[sustran] Diesel vs Natural Gas...

[Jain Alok]

Following recent discussions on LPG and CNG, I thought this might be of
interest to people on this list, which I had saved from discussions on
another list.

Alok Jain


Natural gas vs diesel
There have been a number of references on the list to the supposed 
superiority of compressed natural gas over diesel for buses. The following 
may be of interest
PSam
For Immediate Release
DIESEL OR NATURAL GAS? NEW HARVARD STUDY FINDS ENVIRONMENTAL PROS AND CONS 
WITH BOTH
Which fuel is the right choice for heavy trucks and buses? Its a decision 
facing policymakers in California, at the EPA, and at government agencies 
around the world, as well as executives at automakers and corporations that 
operate fleets of buses or trucks. Phase 1 of a study comparing the two 
fuels, by the Harvard Center for Risk Analysis (HCRA) at Harvard School of 
Public Health, finds that there are advantages and disadvantages to each. 
Environmentally, natural gas is better at reducing particulate and NOx 
pollution. Diesel is better for reducing greenhouse gasses.     Diesel is
the 
fuel of choice now, but concerns about particulate pollution in diesel 
exhaust have prompted a move toward alternatives. The HCRA analysis finds 
that natural gas reduces emissions of fine particulates, those smaller than 
2.5 microns. But natural gas may generate more ultra fine particles than 
diesel. Those are less than .1 micron. Several studies indicate that 
ultrafine particles may have an even more dramatic impact on health than 
those in the fine category.     The study finds that because natural gas is 
primarily methane, a relatively simple molecule, it combusts more completely

than many fuels, producing fewer emissions of several types, particularly 
NOx, an important contributor to ground level ozone and the formation of
fine 
particulates.   The advantages of diesel come from its efficiency. Diesel 
engines convert a large fraction of the available energy into useable work. 
As a result, diesel engines consume less fuel overall than if they were 
converted to natural gas. The HCRA study suggests that converting heavy 
trucks and buses from diesel to natural gas would increase emissions of C02,

a significant greenhouse gas. In addition, the study finds that more 
widespread use of natural gas would likely increase the escape of methane 
into the atmosphere. Methane is approximately 20 times more potent as a 
greenhouse gas than CO2.    The study finds that European regulators seem to

be favoring diesel fuel as part of their effort to comply with the Kyoto 
agreements to stabilize CO2 and other greenhouse gas emissions. They are 
using tax incentives and emissions standards to encourage the use of new 
cleaner-burning diesel fuels. European vehicle manufacturers appear to be 
increasing their application of "green" diesel technology that captures 
significant amounts of particulates.    The study finds that diesel has 
safety advantages over natural gas, which is a more flammable and explosive 
fuel to handle and store. It finds that diesel has a short term cost 
advantage, but that natural gas might end up with roughly the same costs if 
engines and refueling infrastructure become common.

The Harvard Center for Risk Analysis promotes a more reasoned response to 
health, safety, and environmental risks.

    The full report can found at <www.hsph.harvard.edu/press/releases> 
connected to the electronic version of this release that is posted there.
arvard Center for Risk Analysis Harvard School of Public Health
718 Huntington Avenue Boston, Massachusetts 02115 
Contacts: Edmond Toy, lead author, 617-432-1566, etoy at fas.harvard.edu David 
Ropeik, Director of Risk Communications. 617-432-6011, 
dropeik at hsph.harvard.edu