Re: Is it necessary to Add Lead to the gas?

Posted by Tom Fleming on November 04, 2011 at 01:33:01 from (206.193.250.146):

In Reply to: Is it necessary to Add Lead to the gas? posted by Livin the Dream on November 02, 2011 at 07:24:04:

Ken, interesting information, and I have seen some of those studies myself. Low RPM, low compression engines are definately less prone to valve seat errosion. My point still is that TEL was NOT added to gasoline to reduce valve erosion. The fact that it is an observed by-product of lead being in the fuel is a fair statement. however, with the addition of lead scavengers designed to "burn off" lead, I would question the residual effect of any lead in the gasoline. Lead oxide, which is a by-product of combustion is fairly lubricative as a compound but causes vavle failure due to deposit buildup. Lead bromide/chloride, which is the by-product of combustion in the presence of typically used lead scavengers, not so lubricative and exits with the exhaust gases. Essentially, a "chicken or the egg" debate.

Here is an excerpt from a combustion analysis:

A feature of TEL is the weakness of its four C–Pb bonds. At the temperatures found in internal combustion engines (CH3CH2)4Pb decomposes completely into lead and lead oxides and combustible, short-lived ethyl radicals. Lead and lead oxide scavenge radical intermediates in combustion reactions. This prevents ignition of unburnt fuel during the engine's exhaust stroke. Lead itself is the reactive antiknock agent, and TEL serves as a gasoline-soluble lead carrier. When (CH3CH2)4Pb burns, it produces not only carbon dioxide and water, but also lead:

(CH3CH2)4Pb + 13 O2 → 8 CO2 + 10 H2O + Pb

This lead further oxidizes to give lead(II) oxide:

2 Pb + O2 → 2 PbO

The Pb and PbO would quickly over-accumulate and destroy an engine. For this reason, the lead scavengers 1,2-dibromoethane and 1,2-dichloroethane are used in conjunction with TEL—these agents form volatile lead(II) bromide and lead(II) chloride, respectively, which are flushed from the engine and into the air.

Hardened valve seats, whether inserts (Stellite) or induction hardened seats, were recognized as necessary on high performance, high stress engines, and were a design point WAY before lead was removed from the gasoline.

Without all the chemisty, metalurgy, and observed physical behavior of engine valve components, the simple answer was provided very nicely and cleary by 504 in his post:

NO. :wink:

Replies:

• Re: Is it necessary to Add Lead to the gas? Indiana Ken 16:58:26 11/04/11 (0)

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