Internal combustion lead from

The deposits formed in internal combustion engines by high-octane petrols may be classed as ashes they consist of mixtures of lead oxides, bromides and sulphates derived from the anti-knock additives and, of course, exert their main corrosive effect on the parts operating at the highest temperature the exhaust valves and the sparking-plug electrodes. 

A major engineering textbook from 1998, which should contain just about everything one needs to know about Diesel emissions, is entitled Handbook of Air Pollution from Internal Combustion Engines with the subtitle Pollutant Formation and Control. The book is co-authored by a dozen of the world s leading experts on automotive emissions. It should be an excellent source of information on precisely how one might kill people with Diesel exhaust. But in the entire 550 page book, which is rather typical of all other hooks one can find on this subject, there was only one sentence relevant to our subject.65... 

Whether decarburization will be an issue for internal combustion engines burning H2 is difficult to predict from existing information. Low-alloy carbon steels begin to decarburize at temperatures around the operating temperature of exhaust valves, but exhaust valves and valve seats are made from high-alloy steels, austenitic alloys, and superalloys where the carbon is much more stable than low-alloy carbon steels. The hardenable martensitic valve stems of exhaust valves may experience decarburization over extended periods, and this would lead to accelerated wear because of the softened surface that results from decarburization. 

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