Upping the octane for emergency power

Today I was discussing with a relative about how to make his boat safer for barred inlet traversing. The talk centred on what could be done to give greater assurance that in the event one of his outboards failed ( the motors are past their prime, and even if they weren't, planing cleanly with one of the twins out of action is marginal), to give a temporary boost for a minute or two to safely clear the break on the run in, which would require near enough to 20 knots imo. This might be achieved by having a small tote tank of fuel to which could be added an octane booster, which could give a few hundred more revs at least. Any thoughts about this idea are requested, and any candidate for the magic additive ?

 

Why does he need 20 kts to 'clear the break?'

The additives are easy.

The why is what makes me wonder.

Bad equipment is dangerous. Boosting power on old equipment is not any safer.

 

Long swells travel deceptively fast, to not fall off the back of them you need at least the ability to reach 20 knots on flat water, imo. Old equipment or not, twin engines doubles your chances of an engine failure. What is the additive you say is easy ?

 

upping the octane most likely wont do anything except help prevent an issue with low quality fuel or overloading like when you run a twin rig on one engine which is the best way to kill an engine especially a carby 2 stroke
PS I know the bar issue my parents had a holiday house at Mallacoota

 

thats why all passenger jet aircraft have one engine??? lol

 

Fuel quality is expressed as the "octane number" even though no octane is present, like in LPG that is just a mixture of butane and propane however has an octane number near 100.

The original additive to increase the octane number was the now banned tetra-ethyl-lead. Several commercial concoctions are available for the owners of vintage cars with high compression engines.

To temporarily increase the output of gasoline engines, injection of nitrous oxide (N2O) is used.

 

Water injection could help and alcohol too. Typically you'll also need to toss in some more ignition timing to take full advantage.

 

"Octane" rating measures a fuel's resistance to pre-ignition/"knock". It is not a measure of specific energy of the fuel. Higher octane fuel may have lower specific energy; for example adding alcohol increases the octane rating but decreases the specific energy of the fuel.

Power can be increased on many engines by advancing engine timing but the minimum octane rating needed to avoid pre-ignition will be increased. Engines with "knock sensors" may have increased power when a higher octane fuel is used because the engine control system will be able to advance timing while avoiding pre-ignition and thus increase power.

Nitrous oxide injection is a common method used for temporary increases in power. However it increases engine component stresses and temperatures and increases the probability of engine failure.

 

Thanks for all answers. Right, well, I am obviously not au fait with this business of octane rating Vs specific energy. What is required is an increase in power output, which may be more difficult than I thought, by fuel additives. I am not worried about destroying the innards of a motor by overstressing, it won't be required to perform this way for more than a minute or two, if ever. I should point out that these are carby two-strokes.

 

As others have pointed out, there is no gain, and probable losses running an octane greater than that spec'ed. Engines run best on what they were designed to run on.

The only thing you could do is re-prop for the worst case scenario and accept some small (probably very small) loss in efficiency the rest of the time. Might loose some top end though.

Anything else you try to do just probably won't be there when you need it.

 

In the dim past I did go down in pitch with the props on a twin rig because it would struggle to plane on one engine, but the results were little different. I wouldn't bother trying it again. Hence this brainwave !

 

what you really need is that switch that Mel Gibson had on the Intercepter

 

Mel's interceptor switch seems very real compared to the guff on this site:
http://www.veryimpressiveproducts.com/boat.html
I am particularly taken with this one:
Hull Booster - HB

Increase strength and stability of your hull, improve handling and safety and reduce cabin noise.

The Hull Booster (HB) boosts the strength and stability of the hull.The EUPHORIA TECHNOLOGY™ aligns all parts of the construction, boosting their strength and simultaneously reducing mechanical vibrations.

 

Probably better to get one of these jobs. Keep it stowed with the life jackets and when you need some extra kick.. strap it on, get a good grip on the steering wheel and squeeze the trigger.

Best do a bit of practice first, to get the timing right and obviously make sure nobody is standing behind you when you squeeze.

 

as stated, the octane rating has nothing directly to do with power output. it has to do with fuels resistance to knocking (preignition)

One way to get a temporary power increase would be by installing a nitrous oxide injector. You can buy these system cheap off of ebay, or at your local hot-rod shop. It injects more oxigen into the engine, making a smaller engine act like a very larger one. It will put higher loads on all of the parts, so it is not something you want to do very often. For example, if you could double the power output with NOx injection, you also double the stress on all of the parts, the drive train, the engine mounts, etc.

But this would be a simple and inexpensive way to get a short burst of power out of the existing engines.