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These are testing times

Autocar India conduct emission tests to see which car gets most dirty with our roads. It's like a video a game whose objective is to follow the graph so you continue at the correct speed.

autos Updated: Aug 11, 2010 20:00 IST

We conduct emission tests to see which car gets most dirty with our roads. It’s like a video game.

The objective is to follow the graph so you continue at the correct speeds. There’s a screen in front and you have to accelerate, change gears, brake and stop in a way that keeps the moving cursor on the straight, on a graph that plots speed versus time.

Accelerate too hard, or brake too late, and the cursor slips out of the tolerance zone. It’s not easy. With no road movement, you tend to accelerate faster. But it’s key to anticipate the gear changing and braking. This test can make or break a new model.

In the lab
The Indian Driving Cycle (IDC) is a laboratory test on a rolling road which simulates an Indian driving environment. Every car in India is measured for exhaust emissions with this system. The IDC is also the platform for fuel efficiency figures which car manufacturers will now voluntarily disclose.

At the heart of this test is a chassis dynamometer with a rolling road on which a car is driven. But to make it seem like the vehicle is running on road, air drag and mechanical friction are measured. The inertia of a vehicle is also factored in.

Each model has its own values and has to be tested individually. The lab temperature is kept around 25 degrees Celsius. And the vehicle has to be ‘soaked’ in this environment for eight hours.

Once this process is complete, you can start. A huge tube is attached to the tailpipe to measure exhaust emissions. The report card tells you which cars are dirtier, and which are cleaner. But the public never gets to know the details.

To be on Indian roads, cars simply have to pass. But by how much? Which ones scrape through? Which ones pass with flying colours? We aren’t privy to such information.

Real efficiency
Luckily, it’s a different story with fuel efficiency. So how is it calculated? The very same exhaust gases that are emitted are measured for fuel consumption. Once the breakdown of the gases is available, a formula is applied to arrive at fuel efficiency.

Glance at the official figures and you’ll want to take them with a pinch. Most cars in the IDC (see chart) have recorded kpl figures in their 20s, but it’d be different in traffic. Now you need to study the IDC.

The cycle lasts 1,140 seconds and covers 10 kilometres. There are stops and starts, and the fuel saver is the lack of engine revving. But consumption is worse in the real world. If anything, the IDC figures allow for consistency thanks to the highly controlled test environment.
Autocar India.

First Published: Aug 11, 2010 11:48 IST