AdBlue! What is it and how does it work in certain diesel vehicles?

Automobile experts and enthusiasts might know about the diesel exhaust fluid called AdBlue. How does it contain vehicular pollution?

The Government of India had brought in stricter emission norms two years ago. As vehicles were upgraded to BSVI emission standards as per the new norms, some vehicle makers withdrew a few of their diesel models. But some others like Tata, Mahindra, Hyundai and Kia came out with BSVI diesel engines. And since then, AdBlue has become a talking point. It is widely held that the exhaust fluid is needed only for engines with displacement above 2000 cc and not for those below it.

Here is a lowdown on what is AdBlue and how it works.

AdBlue is used in most BSVI vehicles equipped with Selective Catalytic Reduction (SCR) technology. As per the BSVI emission norms, all diesel vehicles need to contain the emission of two harmful pollutants — diesel particulate matter or soot and nitrogen oxide emissions.

The emissions are contained with a diesel particulate filter (DPF), a device designed to greatly limit diesel particulate matter or soot from the exhaust gas of a diesel engine, and an after-treatment process known as the Selective Catalytic Reduction wherein an aqueous urea solution called AdBlue is used to reduce harmful Nitrogen Oxide emissions.

When injected into the exhaust gases, AdBlue converts nitrogen oxides(NOx) into less harmful nitrogen and water. It is marketed as AdBlue; though there is blue in its name, it’s a colourless liquid.

The composition

AdBlue is a mixture of high-purity urea (32.5%) and deionised water (67.5%). A separate tank for it has been provided in the vehicle; you could see its lid next to the diesel tank cap.

When the engine is on, through a special setup AdBlue is sprayed into a catalytic chamber fixed in the exhaust pipe just before DPF. This process is carried out with the help of sensors by the electronic control unit.

Where to use

Do engines with a displacement of less than 2000cc need AdBlue?

All diesel engines that comply with the BSVI norms need to have a mechanism to reduce the emission of nitrogen oxides. Small diesel engines (less than 2000 cc) use the Lean NOx Trap (LNT). (LNT is an alternative to the SCR system, the catalytic converter that uses AdBlue.)

LNT is also a catalyst. It is used by small diesel engine makers (Hyundai, Kia) due to the low emission of NOx that needs to be controlled, catalyst regeneration capacity, and low cost. However, Mahindra is using AdBlue even in its models (Marazzo, XUV300) that have the smaller 1500 cc diesel engine.

What is the price of AdBlue?

The average cost of AdBlue is Rs 85. The price could go up or down depending on the brand.

When do you need to top it up? What is the capacity of a standard AdBlue tank?

In small diesel vehicles that use AdBlue, the tank capacity for the catayst ranges from 5 litres to 20 litres. Its top-up is decided by the distance the vehicle has covered, which is provided in the vehicle manual. For example, Toyota advises a top up of its 12-litre tank after 10,000 km.

Is there an indicator for AdBlue level on the dashboard? What happens if the tank runs dry during a trip?

Diesel vehicles have a warning message on the dashboard, alerting that the AdBlue tank is running low. If the fluid reaches the reserve level, the light will glow. It will also show the estimated distance when it will run out, and the distance that can be travelled with the remaining amount.

The vehicle won't stop if AdBlue is over when the vehicle is running. Then the electronic control unit reduces the power of the engine and controls emissions. The vehicle will be run at this speed for some time; this is called limp home mode. The vehicle can be run in the mode till the next place where AdBlue is available. But if the engine is switched off after AdBlue is over, it can't be restarted without filling the AdBlue tank.

(This article is in response to a letter that came to Fast-track, the Malayalam automobile magazine published by the Malayala Manorama.)