Suppressed CNG facts

Pollution Watchdog's Study On Fuels Is Full Of Loopholes

The central pollution control board has fumbled in answering a critical question on carbonyl and methane emissions from vehicle exhausts: which pollute less - petrol, diesel, CNG or LPG ?
The pollution watchdog's study on emissions provide a database that could be used to give policy message.It declared CNG to be the worst fuel for four wheeled light and heavy commercial vehicles.But the finding is flawed as it compared factory fitted petrol and diesel engines with retro filled CNG and LPG engines to test the fuel. In retro fitted vehicles, engine is installed at local workshops.
CPCB experimented on two , three, and four wheeled vehicles which operated on CNG, LPG and various combinations of Ethanol, biodiesel, Bharat stage 2 and 3 petrol and BS 2 and 3 diesel. It tested Carbonyl and methane emissions from these vehicles.
CPCB does not mention the vintage of the vehicles used, claiming "unavailability of dedicated CNG engine vehicles." It is surprising because automobile majors such as Maruti, Hyundai, Mahindra and Chevrolet have already launched dedicated CNG vehicles. Delhi and many other Indian cities have banned retrofitted CNG buses.
"The methodology the board used to brand fuels or worst is flawed " as retro fitted CNG and LPG vehicles can never achieve ; all the aspects cannot be optimised, " said PMV Subbarao, wjo teaches mechanical engineering at IIT- Delhi.
Petrol vehicles converted to run on natural gas suffer because of low compression ratio of their engines, while diesel engine conversions result in compression ratio more than necessary. Also the ratio of air and fuel is changed in retro fitted vehicles.
A stringent quality assurance policy on retro fitting is necessary and it can be based only on scientific evidence on emissions from factory fitted vehicles.
Spurious alternate fuel kits fitted at ill-equipped service centres account of 32 % of Indian market. The illegal business thrives as the kit come 30 % cheaper.
The criticism of CNG on its high methane emissions does not have sound basis. Methane exhaust from CNG engines is 12 % lower even if one compares the life cycles of two fuels.
"Unregulated emission cannot be ignored. A reliable database is required to facilitate policy action and promote after treatment systems in Indian vehicles, " said Anumita who heads the air pollution and urban mobility unit at the research and advocacy organisation.

Health Hazards

Carbonyls are produced due to partial oxidation of hydrocarbons that escape from the vehicle's combustion chamber to the exhaust system. Through repeated exposure, carbonyls like formaldehyde, acetaldehyde, acrolein and acetone can cause irritation to eyes, respiratory tract , mucous and skin. Acetaldehyde and formaldehyde are suspected carcinogens.
The study fails to take note of the cumulative effect of suspended particulate matter and carbonyl emissions on human body. Most of these toxic substance enter human body only through air borne particles.
The CPCB study also neglects the higher formaldehyde emission from diesel vehicles. For four wheelers formaldehyde emissions from diesel vehicles are 20 % more than from petrol vehicles.