Cylinder wall deposits

During normal engine operation carbonaceous deposits, derived from the fuel and lubricant, build up and reach quasi-stationary levels after a driving distance of about 10,000 km, and affect a number of aspects of engine operation. Kalghatgi [145,146] has extensively reviewed the subject and only a brief account of the effect on autoignition is given here. 

The most important effect of combustion chamber deposits is that they make the engine more knock-prone as they build up. This is quantified as an octane requirement increase (ORI), and it typically reaches 5-10 octane numbers. Several mechanisms probably play a part in the phenomenon. Principally these are volumetric, thermal and chemical. The volumetric effect is the increase in the compression ratio caused by the volume of the deposits. This has been estimated [147] to be responsible for only about 

This section outlines the general way in which the chemical reactions in the end gas can be modelled, when its temperature and pressure are 

Let [A] be the molar eoncentration of ehemieal speeies A, in reacting end gas, one mole of which occupies volume v. If the net volumetric chemical source term for moles of A is 5, then the eonservation equation for A in one mole of end gas is. 

The mole fraction of A, ([A]v), is unaffected by volume changes, only by the chemistry. It follows that 

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The wall film, abc, is considered first. It is continually deposited on the cylinder wall at point a with a uniform initial concentration, C, equal to that of the nip (assumption 1). The surface concentration immediately drops to the equihbrium value, C (assumption 2). The initial shear gradient in the film at point a quickly disappears and the surface layers will rotate with the barrel until absorbed and mixed by the nip at point c. It can be shown that over the range of... 

Nickel plating is widely used for a corrosion- and wear-resistant finish. Typical applications, with a thin top coat of electrodeposited chromium, are decorative trim for automotive and consumer products and office furniture. Nickel deposits are also used for nondecorative purposes for improved wear resistance, for example, on pistons, cylinder walls, ball studs, and so forth. 

New materials also emerged. Nylon, developed brilliantly by W. H. Carothers and his team of research workers for Du Pont as a fibre in the mid-1930s, was first used as a moulding material in 1941. Also in 1941 a patent taken out by Kinetic Chemical Inc. described how R. J. Plunkett had first discovered polytetrafluoroethylene. This happened when, on one occasion, it was found that on opening the valve of a supposedly full cylinder of the gas tetrafluoroethylene no gas issued out. On subsequently cutting up the cylinder it was found that a white solid, polytetrafluoroethylene (PTFE), had been deposited on the inner walls of the cylinder. The process was developed by Du Pont and, in 1943, a pilot plant to produce their product Teflon came on stream. 

The ACC is a stainless steel cylinder 3 in. in diameter and 1 ft long through which exhaust gases pass before they enter the muffler and tailpipe. The converter contains an extmded ceramic honeycomb stmcture with square pores 0.5 mm in diameter through which gases pass. The walls of these pores are coated with porous y-Al203 on which Pt, Pd, and Rh are deposited, along with several catalyst promoters such as cerium oxide. The residence time in the ACC is -0.05 sec, because the volume of gas that must be processed... 

Whenever new engines bum fuel, a certain amount of carbonaceous material builds up on the walls of the combustion chamber and the piston crown. These deposits act to increase the compression ratio and temperature of the cylinder environment. After about 10,000 miles, most vehicles accumulate enough deposit so that their... 

The tubular centrifuge, which is shown schematically in Figure 9.3a, incorporates a vertical, hollow cylinder with a diameter on the order of 10 cm, which rotates at between 15000 and 50000 rpm. A suspension is fed from the bottom of the cylinder, whereupon the particles, which are deposited on the inner wall of the cylinder under the influence of centrifugal force, are recovered manually in a batchwise manner. Meanwhile, the liquid flows upwards and is discharged continuously from the top of the tube. 

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