Pinza wrote:Can someone (briefly) explain to me what is involved to convert a CNG bus to normal bus configuration (if at all possible).
Is it just a conversion or a re-engine or is it possible to replace the CNG tank?
From earlier posts it would seem that transperth will have a heap of CNG buses for sale within the next 10 years and it seems a bit of a waste scrapping just because the CNG tank has expired.
Probably a topic that deserves its own thread.
CNG tanks can be replaced. Given they store gas at a high pressure (over 200 bars, but this varies depending on where you are in the world), their construction must be able to withstand pressurisation and depressurisation for the expected life of the tank, thus they are quite expensive. Once expired (CNG tanks have an expiry date on them and cannot be used past that date), the replacement cost may not make much sense considering the age of the vehicle.
I presume the tanks in the high-floor CNG buses were replaced at some point (tanks can last up to 15-25yrs or more, depending on their construction and local regulations), particularly given the political climate of the mid-2000s where gas buses were 'in vogue.'
Earlier vehicles such as the CNG-powered O305s and O405s can theoretically be re-powered with LPG given the simplistic fuelling system they utilised as original equipment. The O405s (high floor or naturally-aspirated NH) were converted to run the Westport Single-Point fuel injection later on in life. Converting to LPG would necessitate doing away with this marvellous upgrade.
I've heard two ex. BT Scania L94UBs have been successfully converted to LPG. Other ex. BT Scanias were re-powered with Cummins diesel and on-sold.
There are several issues with installing a diesel engine in a CNG vehicle with life-expired tanks:
- You need to do away with the roof-top CNG pod; on Volgren-bodied buses it tends to accumulate water in the wetter months
- Sourcing and configuring a diesel fuel tank
- Finding an engine that suits the transmission and other driveline components
- You're dealing with a vehicle that is already older; there will be wear and tear in the chassis, bodywork, driveline components and electrical system. If you consider the modern trend in fleet replacement is 16-20yrs, other major components in the bus may already be life-expired.
- If diesel vehicles of the same make and model are available, cost of diesel or LPG conversion of a gas bus might exceed the purchase price.
With an LPG conversion, the issues are largely the same, except:
- LPG could have a negative effect on engine life
- Cost of removing the CNG gear and replacing with appropriate LPG gear
Pinza wrote:... 1814 and 1819.
Ahh lovely, two of my favourites
