CNG bifuel installation and operation: What you need to know

1. What are the gas delivery systems available to me?
Sequenital Gas Injection Systems (SGI)
By far the most popular for our cars here. Our cars are newish and sport recent electronic fuel injection systems for petrol. So naturally, with its installed O2 sensors, SGI systems are the way to go. Power loss is from 3-5% actually. I do not believe there are systems that induce massive losses of 10% or more.

Single point inductive gas mixer
It is basically a cng carburetor of sorts for carburetted cars. You can use this for our newish cars but you will suffer massive power losses of 10%. I will only give brief mention here. It is not cost effective to convert an old carburetted car for bifuel use.

2. Can turbocharged and supercharged engines be converted?
Yes! cng is 130 octane. High compression from forced induction will result in higher thermal efficiencies. However, this also depends on the engine.

3. So any car can be converted?
Yes. As long as the car uses a spark ignited engine, it can be converted. Petrol is a spark ignited fuel. However, there are some constraints.

So far, the SGI injector rails are either in inline 3, inline 4 and inline 6 configurations. So a three cylinder engine can use inline 3 injector rails. Four cylinder engines use inline 4 injector rails. Six cylinder engines use the inline 6 injector rail. V6 engines use two inline 3 injector rails. So if your car is a boxer engined Subaru, it can't be converted. Ditto with ****el engine cars.

There is reportedly a kit for five cylinder Volvos made of a single inline 3 rail and a inline 2 rail in development. There may be hope for boxer engined car owners.

4. Can a small car be converted?
Yes. If there is enough load space from the boot. This might mean sacrificing the load space of the car. It is up to the user. There are Honda Fits that converted and in Malaysia, Kancil owners sacrifice their entire load space for the cylinder. See an authorized installer to evaluate your car.

5. So how does it really work?
Firstly you have a storage cylinder. This is usually installed in the boot. The gas is delivered through a high pressure gas line that runs under your car to the injector rail. It comes to a pressure reducer/regulator that lowers the 200bar pressure that the gas is stored under to between 2.5 to 25bar. This setting depends on the engine. Bigger engines need higher pressure. My 1.4L engine needs 12.4bar pressure for example. A 1.6L car might require more.

The injector rail delivers the gas via solenoid valves. Since the gas is already under a pressure of between 2.5 to 25bar, the valves just open and shut. There is actually no real injection as the gas just rushes in.

The cng ECU reads your O2 sensors, throttle position sensor and even manifold air pressure sensors. Once in gas mode, it intercepts the signals to the petrol injectors, shuts them down and sends simulated petrol injector signals to your petrol ECU. The gas "injected" is metered and the duration controlled for optimum engine performance.

Please note that the cng ECU does not have a "map" at all. What it does is measure your petrol injectors pulse time and substitutes a corrected natural gas pulse time for the cng injectors. This has serious ramifications as I will address later.

In your cabin, you have a tiny LED cng level indicator that doubles as a switch. You can switch between petrol and cng operation. You also use this to force start the car in cng. Different systems will use different methods. Ask the installer how this is possible.

This LED indicator is not that accurate. The engine bay itself has the actual gas pressure gauge that sits next to the fill valve. Some installers don't even install this. Check with them. If you are paying that much, might as well have this gauge installed in the engine bay.

6. Dumb cng ECU
This is the serious ramification. The cng ECU is a dumb automaton. It is basically a pulse converter. It reads the petrol injector pulses and then substitutes it for cng injector pulses with some corrections.

The tuning technician then modifies some values to achieve driveability and power. He will also modify it to achieve certain emission standards by observing the lambda reading from the O2 sensor.

Now if you have bought a new lemon car with some faulty components, don't blame the installer. Its not his fault when the car is already garbage from the beginning. Chase your dealer to fix the petrol operation.

7. What if I have piggyback ECU installed?
The cng ECU will attempt to replicate the performance from your piggyback ECU. Remember, the cng ECU is nothing but a pulse converter. Piggyback ECUs do what is known as "remapping". The petrol injectors will have different pulses and these pulses are still copied by the cng ECU.

