Hello

I am one of those constantly ranting about Bangkok's buses - as a motorbike rider constantly being stuck behind them in traffic jams because they absolutely must use all three lanes of the road to chat with each other, at the same time playing with the throttle to make sure anyone behind emerges with a black face.

The more i am happy to see more and more of the old junkers being converted to CNG - i am talking about those typical white/blue city buses. No more soot! Yeah! Still no fun wasting my time behind them in a jam but at least i can breathe.

But i am curious now - just what type of engine do they use in there? I mean - it's a bus after all. And if i understand the whole CNG-conversion process, they need to swap the Diesel engine to a petrol one in order to run on CNG, because Diesel's don't have the required ignition system. As there is definitely no smoke at all coming from those CNG buses, they must be running on pure CNG, not some Diesel-CNG mix as i have just read about being a possibility.

Now does anyone here know what engine is in there? Must surely be something bigger than in the average car, i mean - they are BUSES.

Appreciate any information.....

Best regards.....

Thanh

Well, I can't answer for BMTC, but here in Bangalore and Delhi (who have the worlds largest CNG bus fleet) the 'CNG' buses are definately CNG/Diesel dual fuel, the proportion of diesel is small as it is required solely to start the ignition process. I would imagine the BKK buses are the same. The CNG apparently also improves the overall combustion process reducing particulate emissions and thus the black smoke

Making a diesel run on CNG is a very complex process involving computer controlled injection systems as the energy value of CNG is variable and getting the mixture wrong results in serious engine damage, that's why, for smaller vehicles, swapping the engine out is the more viable solution. SRT fried several engines a couple of years back when they failed to correctly calibrate their injection systems resulting in the abandonment of SRT using CNG for their trains.

Hi

Thank you very much for the reply. However being stuck behind buses for more than an hour on the average day i can tell you that there is definitely no Diesel involved in those - it's pure CNG.

I found some info yesterday by googling that two companies, one American and one Australian, do the conversions - it seems like they keep the original engines in there and just replace injectors with spark plugs, a spark distributor in place of the Diesel pump and a "carburetor" (that site used that word) in the air intake to feed the gas. If it is like that, it would make sense.

By the way on that construction site in my neighbourhood i saw a concrete mixer truck today that ran on CNG And last night a tractor-trailer on CNG, that one looked rather funny because it had a double-row stack of gas cylinders behind the cab, 5 cylinders tall, 10 alltogether. I hope they will convert every single one of these smoke-belchers into CNG and maybe the air in Bangkok will be breathable again.

Best regard....

Thanh

Sydney (Australia) has been experimenting with this type of bus for about ten years. Recently, it has been decided that these buses replace most of the old fleet.

http://www.sta.nsw.gov.au/environmental_factsheet.php