Vehicle conversion FAQ
Compressed air is not mentioned at opengarages. Why is that ?
Air, compressed at 30 MPa (4,500 psi) contains but a mere 0,050 kWh of energy per liter, whereas say gasoline has 8,9 kWh per liter. So, a vehicle that could drive say 700 km with its given gasoline tank (most have about a 50 liter tank (1) -and a consumption of about 15 to 21 km/liter (2)-), could drive only 3,9 km.
A makeshift solution that could still allow you to use compressed air to "some degree" could still be practical though. The method to do so would be by using a conversion kit that would convert the internal combustion engine in your vehicle to allow it to run on either regular fuel or compressed air (so, basically making your vehicle into a flexible fuel vehicle). The internal combustion engine can hereby be made to run on compressed air in the city (where there's a lot of starting/stopping). Compressed air tanks hold very little energy, but it might be enough for running in the city (where the tanks can be refilled fast at regular filling stations -filling stations tend to have an compressor service for inflating tyres, ...)-. The idea here is that a cheap compressed air tank could be added and an electric switch too would be added near the driver, allowing him to switch between the fuels. An additional switch would be added to allow the alternator to be disconnected by it (electrically, not mechanically !). The latter switch would hence reduce the mechanical resistance of the alternator, conveyed unto the engine. The switch would be used when driving on the compressed air (as in this instance, no spark ignition is needed anyway, and any devices that need power can just obtain it from the battery; the battery won't be recharged by the alternator any more, but since the engine can only run limited time on compressed air, it wont be long enough for the battery to get exhausted). This idea is a variant on a similar idea of Leroy K. Rogers
Hydrogen (used as fuel on itself -so not as a booster) is not mentioned at opengarages. Why ?
Hydrogen is often hyped as the fuel of the future, but it still has many problems making its use in vehicles today impractical and not at all ecologic. The main problem is the storage of the fuel itself: to store hydrogen we need either extreme pressure (5000-10000 psi) or extreme cooling (to − 252.87 °C).
So, when applying the cooling technique, we need to have a refrigeration system on-board the vehicle that can cool it to this temperature. This hence requires huge amounts of electricity, which itself needs to be derived from the power the engine (running on hydrogen) needs to provide. If we consider that the efficiency of the engine itself isn't all that great (35% when using the hydrogen in an internal combustion engine), it quickly becomes clear the whole thing is very inefficient (and not to mention costly, as such extreme coolers can't be acquired cheaply).
When applying extreme pressure, it may be possible to use it in a internal combustion engine effectively, but tanks that can withstand that kind of pressure can't be obtained easily, and are again, very costly even if you do find them.
If hydrogen tanks do become cheap enough, we also need to consider that you might still emit some CO² per kWh. This, depending on where the electricity you use to recharge your batteries came from: If coal was used to generate the electricity: you'll emit 1 kg CO² per consumed kWh. If it came from PV solar panels, you'll emit 0,1 kg CO² per consumed kWh. If it came from nuclear power plants, you'll emit 0,006 kg CO² per consumed kWh.
Are there any fuels that are similar to hydrogen (emissionless and not even causing any air pollution at all), but which also don't have the disadvantages hydrogen have (storage problems) ?
Yes. There is formic acid. Formic acid however requires a fuel cell, so can only be used to convert electric cars (allowing them to not require batteries any more). Internal combustion cars can as such not be converted. The fuell cells (DFAFC)'s are also still expensive, and difficult to acquire.
There is also methane. This is similar to hydrogen in that it too is an emissionless fuel (if it's made using the Sabatier process, so from hydrogen), and it causes no real air pollution when burned. Like formic acid, it too stores easily (regular tanks also used in CNG conversion kits would do), and it can even make cars act as (temporary) carbon sinks.
This too is a biofuel, and it's practical. However it is very toxic and can be absorbed by the skin. If absorbed, it could cause blindness. So, we rather avoid it.
What's the difference between CNG and the "biogas" you keep mentioning ?
CNG is a compressed gas. More importantly, it is "natural gas", meaning gas that is derived from cavities under the the soil where it has been locked away for millions of years. It is as such a fossil fuel and contributes to global warming (quite considerably even, it contains 0,6 kg CO²/liter). Biogas is created artificially, using anaerobic digesters, and contains 0 kg CO²/liter.
Hybrid vehicles aren not mentioned neither ?
The reason why hybrid vehicles (3) tend to have a greater fuel economy (km/l) is because people tend to use their vehicles in congested areas (cities, ...). This, as in congested areas, vehicles are stopped and started a lot, and often need to run idle for a considerable length of time. Internal combustion engines consume more under these conditions, but electric engines/batteries do not. A hybrid vehicle can switch to its electric propulsion when in congested areas, and switch to its internal combustion engine when on open roads. So, people that use their vehicle both in the city as on open roads will find them much more fuel economic than non-hybrid vehicles.
1: a 50 liter tank is about a 13 gallon tank 2: 15 to 21 km/liter is about 35-50 mpg 3: the "hybrids" discussed here are hybrid vehicles combining a internal combustion engine with a electric engine