8. Where should I locate the gas fill valve?
It is really cool to have the gas fill valve at the petrol fill port. The usual norm is to locate it in the engine bay. Having it on the petrol fill port is not without problems. Firstly, the petrol fill port has to be large and the construction sturdy to fit it there. Then there is a problem with leaks. If gas fill valve is leaking, it will most likely leak into the cabin.

Having it in the engine bay solves all of the above. The gas just leaks out and floats away.

9. Should I do anything to ignition systems?
Yes. Keep it top notch and well maintained. There is no need for Nology, MSD or Magnecor stuff. If the car is new, it should drive normally with no hesitations or jerks. If it does, it is either the tuning or ignition system at fault.

Gas is very intolerant of minor ignition faults. Old wires, failing coils and worn plugs can be felt in the driveability of the car in cng mode. On petrol, these components if with some minor faults do not affect driveability.

Ignition wire sets are rated to 100k km. Replace them with OE wire sets. If you cannot find OE wire sets, use direct OE replacements. Stick to the good names of Bosch, NGK and Denso. Coils are also rated to 100k km. You should change them by 100k km too.

Now spark plugs are a little subjective. I'm using cheap regular non-precioius metal OE plugs. I see drastic improvements when I change the coils and wire set. If your car uses Iridium or Platinium as OE, stick to them.

Finally, the plug's gap is important. Gas is very difficult to ionize. So producing a spark needs lots of juice. Your coil works hard. You have the option to gap them slightly smaller so that your coils don't pump out so much juice to fire them. Most cars use 1.1mm gaps for their spark plugs. Reduce them 0.9mm if necessary. No smaller or your petrol performance will suffer. My car is using one coil for two plugs. So I gapped them to 1.0mm. I doubt coil-on-plug systems in the newer cars would need reduced gaps. They are really powerful ignition systems to begin with.

10. How about O2 sensors?
If your car is new. Its alright but if your car is a recently warranty expired car, get a new one. Remember, the petrol ECU reads them and adjusts petrol fuel trim for the injector pulses. The cng ECU copies the injector pulses. Bad O2 sensor will result in bad tuning.

11. What about heat?
Petrol has 47MJ of energy released when combusted. Natural gas burns with 54MJ of energy released. So cng will tax your coolant systems. So keep that coolant system well maintained. There is no need to increase the water component in your coolant. Stick to the regular 50/50 mix with antifreeze. Coolant systems in cars are overengineered. Make sure your fans work and have them replaced when they give signs of being worn.

12. Does the installed system need maintenance?
I'd be lying if I say they don't. The injector rail is made of solenoid valves. These are electromechanical valves that will get worn. The gas fill valve has this spring ball valve in it. It will get worn as well. Listen for hisses after you have filled gas on this port. Most fill technicians will warn you when they hear something. The whole system should be inspected by the installer once a year. It costs nothing for the inspection but the replacements do.

13. How do I shut the thing off when I hear hisses or smell gas?
The cylinder has a valve and the gas fill port has another. Shut both off and visit your installer as soon as they open for business. Make sure you turn the cabin switch to run on petrol as well. You will stall if you don't make the switch.

14. Start on petrol or idle on petrol?
Either will do but I suggest start on petrol, idle on gas. Firstly, as a bifuel car owner, your installation isn't exactly cheap to begin with. So you should work towards an ROI as fast as possible. No doubt cng prices have risen, petrol prices have risen as well. I would say the time to ROI should be about the same as a year ago when prices are lower. I would need figures for this calculation. If the prices of cng didn't go up and remained the way they are and petrol prices are what they are now, you will get an ROI really fast.

The first reason to start on petrol is simple. You car is originally petrol fueled. There are petrol delivery components in your car. Your injectors and your fuel pump. All of them need to run to keep them in ship shape. Petrol has now become your secondary fuel but that doesn't mean you neglect the delivery systems for it.

The second reason for starting on petrol is a legacy issue. When gas is compressed, it will generate heat. Your gas cylinder will feel really hot. Try touching the cylinder after you have filled it with gas. When the gas is fizzing out depressurizing as it is being delivered to the injector, it absorbs heat. The gas cylinder and delivery lines will become cold. The gas regulator taking the brunt of it. In countries experiencing winter, the gas regulator will freeze up and gas pressure lowers until it is undeliverable to the injectors. This leaves your gas powered car sputtering. Starting on petrol allows the car to warm up the cooling system. Warm coolant is supplied to the regulator to warm it up for gas operation. This coolant connection is not done for our local cars but do start it on petrol for the first reason above.

