WHY LEAD ANYWAY? You might be surprised to learn that the first petrol didn't have lead! That was up until the early 1920's. By then, the design of car engines had progressed to a more advanced state, and in a quest for greater performance, were running higher compression ratios (although they were still very low by today's standards). This created a problem with what is referred to as "pinging" (or "knocking"). This is a rattling-type sound that occurs particularly when the motor is under load (pulling hard, or accelerating). In simple terms, what happens is the fuel "explodes" rather than "burns". So engineers were looking for something to add to the petrol to slow down the "burning" process. Thomas Midgie is the person accredited with discovering the compound lead tetraethyl which, by raising the octane-rating, was able to slow down the combustion and eliminate this pinging effect. |
THE PROBLEM OF REMOVING THE LEAD There was another advantage to lead though; it had a kind of "lubricating" effect. As the fuel was burnt, the lead left deposits on internal components, in particular the valves and valve-seats. This created a kind of "cushion" that protected the valves and valve-seats from excessive wear. The diagram on the left shows a cutaway illustration of a typical over-head valve engine. (Earlier engines, referred to as "side-valve" design, had the valves located in the side of the engine-block, but the principle - and the problem - is the same). At normal running speeds, these valves open and close at an average of 20 to 40 times every second. Without the "cushioning" effect of lead, this constant pounding of the valve where it meets the cylinder-head (the valve-seat) would cause rapid wear, resulting in the valve burying itself deeper into the cylinder-head. This is called "Valve-Seat Recession", (or "VSR"). Fig. 2 is a close-up diagram of a valve that is seated normally. Fig. 3 is a close-up diagram of a valve that has suffered valve-seat recession. To overcome this problem, the engine design of new cars was modified to incorporate specially hardened valve-seats that would withstand this constant pounding, and not result in VSR. For older cars though, without these specially hardened valve-seats, VSR would be a real problem if they were to use the new Unleaded fuel. (It should be mentioned here that hardened valve-seats can be fitted to many older cars, but that involves dismantling the engine, and is a very costly operation). But when you realise that Lead Replacement Petrol, which we now have to use in older cars, is actually Unleaded Petrol with additives to replace the action of lead, then we have to wonder if these additives are doing the job of lead satisfactorily. The oil companies claim that the octane-rating of LRP is 96 - exactly the same as the old Super. But their assurances on it's effectiveness in preventing VSR have sometimes been less than totally reassuring! The other problem, of course, was that removing the lead- additive reduced the octane rating, and so "pinging" would again be evident. This could partly be overcome by modifying engine design to accommodate the lower octane fuel, but other additives had to be used to increase the octane rating. Some of the additives that have been used include benzene, toluene, xylene, dimethylbenzene, and mesitylene. HEALTH CONCERNS WITH UNLEADED PETROL Even before Unleaded petrol was introduced, there were people who were concerned over it's potential health problems. But wasn't Unleaded introduced so that we could fit catalytic converters that would filter out all these harmful emissions? Yes, but the problem was these catalytic converters don't work properly until they have reached a temperature of around 400 degrees. That means that until the car, and the exhaust system with it's catalytic converter, has driven some distance and properly warmed-up, the engine would be producing untreated emissions into the air. And, it was claimed, as some of these additives were declared to be carcinogenic, these emissions were more harmful than that of the old leaded petrol! As far back as 1983, a Dr. Watson, who was a scientific advisor to the committee for Energy Resources, expressed grave concerns about the proposed new fuel. He claimed that it was "so dangerous, and potentially lethal" that it should not be used in any car not fitted with a catalytic converter! Now, remembering that LRP, which we use in older cars, without a catalytic converter, is really Unleaded petrol, then it does indeed raise the question of what health problems there may be with using this fuel in older cars. |
Click on the old car again to go to the next section; to find out more about the PROBLEMS WITH LRP. Read about common problems reported, plus personal experience of people (including myself) who have been using LRP. Discover that all LRP is not the same! And there even more possible health problems! |
Click here to go back to Main Page |
THE PROBLEMS WITH REMOVING THE LEAD |
