30-04-2020, 08:17 AM
Many years ago I provided an article for a car club mag. Inflicting it on the Seven Forum will help amortise the effort.
Believe It Or Not (But All True)
Gleaned from the many dull automotive technical texts I have waded through over the years, some typical facts may interest.
Temperatures
1) Oil temperature in a big end is 30 deg C higher than sump temp.
2) With an iron cylinder head, combustion chamber surface temp is as much as 60 deg C hotter than with an alloy head. (Why my Minx pings on 8.3:1 c.r? Alloy permits one ratio of comp. increase.)
3) Flat out, piston crown temperature can reach 320 deg C. Then weak.
4) About 2/3 of the heat entering the piston crown is transferred away through the rings alone. (All traversing the cyl oil film!)
5) Exhaust valves often operate at 600 deg C (dark red), increasing at very high outputs to 750 deg C (red!). Plug electrode similar.
6) Comb. chamber gas attains about 2,600 deg C. Cast iron melts 1200 deg C
7) Temperature inside the spark momentarily reaches 60,000 deg C!
Pressures
8) Combustion chamber pressure in p.s.i. peaks at about 100x C.R. (Which is why Javelin engine thud gets even worse at 9:1!)
Under heavy pinging, the pressure increases about 20%.
9) When pinging, the spot pressure in the exploding gas can reach 2,700 p.s.i. accompanied by sonic shock waves. Hence the rattle!
10) Spot pressure in a plain crankshaft bearing may be 20 tons p.s.i.
11) Spot pressure in a rolling bearing may be 200 t.p.s.i.
Thicknesses
12) Crankshaft bearings are designed to operate with a minimum oil film of .8/10,000 of an inch. (cf thin hair 2/1,000 inch).
13) Cylinder wall oil thickness for the top ring is usually about 1 to 2/10,000 inch over most of the travel, dropping to .4/10,000 or less at the very top.
14) When oil films diminish below .4/10,000 inch metal-metal contact occurs, with associated wear.
Surprising
15) The top ring spends half its time in contact with the top face of the ring groove. (Where considerable wear occurs.)
16) A thin layer of cool unburned gas remains adjacent to the chamber and cylinder walls throughout. This prevents the engine melting! (An exception is when destroyed by condition 9!)
17) Under many conditions of operation, fuel travels along the inlet manifold partly as a river of liquid.
18) Pressure waves in ex/intake pipework travel at speed of sound.
19) Some high perf. engines acheive greater than 100% cyl. fill.
Believe It Or Not (But All True)
Gleaned from the many dull automotive technical texts I have waded through over the years, some typical facts may interest.
Temperatures
1) Oil temperature in a big end is 30 deg C higher than sump temp.
2) With an iron cylinder head, combustion chamber surface temp is as much as 60 deg C hotter than with an alloy head. (Why my Minx pings on 8.3:1 c.r? Alloy permits one ratio of comp. increase.)
3) Flat out, piston crown temperature can reach 320 deg C. Then weak.
4) About 2/3 of the heat entering the piston crown is transferred away through the rings alone. (All traversing the cyl oil film!)
5) Exhaust valves often operate at 600 deg C (dark red), increasing at very high outputs to 750 deg C (red!). Plug electrode similar.
6) Comb. chamber gas attains about 2,600 deg C. Cast iron melts 1200 deg C
7) Temperature inside the spark momentarily reaches 60,000 deg C!
Pressures
8) Combustion chamber pressure in p.s.i. peaks at about 100x C.R. (Which is why Javelin engine thud gets even worse at 9:1!)
Under heavy pinging, the pressure increases about 20%.
9) When pinging, the spot pressure in the exploding gas can reach 2,700 p.s.i. accompanied by sonic shock waves. Hence the rattle!
10) Spot pressure in a plain crankshaft bearing may be 20 tons p.s.i.
11) Spot pressure in a rolling bearing may be 200 t.p.s.i.
Thicknesses
12) Crankshaft bearings are designed to operate with a minimum oil film of .8/10,000 of an inch. (cf thin hair 2/1,000 inch).
13) Cylinder wall oil thickness for the top ring is usually about 1 to 2/10,000 inch over most of the travel, dropping to .4/10,000 or less at the very top.
14) When oil films diminish below .4/10,000 inch metal-metal contact occurs, with associated wear.
Surprising
15) The top ring spends half its time in contact with the top face of the ring groove. (Where considerable wear occurs.)
16) A thin layer of cool unburned gas remains adjacent to the chamber and cylinder walls throughout. This prevents the engine melting! (An exception is when destroyed by condition 9!)
17) Under many conditions of operation, fuel travels along the inlet manifold partly as a river of liquid.
18) Pressure waves in ex/intake pipework travel at speed of sound.
19) Some high perf. engines acheive greater than 100% cyl. fill.
