The Hindu Business Line : Air filters: Making cars breathe easy

Poor quality of air intake leads to a dramatic drop in engine performance. Air filters act as a strainer or sieve to keep out ambient impurities from reaching the combustion chamber.

— S. Muralidhar

Performance air filters in high-end cars.

Despite having some of the most stringent emission norms in the world for privately-owned vehicles, increasing levels of pollution from the dramatic increase in the number of vehicles on the road is a concern for all us. The worsening air quality in many Indian cities is leading to a spike in respiratory illnesses among residents of the big metros.

If the poor quality of air affects the health of people, can cars be immune to bad air? After all, vehicular engines also need to breathe. The poor ambient condition of Indian roads is the reason why the engine oil quality deteriorates much ahead of the averages that vehicles in other markets clock. If we need to protect ourselves completely from the pollution, we will need a full-face mask with multiple filters and possibly even an oxygen cylinder. In a car, the air filter does the job.

It may seem odd, but the quality of air that the car’s engine breathes is actually better than the average quality of air that we breathe in the car cabin. In the absence of a cabin air purifier, this will be the case even if the air-conditioner has been turned on.

Internal combustion engines need a mix of air and fuel to perform. During the process of combustion, the air that is fed into the engine has to be free of impurities and rich in oxygen for the combustion cycle to be complete and for ensuring that the burnt fuel has the least amount of wasted fuel.

While driving, if unfiltered ambient air is fed into the engine for sustaining combustion in the engine chamber, then the contaminated air, which could be carrying particulate matter such as dust, pollen and other airborne impurities will also enter. The level of impurities in the air varies from city to city and country to country. But, eventually, with these impurities the engine will be dirtied, the catalytic converter will be damaged and soot build-up will clog the engine and kill it swiftly.

Poor intake air quality will also lead to a dramatic drop in engine performance; just like how good intake air quality improves performance. Poor air quality will lead to the fuel in the engine not burning up fully. There will be an increase in soot, an increase in other emissions, drop in fuel efficiency and a reduction in the life of the engine.

Dirty engine = dirty combustion

In order to support combustion with fresh, clean air, a special air filter is used to act as a strainer or sieve to keep out ambient impurities from reaching the combustion chamber. Good air filters should be able to keep out dust that is as small as a tenth of a micron in width. For comparison consider the fact that the human hair’s diameter is about 100 microns.

In a car, the air filter is usually housed in a plastic container that is attached to the air-intake manifold of the engine. A special type of sturdy, heat resistant plastic is used to construct the air-filter box and piping that feeds fresh air into the engine through the filter so that they can handle the rough conditions in the engine bay.

Most passenger cars use two main types of air filters. The debate about which of the two is better continues, but essentially, most air filters use paper or cotton gauze and they are used by most manufacturers and after-market participants. There are only a few high performance air filters manufacturers who have tried different materials or a mix of these.

Almost all of the cars that we drive, which fall in the mass-market category, use paper air filters. Some cars in the luxury or performance category may be using a different type of filter for increased engine protection and boosting performance. Though a contention that is often challenged, the other popular type of filter, the oiled cotton gauze air filter, is generally considered better. It is considered less porous and more capable of filtering finer particulate matter.

Even better, it is re-usable after cleaning, servicing and re-oiling. But oiled cotton gauze filters are more cumbersome to use. Paper filters have to be replaced after they become dirty or clogged. They cannot and should not be re-used.

Performance filters

All this brings us to whole issue of performance air filters. What are they and do they really offer any tangible benefits?

While discussing the process and performance of the IC engine, one term that is often used is the ‘Stoichiometric ratio’. This is the measure or the ideal ratio of fuel and air in the mixture that is fed into the engine’s chamber for near perfect combustion.

By increasing the airflow into the petrol-driven engine with the use of special high performance air filters and intakes, the performance of the vehicle can be boosted.

Just as in a turbocharged diesel engine, where the turbocharger does the job of pumping in more air, in the petrol engine the effect can be achieved to some degree by the use of a performance air filter.

When the engine receives an increased flow of air, the electronic control module (ECM) senses the higher percentage of air in the combustion mix (air:fuel) and directs the injectors to increase the level of fuel that is fed into the combustion chamber in order to match the preset Stoichiometric ratio.

This in turn leads to an increase in the power generated by the engine, even as the increased amount of air leads to a cleaner, more complete combustion.

Further, just like in a turbocharged diesel engine, performance air filters, in addition to boosting the peak performance of the petrol engine, could also lead to an increase in fuel efficiency and a lowering of emissions.

But, of course, the benefits will tend to taper off, when the focus of switching to a performance air filter is only to achieve a big jump in the engine’s peak power and performance.

Better at the job?

One of the most hotly debated topics about performance air filters is whether they are worth their steep price tags and whether reusable filters like oiled cotton gauze filters actually lead to a better filtration process or whether it just leads to an increase in the level of airflow reaching the engine.

Standalone, performance air filters are not necessarily the finest filters. They mostly rely on packaging a combination of bigger air intake piping and a larger, less restrictive filtering surface to offer a performance boost to the engine. Therefore, replacing the factory-fitted air filter in your car with a new performance air filter alone may not be enough to significantly boost engine performance.

More Stories on : Cars | Auto Tech | Pollution

Article E-Mail :: Comment :: Syndication :: Printer Friendly Page