This is the question looming over the minds of all those commuters with cars having petrol engines who:
- Are finding the ever increasing prices of petrol unacceptable.
- Want to spend their resources sensibly.
- Want an environmentally friendlier fuel.
Since late 70s people have been converting their engines to run on LPG (Liquified Petroleum Gas). Increase in fuel prices has also pushed people toward retrofitting Diesel engines in their cars. Now, with the availability of CNG (Compressed Natural Gas) becoming common these days, many vehicles are being converted to it.
All of the fuel alternatives mentioned above have some advantages and some drawbacks. The purpose of this article is to bring those facts to light so that anyone planning about the conversion from Petrol to any other fuel types makes a well informed and sensible decision.
The economic comparison of various alternative fuels is based on the following table:
Petrol Diesel CNG* LPG*
Cost, Rs/ltr 46 28 5 5
Km driven daily 100 100 100 100
Fuel consumption, km/ltr 11 15 3 3
Fuel used/day, ltr 9 7 33 33
Cost of fuel/day, Rs 418 187 152 167
Cost per month, Rs 10,873 4,853 3,939 4,333
Cost per year, Rs 130,473 58,240 47,273 52,000
Savings per year (compared to petrol), Rs 72,233 83,200 78,473
Additional initial cost, Rs 150,000 30,000 15,000
Payback period, months 25 4 2
* For LPG & CNG, the unit of volume is kg.
The conversion decision is based on the following parameters:
- Price of fuel
- Price of conversion
- Payback period based on average driving
- Ease of fuel availability
- Ease of maintenance
- Increase in scheduled maintenance frequency
- Safety
- Ease of cold starting
- Noise, vibration & harshness (NVH)
- Environmental pollution
- Power as compared to petrol
- Luggage space
- Dual fuel operation capability
- Future prospects
The details are:
Price of Conversion:
CNG is stored at a high pressure (approx. 3000 psig). Because of this the piping and equipment is high pressure type and hence expensive. Whereas LPG is stored at a lesser pressure and hence requires less expensive materials. This is the main reason for LPG conversion to be more economical than the CNG.
Safety:
When LPG & CNG were introduced, there were fears of tanks exploding during accidents. New Zealand, Holland & USA have close to one million vehicles running on these fuels for over a decade now and there are no more hazards associated to having a CNG/LPG tank in the car than having a fuel tank in it. So, the bottom line is that both these fuels are reasonably safe to store inside the car.
Environmental Pollution:
The main problem with diesel engine is the emission of black smoke “soot” (technically called Particulate Matter) which is a major cause of health concerns e.g. Asthma and is also a suspected carcinogen (cancer causing). Diesel engines are nearly smokeless when new, but moderately old engines start emitting high levels of smoke. (Latest diesel engines with particulate filters are changing this.)
Environmentally speaking, the diesel engine is the most polluting, followed by petrol engine and then CNG/LPG.
Power:
None of the fuel sources listed above provide more power than petrol. As a result, the conversion to these fuels results in reduced acceleration (pick-up) of the car. Diesel gives the worst acceleration followed by LPG & CNG.
Dual Fuel Capability:
The combustion characteristics of CNG are markedly different from petrol and as a result the petrol engine has to be tuned to CNG characteristics which then makes running the car on petrol difficult and a constant headache.
Although the combustion characteristics of LPG too are different from petrol, it is not as different as CNG, so a car with a professionally installed LPG kit will be able to run on petrol without a problem.
Ease of refueling:
You can fill up the car with Diesel just like you would for Petrol. No special techniques are required and it is hassle free.
For CNG, refilling requires opening up of the hood and is almost as easy as Diesel.
The worst of all these sources as far a refueling ease is concerned is LPG for which you have to remove the empty cylinder and install the filled cylinder, which is heavy. The agencies of LPG are usually located out-of-the-way. Unless you can have LPG filling stations which can refill the cylinder without removing it, this will be a cumbersome process.
Future Prospects:
In the foreseeable future, the alternate fuels (CNG & LPG) will continue to be a sensible choice because of their lesser polluting characteristics and economic benefits. The price of gas is planned to be increased by 300% in the coming years so keep this factor in mind also before converting.
NUTSHELL
• If more than 70% of your driving is long distance & more than 100 km per day, Diesel is your best choice.
• If more than 70% of your driving is within the city, you drive 50-70 km per day and ease of refilling is of prime importance to you, then go for CNG.
• If more than 70% of your driving is within city and you drive 20-40 km per day, LPG is for you.
• If you drive less than 15 km per day, stick to Petrol as the initial expenditure and retrofitting is not worth it.
SUMMARY
CNG/LPG details:
Cost of cylinder filling, Rs= 250 225
Size of cylinder, kg= 55 45
Avg Fuel economy per cylinder, km= 150 150
Driving area = City City
Diesel CNG LPG
Increased Maintenance frequency Y N N
Mechanics easily available N N N
Fuel easily available Y N N
Decreased Environmental pollution N Y Y
Increased noise, vibration Y N N
Loss of power, pick up Y Y Y
Poor Cold starting Y N N
Compromised safety N N N
Luggage space reduced N Y Y
Low pressure system - N Y
Ease of refuelling Y Y N
Good dual fuel capability - N Y
Sorry about the data in the tables, the formatting gets all haywire here. The site doesn't allow PDF or WORD or EXCEL attachments, otherwise would have posted that. Anyway.