Also keep some petrol in your petrol tank not only for emergency purposes. Your petrol pump is cooled by immersion in petrol.

15. Why is Jln Buroh and Jurong Island cheaper than Mandai?
Simple. The first two are run by a wholesaler while Mandai is run by a retailer. Jln Buroh and Jurong Island is run by SembGas. Mandai is run by SMART Energy.

16. Where are the NGV stations in JB and Malaysia?
Check the NGV Locator:

The fill nozzle in Malaysia can be used for Singapore installed cng systems. To plan a trip up to Melaka or KL, the northern most fill station next to the NSH is Senai. Take the Skudai highway up and into Senai Airport. The only Petronas station there is the NGV station. Fill and enter the NSH. Exit Ayer Keroh, pay the toll and the first Petronas station after exiting the toll is an NGV station. Fill there and then re-enter the NSH. KL and the Klang area has many NGV stations. There are no NGV stations from Ipoh upwards to Penang.

There is an NGV station in Penang itself. There is one in Hattyai should you plan to drive all the way into Thailand.

cng costs MYR0.68/kg in Malaysia. Don't make direct comparisons. Their gas is mined domestically. This is unlike their petrol where they still have to buy from refineries. It is also subsidized but not as much as petrol since cng is a domestic product. The Malaysian government halves the road tax for bifuel vehicles. Malaysian bifuel vehicles also enjoy better toll rates on their highways.

Don't use the Find NGV Installer.

17. Why not use the Find NGV Installer? Its cheaper to install in Malaysia.
Your cng bifuel installation has to be approved by LTA. You have to go for an inspection to approve the installation. Next, you have to register your car as bifuel. All this is done by the dealer if you are buying a new cng bifuel car. If you are installing your current car, you have to go for the inspection and change of vehicle status yourself. Your installer will do the paper work.

18. Why is that green diamond sticker needed?
Safety. When a bifuel car is involved in a serious accident, SCDF personnel will take precautions. In mangled wrecks, you can't just open doors to let trapped occupants out. Rescuers cut cars. If they cut the high pressure line, that's it!

19. How crash worthy the cylinder?
Don't worry about the steel cylinder. Forget Hollywood hype. 9mm bullets from a Beretta can't penetrate a lowly LPG cylinder let alone an able to withstand 3600psi cng cylinder. There is a safety valve on it that vents when temperatures go too high should your car be caught on fire. cng cylinders don't explode on impact. Insist on the engineering certificate if you are unsure.

Composite cylinders are another matter. I don't have experience with them. I know that filling them for the first three times is a pain. It has to be done gradually. They are not cheap either. Costing as much as half the price of an entire steel cylinder sytem installation. Their capacity is pretty small too.

20. What kind of range and economy can be seen?
On average most cars use 5.3kg/100km. A 60L water capacity cylinder holds 10kg of cng. So it is around 180 to 200km range.

21. What are the conversion factors
Kilograms natural gas x 1.496 = Litres petrol
Litres petrol x 0.669 = Kilograms natural gas.
Therefore, $/kg cng x 0.669 = $/L equivalent of petrol
Therefore $/L petrol x 1.496 = $/kg equivalent of cng

22. What is Spritmonitor
Spritmonitor is a free online vehicle costs analyzer. You can feed in your cng and petrol fillings. Maintenance, insurance, road tax and accessory costs can also be added for a bigger overall picture. You can track which accessory or maintenance item has boosted your fuel economy performance or dragging it down. When filling fuel, take the receipt and write down the odometer reading on it. Write down the trip meter reading as well if you reset it to track distance traveled on cng.

Registration is free and I have petitioned the webmasters to include SGD and MYR currencies. Address is click the Union Jack for English.

EDIT 21 Jul 2008: Conversion to get $/L equivalent of petrol and $/kg equivalent of cng. So that users can get a better perspective on the prices.

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