What is Marine Gas/LPG ?
LPG is an abbreviation for 'Liquified Petroleum Gas' and is also referred to as 'Marine Gas' by some suppliers.
It is a by-product of the refinement of crude oil. LPG is also produced when Natural Gas Methane) is extracted from the gas fields and 'dried' before being piped to homes and industry.
LPG has a unique and very special property:- if mildly compressed it easily changes to a liquid state. This allows a large amount of gas (stored energy) to be contained in a relatively small space. The reverse process is just as fortunate - if decompressed (i.e. allowed to escape the pressure tank) the liquid gas will quickly revert to its gaseous state (vaporise).
In other words, store LPG in a pressurised tank and it will remain liquid, occupying only a small space. Release some of the liquid and it will immediately revert to its gaseous state, expanding as it does so. Liquid Propane expands to approx 200 times its liquid volume when reverting to gas. The reverse applies, as gaseous LPG will 'shrink' by 200 times when compressed and liquification takes place.
There are two basic types of LPG....
- Butane is commonly used as lighter, heater or camping stove fuel and as a propellant for aerosol cans of paint, hair spray, fly spray etc.
- Propane is the gas used for engine fuel as its calorific value (how much heat a given amount of gas will produce when burned) is significantly higher than that of Butane and it "boils" at a lower temperature .
If you release liquid propane into the atmosphere it will be seen to bubble and fizz. The liquid is boiling, releasing vapour (gas) as it does so, just like boiling water releases steam, (vapour) albeit at a much lower temperature. It will do this right down to minus 42 degrees C, which ensures that it will vaporise in all but the coldest climates and conditions.
Other gases (e.g. natural gas) potentially make a good fuel for an internal combustion engine but do not possess this unique property. Thus, far less compressed but non-liquid gas may be stored in a tank of a given volume and the boat's range would be severely reduced.
Vaporised LPG is heavier than the surrounding air if allowed to escape (approx one and a half times heavier). In the event of a leak, the vapour will sink to the lowest level. Care should be taken, as small amounts of leaking gas could make a lethal charge in the boat's bilge area. All that is needed is an ignition source (an electrical spark caused by a fault or maybe a thoughtless owner striking a match for light) and the stage is set for disaster. This is one of the reasons why the HambleMEGS Control System switches on the engine compartment fans when the boat's batteries are first switched on.
Unlike petrol, LPG is in a pure or gaseous state at normal atmospheric pressures and temperatures. It needs very little encouragement to vaporise and lends itself more readily to mixing with air (to get the Oxygen required for a combustible mixture). It needs no fuel pump to get it out of the tank and up to the engine, as the large pressure differential between the tank's interior and the atmosphere does it for you.
The Octane rating of LPG is far higher than that of raw Petrol, thus no Octane enhancing additives are required. Interestingly, in practical terms the only thing added to LPG is the pungent smell, designed to warn us of its presence. In its pure state, the gas is colourless and odourless although it can be seen as 'waves' apparently 'bending' what we can see through it (this is 'refraction').
In economic terms, LPG is cheap to produce (less additives and filtering are required). In the past it has been regarded as a 'waste' material occurring when more popular petroleum products were sought and made. In the UK, and most other oil or gas producing countries, there is currently a surplus of LPG.
In environmental terms, the burning of LPG produces less CO2 and virtually no CO or SO2. No harmful compounds of benzene or lead result from combustion simply because they are not added to enhance the octane of the fuel. Also note that when compared with Diesel, LPG combustion produces NO particulates or ultra-fine particles.
It's not just the environment that benefits - your engine will not suffer the attack of acidic combustion products that increase internal wear and erosion. Engine oil deteriorates at a far slower rate (with LPG) as no acids and almost no carbon deposits are present to reduce its effectiveness. Less oil sludge (and resultant blocking or restricting of crucial engine oil supply drillings or capillaries) is also a large gain. The average engine oil temperature may also be significantly reduced which further reduces oil degradation and reduces engine wear. As for other parts of the boat, the useful life of exhaust components has been proven to be extended by up to three times when LPG is used as a fuel.
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