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Old 04-21-2012, 03:07 PM   #41 (permalink)
chrisoverson
The Mad Technician
 
Join Date: Apr 2012
Location: Devon, England, UK
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Rover - '98 Rover 218 iS
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Ok, I'd really like to understand what's going on here, so lets look at it a better way if we can please... as this data seems very confused.

Lets take a closer look!

This should really be simplified, as there seem to be many different arguments here.

1) the speed HHO/Hydrogen can be produced
2) the electricity required to produce it
3) how much the engine can actually use it, or if it can use it at all

Let's totally ignore those first two points for a moment, as that's something to overcome later, and it does not really matter if the third point proves HHO totally useless.

Now let's create a specific scenario to test the numbers. If when cruising at 60mph @ 2700RPM the car gets 50mpg (uk measurements), which is equal to 0.02 gallons used per mile. This equates to around 0.09 litres. Because we are travelling at 60mph we are doing 1 mile per minute, thus each minute the engine consumed 0.09 litres of fuel.

Say we use this on a standard gasoline engine. How much hydrogen does the car need in order to fulfil its supply needs? Simply put, if we completely forget about how to get the hydrogen in the first place and all the other factors and focus on one point at a time we might come to a conclusion more easily.

So, can a car (take for example my 1.8 litre 4 cylinder engine) actually use hydrogen in place of, or as well as standard fuel to carry out its normal operation?

Looking at Wikipedia, the energy density of Hydrogen is 0.01005 MJ/litre. Gasoline has an energy density of 34.2 MJ/litre.

At this point please forgive me if my maths is incorrect, I did not study Physics or Chemistry and am simply going from what I have learned myself since leaving college.

From these figures we see that for every litre of gasoline the car consumes, it needs 3402x the amount of uncompressed hydrogen gas to provide the same energy.

The first question is can we even fit this in the cylinder to be burned?

Fuel usage is 0.09 litres per minute, and RPM is 2700, so for every full revolution 0.0000333 litres of fuel is being used, or 0.000008325 litres every induction stroke (8.325 microlitres).

If we multiply that by 3402 to see how much hydrogen we need, we find that every induction stroke requires 0.02832165 litres of uncompress hydrogen gas, which is a lot. On a 1.8l engine the cylinder size would be 0.45 litres maximum, so at least so far at this engine speed and fuel usage it seems we are onto something. You can theoretically fit enough hydrogen into a cylinder on each induction stroke to replace fuel.

Assuming the same 14.7:1 ratio still applies, you have to add 0.416328255 litres of air to the cylinder to burn. This is only just possible, and the mixture may have to change anyway to use hydrogen in place of fuel, but this is something somebody with more knowledge than me can hopefully answer.

So lets assume for the moment that the engine can use hydrogen as a replacement for fuel, but only just and only when very low amounts of fuel were required anyway.

According to the interwebs, the autoignition temperature for hydrogen is 500 degrees C. The autoignition temperature for gasoline is 280 degrees C. This suggests it is not likely to ignite on it's own faster than gasoline does causing misfire, so here's another point for hydrogen. We know that it can be kept at extreme pressures too, so it's not likely to combust on its own there. It's looking good for the actual usability of hydrogen assuming the first two issues were not a problem.

I'll leave it to somebody else to cover how precisely you can deliver this much gas into the cylinder fast enough, as thats for someone with more experience/knowledge to comment on.

So lets go back to the first two points. If we assume that 3402 times as much hydrogen is used than gasoline each minute, that means we have to supply the engine with 0.409 litres per minute or 24.54 litres per hour however you prefer to look at it.

You can get hydrogen in these quantities, costing around $4 to $10 per kilogram depending upon how it is extracted, which at around 0.071kg/litre is a little over 345 litres.

So, lets assume the upper price tag and say hydrogen works out to be $0.0289 per litre, and around me (south-west england) regular gasoline is 1.42 or $2.287 per litre.

This makes hydrogen a whole 79x cheaper to buy than regular fuel per litre, making it appear brilliant! But when you consider that you require 3402x as much, hydrogen then becomes almost 43x more expensive than gasoline to run your car on.

So far we have found: Hydrogen can be used in an internal combustion engine in place of fuel, but only just, as you have to almost fill the entire cylinder with it when cruising along efficienctly just to be able use it at all when uncompressed. Using it compressed would be pointless as this means the engine has to work even harder on the compression stroke than usual, and would only be useful if lots more power was produced or it was a lot cheaper.

Not looking good so far. If you buy your hydrogen you pay anywhere between 20x and 43x as much for the same power output.

Now, the only possible way hydrogen could be useful whatsoever in an internal combustion engine is if you make it yourself, or buy it much much cheaper. If you are lucky enough to get your hands on huge quantities of hydrogen for a huge amount less than the normal asking price then great! Give it a go! You're still better off using it in a Hydrogen fuel cell car though as it would be much more efficient without all the usual frictional losses, and you'd be able to use it more successfully; as we discovered above it can only just about be used to sustain an engine by filling the entire cylinder.

You should be able to see by now that generating HHO by means of an alternator would be very difficult. You'd have to generate huge amounts of it by using almost no power at all, because adding any load onto the alternator would drop the efficiency rate straight down meaning the hydrogen could not sustain itself, so this is out of the question.

The only remaining possibility is to get the hydrogen by other means. You could generate it using power from a seperate battery, which is then recharged at home. You could also generate the hydrogen at home using mains power, renewable energy in the form of solar/wind/water, or naturally using algae or something similar.

If you can do this, the only question remaining is can you:

1) Produce enough to satisfy the car's requirements
2) Produce it cheaply enough to be justifiable
3) Store it and use it in a safe enough way
4) In the case of home energy usage, make it more practical than just using an electric car charged from home.

If you can somehow satisfy all these requirements, then I see no problem with giving it a try.


To sum up then:
  • You might be able to use hydrogen to run a car in theory
  • You cannot produce it using power from the alternator, or by adding any kind of significant load to the engine
  • It could be useful only if you can create it cheaply, and in sufficient quantities
  • There is absolutely no point if you end up spending more money, or using more electricity than it would take to simply run the car on electricity or gasoline in the first place
  • It is only useful if you can create the hydrogen yourself, as it is more expensive to buy than petrol
  • You would only be able to use it under certain conditions, and it could never replace fuel entirely

I doubt very much all my mathamatics here will have been perfect, so I'll leave it up to the experts to give their advice and opinions here.

I do hope that this will be of use or of interest, and sorry for making it so long, I just wanted to cover everything as it seems to crop up everywhere with no decent enough answers to prove it one way or the other.

Thanks!


Last edited by chrisoverson; 04-21-2012 at 03:12 PM..
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