Getting some lip on squish
Page 25
If you've noticed an error in this article please click here to report it so we can fix it.
WE AT the British Internal Combustion Engine Research Institute (BICERI) have read your article (CM, March 14, p 54) on the most interesting development of the squish lip, and would like to offer our comments.
First, you mention the lengthy interval between the initial announcement of the squish lip in 1974 and its practical application to commercial products. We believe that a paper presented to International Congress on Combustion Engines (CIMAC) in 1979 by Dr Adams states: "The problem associated with re-entrant bowl pistons, however, is their susceptibility to cracking in the throat region of the combustion bowl due to its high thermal and mechanical loadings".
The paper then proceeds to describe a three-year programme of research, both complex analytical work and intensive engine testing, aimed at gaining "basic knowledge of the failure mechanism in order to be able to extend piston life and finally to produce a solution to re-entrant bowl piston throat cracking".
This presumably explains why the squish lip has been introduced to the market in small engines of low load factor, and is only slowly working its way through the engine range.
Ft is also stated that in the USA "cetane number varies from 40 at the high end to a dubious 30 at the bottom". The most reliable source of information on this subject is the US Energy Technology Centre, which publishes an annual survey of .diesel fuel quality based on analyses of fuel samples collected countrywide on a systematic basis.
The most recent of these surveys (published December 1980) shows that, for a set of 200 fuel samples, the cetane number ranged from a maximum of 56 to a minimum of 37, against a specification minimum of 40.
We consider it most unlikely that, over the few months since this survey was made, cetane number could have fallen to the extent suggested by your published figures.
Indeed, if such catastrophic declines are happening, they must surely prejudice current interest in the automotive diesel engine in the USA.
W. TIPLER Consultant BICERI Slough, Berks