Clean fuel worsens climate impacts for some vehicle engines: study

March 1, 2011, University of British Columbia
Auto-rickshaw being tested for emissions in an Indian lab.

A pioneering program by one of the world's largest cities to switch its vehicle fleet to clean fuel has not significantly improved harmful vehicle emissions in more than 5,000 vehicles – and worsened some vehicles' climate impacts – a new University of British Columbia study finds.

The study – which explores the impacts of New Delhi, India's 2003 conversion of 90,000 buses, taxis and auto-rickshaws to compressed natural gas (CNG), a well-known "clean" fuel – provides crucial information for other cities considering similar projects.

Of the city's more than 5,000 auto-rickshaws with two-stroke engines – a common form of transportation in Asia and Africa – the study found that CNG produced only minor reductions in emissions that cause air pollution and an increase in emissions that negatively impact climate change.

According to the researchers, the New Delhi's program could have achieved greater emission reductions at a cheaper price by simply upgrading two-stroke models to the cleaner, more fuel-efficient four-stroke variety.

"Our study demonstrates the importance of engine type when adopting clean fuels," says lead author and UBC post-doctoral fellow Conor Reynolds. "Despite switching to CNG, two-stroke auto-rickshaws in Delhi still produce similar levels of particulate matter per kilogram of fuel to a diesel bus – and their climate impacts are worse than before."

Published online in the journal Environmental Science and Technology, the study is the first to comprehensively examine the pollutant emissions from small vehicle engines fuelled with CNG. It included significant laboratory testing of Indian auto-rickshaws.

The study finds that as much as one third of CNG is not properly burned in two-stroke engines, producing high emissions of methane, a major greenhouse gas that contributes to climate change. CNG use also produced substantial emissions of high particulate matter from unburned lubricating oil, which can appear as blue smoke.

The findings show the importance of strong scientific data for policymakers and the need to consider small vehicles like auto-rickshaws in emissions reduction programs, according to the researchers.

"If policymakers have information about emissions and their potential impacts, they can make better decisions to serve both the public and the environment," says Reynolds, who co-authored the study with Prof. Milind Kandlikar and post-doctoral fellow Andrew Grieshop from UBC's Liu Institute for Global Issues and Institute for Resources, Environment and Sustainability.

According to the researchers, the study has broad implications for the design of public health interventions.

"Clean fuels are being used in Indian cities for transportation when they could save many more lives if used for cooking," says Kandlikar. "The interests of the rural poor, particularly women and children, are being put below those of the urban consumer."

According to the researchers, several Asian cities have more two-stroke auto-rickshaws than New Delhi. They say the study provides important information to other cities considering fuel-switching programs, especially those in rapidly industrializing cities in India, Pakistan, Bangladesh, Philippines, Thailand, and Indonesia, where major auto-rickshaw fleets exist.

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4.5 / 5 (2) Mar 01, 2011
Never forget the law of unintended consequences. For some reason, this needs to be stressed much more in the area of "green" tech.
4.8 / 5 (5) Mar 01, 2011
What did they expect?

The particulate emissions from small two-stroke engines is mainly because they ingest oil with the fuel to keep the piston and crank from seizing up, and then they burn the oil with the fuel. Anyone with a 2-stroke moped can tell you that. You have to fill a small oil reservoir every few hundred kilometers, or you mix the oil into the fuel in the fuel tank.

Again, people with no idea what they're talking about making decisions that go nowhere because they're idiots.
5 / 5 (4) Mar 01, 2011
Furthermore, two-strokes are fickle creatures that work more like musical instruments than engines. The design is such, that when the exhaust port opens, the gasses enter a conical section of the tailpipe that expands and then contracts. This rapid expansion sucks the exhaust out of the cylinder and creates a vacuum, which when the intake port opens, draws in the fuel all the way through the cylinder and into the exhaust. Soon after, the intake ports close and the resulting "air hammer" effect draws the fuel back into the cylinder. The shape of the exhaust also sends a backwards pressure wave to help. The whole engine works like an acoustic pump.

Problem is, if you change the properties of the fuel, the A/F ratio, the density etc. you change the speed of sound in it, and thus its acoustical behaviour in the engine. It's like blowing helium into a trombone. Fuel ends up in the wrong place at the wrong time.
5 / 5 (2) Mar 01, 2011
A badly tuned two-stroke engine will actually spew fuel out of both ends because of blow-back. I had a friend who tried to fit a homemade "racing exhaust" to his bike, and all he ended up with was his trousers soaked in gasoline.

Lucky the whole thing didn't catch fire.
not rated yet Mar 02, 2011
Natural gas is not a clean fuel it is only a relatively clean fuel.
Look at Rio where all vehicles run on ethanol.
They have no smog and the cleanest air of any city its size anywhere in the world.
Beware the influence of the Oil Cartel in funding research favourable to them.
not rated yet Mar 02, 2011
We keep treating bio fuels and other gases as gasoline substitutes when we need to make them gasoline replacements. If we would make engines designed for the other fuels and the infrastructure to support them it would fix a lot of the problems with cleaner fuels.
not rated yet Mar 02, 2011
Ivory tower eggheads doing rickshaw 2-stroke experiments.

Jeez, Louise!

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