USE OF UNLEADED PETROL

It is desirable that a catalytic converter has an effective life time equal to half to the car life or at least 2 lakh km. Converters lose their efficiency with age due to thermal degradation and poisoning of the active catalyst material. Just a small amount of lead on a catalyst site reduces HC emission reduction by a factor of two of three. Use of leaded gasoline filled two times (full tank) would completely poison a converter and make it totally useless. Therefore, leaded gasoline cannot be used in engines equipped with catalytic converters.

1 Use of Additives

To improve the combustion performance of fuels, some compounds called additives or dopes are used. The requirements of an additive are as follows:

1. It must be knock-resistant, surface ignition-resistant, or both.
2. It should be stable in storage and have no adverse effect on fuel stability.
3. It should be soluble in fuel under all conditions.
4. It should be in liquid phase at normal temperature and volatile to give rapid vapourisation in manifold.
5. It must not produce harmful deposits.
6. Its water solubility must be minimum to minimise handling losses.

The most commonly used additives are as follows:

1. Tetraethyl lead (TEL), ethylene dibromide (EDB), or ethylene dichloride (EDC) are added to TEL to avoid lead deposits.
2. Tetra-methyl lead (TML).