, a gain of ...[text shortened]... hread we could easily double our fuel efficiency! A perpetual motion machine is almost in sight!

This is interesting, never heard of a 6 stroke engine before. I wonder what this electrification gadget would do to the economy of such an engine?

Originally posted by sonhouse
This is interesting, never heard of a 6 stroke engine before. I wonder what this electrification gadget would do to the economy of such an engine?

Damn, I was about to mention the 6-stroke and TWhitehead beat me to it.

Seems there are lots of different versions but the one I know about injects a water spray into the cylinder at the end of the exhaust stroke. The water vapourises, causing a powerful 'steam' stroke and is then expelled with a final exhaust stroke.

The benefists are obviously an extra power stroke for the same fuel and the negation of any need for extra cooling since the steam stroke does the cooling for you.

The drawbacks are potential corrosion within the cylinder, the need to carry a water tank and possibly the need for a stronger block as you are turning your engine into a boiler.

But I think it sounds superb.

--- Penguin

Originally posted by Penguin
The drawbacks are potential corrosion within the cylinder, the need to carry a water tank and possibly the need for a stronger block as you are turning your engine into a boiler.

I doubt whether a stronger block is required as the steam stroke takes place inside the cylinder and probably does not produce more power than the typical power stroke.

Regarding the corrosion issue, normal fuel combustion produces water as a by-product, so I am not sure whether it would significantly change that.

Originally posted by twhitehead
I doubt whether a stronger block is required as the steam stroke takes place inside the cylinder and probably does not produce more power than the typical power stroke.

Regarding the corrosion issue, normal fuel combustion produces water as a by-product, so I am not sure whether it would significantly change that.

I assume you have heard of simple water injection schemes for ordinary 4 bangers? That does something like the same thing, but you are limited to a 5% mix of water in the gas, more water than that and it adversely effects the combustion process, but it does give more power per stroke. I saw an old motor trend mag from way back that took a corvair, remember those death traps?, stock corvair and injected 5% water and it went 160 odd MPH.
Or so they claimed. What I wonder is, why don't they do that to every car, not sure how much the gas MPG would go up. It should since you are getting extra power in the form of steam which logically speaking should be able to get the same amount of power with less fuel being injected but don't know the numbers. Anyone see any of that data? If you could even get 10% better mph that would be a huge thing in the nations consumption of oil. So what if you combined water injection AND this new fuel device? 30% increase in mpg?