1.Fuel Tank
2.Carburetor
3.Fuel shut off valve (solenoid)
4.Stage 1 regulator
5.Stage two regulator
6.High Pressure hose and fittings
7. Low pressure hose and fittings
8.Heater hose to regulator.(Expansion of fuel from liquid to gas will freeze the regulator in a high volume situation.
Also,extended "warm-up" of the engine is neccesary, especially in cold weather.)
9.Primer switch (button),(overrides the normal regulator pressures to prevent vapor lock in the fuel system on initial start up) also used to create a rich mixture during cold weather start-ups.
I really don't know what your reasons might be to consider a conversion,but I would let it be as it is.
I thought I was pretty negative in my response to your first question, but here is more:
Availability of fuel on the road (or is this a stationary
engine?)
You cannot legally drive through a tunnel in the USA(or so I understand) with a compressed gas vessel.
I could forsee problems if the exaust system is equipped with a catalytic convertor.
I could forsee problems if the engine compression ratio is above 9 to 1
I could forsee problems if the ignition timing is not
adjustable.
Question- are you planning to use it in the liquid or the gaseous state?. The tank may be used for either application,
but the delivery to the engine requires a compatible system
with liquid or gas.
Keep in mind I am not an engineer. I can only give you my experiences on the subject, as I was formally employed in the lift truck repair industry.
Oh yeah, as if that weren't enough, everyone you come in
contact with,will tell you stink( the smell will get in
your hair and clothes)
There are huge numbers of CNG vehicles in places like Argentina - while they're designed for CNG they don't suffer from problems. I have been driven in a converted car, (in Australia) I was told the conversion went well and there were no problems. There were no cold start problems since the fuel is a gas and doesn't need to evaporate into the inlet manifold. (I think the ignition timing needed tinkering with because the idle was a bit rough)
You don't get liquid natural gas at room temperature, you have to chill it.
I also have heard it's illegal in the US to take compressed gas through tunnels but I think the legislation is written for gas as a cargo not the fuel.
The main cost is that the conversion is quite expensive (at least it is here) and there are few experts who can do it properly, so unless you live somewhere where NG is MUCH cheaper than gasoline you'll take years getting your money back.
Thanks for your information alloyboy(structural)
In Delhi(India)considerable number of engines both petrol and diesel have been converted to CNG operated vehicles according to the legislation passed by the apex court.
Normally diesel engine compression ratio is above 15. But you mentioned that problem may occur if the compression ratio is more than 9. They have converted and successfuly running diesel engine buses. Could you please provide some information about how they are doing this.
I don't know why you think that high compression ratios are a problem for CNG engines. In fact if I was going to run a dedicated CNG engine I would raise the compression ratio to improve the efficiency and power output to make up for the loss in power that is inevitable with a non-turbocharged or supercharged engine. The octane rating (not a complete guide to the potential increase in compression ratio) of CNG is about 115, I think. Better than aviation fuel and without the lead.
Because the fuel is gasified before the carburettor, there is no latent heat of vaporisation to cool the incoming gas as happens with liquid fueled engines. The effect of the cooling is to raise the density of the inlet gas so that you get more in (a kind of supercharging - which is partly why methanol fuelled vehicles are more powerful than petrol fuelled ones as methanol has a higher latent heat of vaporsiation and you need more of it to get the correct air to fuel ratio).
CNG does not need vaporisation as it is just a highly compressed gas and that is a problem as the cylinders to store it need to be very strong = heavy and the volume of gas stored is lower than for LPG which is stored as a liquid and at a lower pressure. The upshot is that the range on a given volume of fuel tank is small for CNG.
In New Zealand there are a fair number of CNG vehicles, and they report better engine life than petrol powered ones due to the lack of nasty additives (scavengers to clean deposits from the engines). I changed the oil on a vehicle that had been running on gas for a year and it looked like it had just been put in, it was clear and golden. I was impressed.
CNG is seen here in the US a the "fuel d'jour" and has the support of many industries, especially where a regulated gas utility is situated.
On the positive side, it is clean burning even in open loop, and very clean when in closed loop. There is no need to worry about your catalyst life if operating in closed loop. Most modern engines do not have adjustable timing, so electronic timing enhancements can be installed to allow a standard gasoline (petrol) engine to use CNG relatively effectively. As for the compression ratio, a good solid 11.0:1 is a good starting place to recover some of the volumetric efficiency loss due to the vaporized fuel.
On the negative side, its an expensive system. The tanks are very costly, and fuel range is limited. CNG is not available everywhere, and where it is, its often at low pressure due to prior vehicle refueling. On the flip side of the coin, the fuel itself is very inexpensive, the most costly part is the compression and storage.
Many developing countries are using CNG as a primary fuel (Bangladesh, India, Pakistan, Turkistan, Uzbekistan, for example) because they have so much in reserve.
Is it a good fuel? Yes.
Is it feasible? Yes.
Is it practical? Yes, with some restrictions.
Is it for everyone? Not quite, but it depends on the existing infrastructure.
Will you be in a CNG vehicle any time soon? You may already have, if you ride in an airport shuttle or municipal bus, its rapidly growing in that market.
