As I also mentioned in my blog,
for small hydrogen leaks, buoyancy and diffusion effects in air are often overshadowed by the presence of air currents from a slight ambient wind, very slow vehicle motion or even the turbulence from the radiator fan. In general, these wind currents serve to disperse leaked hydrogen even more quickly with a further reduction of any associated fire hazard.
However,
When hydrogen (or HHO) is stored in pressurized tanks, and if desired to be used as a fuel, the propensity for hydrogen to leak necessitates special care in the design of the fuel system to ensure that any leaks can disperse with minimum hindrance, and the use of dedicated leak detection equipment on the vehicle and within the maintenance facility.
A tank for this purpose will have to be much more stronger than the one which is used for CNG and of a considerable size. Read below to see what should be the size of the tank you will have to eventually make.
Let us take five fuels as an examples here, Diesel, Petrol, Propane (industrial version of LPG), CNG and HHO
The energy density of respective fuels are as under: Let us take its state as liquid in all examples for the sake of comparison here.
Diesel: 843,700 BTU/Cubic Feet (As liquid)
Gasoline/Petrol: 836,000 BTU/cubic feet (As liquid)
Propane: 630,400 BTU/Cubic Feet (as Liquid)
CNG: 561,500 BTU/Cubic Feet (As Liquid)
Hydrogen (HHO): 227,850 BTU/Cubic Feet (As Liquid)
This energy density is a measure as given above is to show how closely hydrogen atoms are packed in as a fuel. (Hydrogen is present in all above fuels).
To make it more clear, I have tried to take a comparative example of the fuel tank. We will have to think big here as you will understand as you read below:
A 500-Ltr diesel tank containing 400 kg of fuel is equivalent on an energy basis to a
8000 L volume of hydrogen gas at 3600 psi (250 bar), although the weight of the hydrogen is only
150 kg, representing a decrease in fuel weight by a factor of about 2.8.
The same diesel tank is equivalent to a
2100-Ltr tank of liquid hydrogen. This is a 4.2 times increase in volume.
If hydrogen is stored as a
metal hydride,
every kilogram of diesel fuel is replaced by approximately 4.5 kg of metal hydride to maintain the same hydrogen/diesel energy equivalence. Thus the same 500 Ltr diesel tank containing 400 kg of fuel would have to be replaced with a hydride tank containing
1725 kg of “fuel” mass 
. For the benefit of all of us here on this blog, no one has even a car that weights that much unless it is a fully loaded Truck (Tata, or may be Volvo). Boston University some years ago also researched on this subject and concluded that use of nano-fibers to store hydrogen could be an answer, however, I have not been able to follow up on how far they reached on this.
For the time being,
for the sake of almighty 
, let us not talk about Hydrogen tanks unless there is someone trying it out with sucess, in which case he should be in NASA and not here.
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Naveen following is for you in particular:
As regards the power: I have not measured it on a roller chassis dynamometer yet, but will shortly do, it and give more info on this once done. However the
increase of power is noticeable, I feel it is about 20-25% increase. On my return from Chandigarh a week ago, I could put an Octavia to shame with my small Wagon R, but this was no race, it could have been an looser driving the scoda instead.
I am keen to learn from you on three areas as below:
1) Ignition timing by a Timing retarders. Could you write more on this explaining in detail as to how you retard the ignition.
2) Are you using parallel ECU? Are you not modifying the existing signals of ECU?
3) I would love to learn on how different your design of HHO conversion is in comparison to what I have done
and explained in detail here. It is probably my turn now to learn from you guys. Thank you all in advance for the same.
Anjeel Babbar