MEASUREMENT OF DIESEL BLOW-BY GASES
MEASUREMENT OF DIESEL BLOW-BY GASES
(OP)
We have been asked by a client to add some instrumentation to an engine test rig to measure 'crankcase blow-by' in order to assess cylinder wear, ring condition etc.
The client has only asked for a measurement of pressure, but in a vented crankcase this is likely to be so near atmospheric as to be immeasurable. I believe that what is needed is a measure of volumetric flow, ie the rate at which gas leaks past the pistons.
I have no idea what is a reasonable figure for a good engine, or what you might expect from a seriously worn one. The manufacturers seem to think zero is a good figure - I'm sure it is, but what is acceptable?
The engine is a turbocharged intercooled 20 litre V-12 diesel producing 900kW @ 2300 rpm.
Any guidance? Or experience of this type of testing?
The client has only asked for a measurement of pressure, but in a vented crankcase this is likely to be so near atmospheric as to be immeasurable. I believe that what is needed is a measure of volumetric flow, ie the rate at which gas leaks past the pistons.
I have no idea what is a reasonable figure for a good engine, or what you might expect from a seriously worn one. The manufacturers seem to think zero is a good figure - I'm sure it is, but what is acceptable?
The engine is a turbocharged intercooled 20 litre V-12 diesel producing 900kW @ 2300 rpm.
Any guidance? Or experience of this type of testing?





RE: MEASUREMENT OF DIESEL BLOW-BY GASES
RE: MEASUREMENT OF DIESEL BLOW-BY GASES
Many thanks for these useful numbers. I now have an approximate range to select an airflow meter. Point taken on temperature compensation - we can easily do this.
I still don't think that crankcase pressure tells us much unless the breather(s) are calibrated. A restrictive breather will give a substantial pressure but a large diameter hose will maintain the crankcase pretty much at atmospheric pressure.
I am not familiar with a turbo drain tube - does this normally vent significant quantities of compressed air into the crankcase? Why? Is this air which gets into the turbo lube system when turbo bearings are worn?
RE: MEASUREMENT OF DIESEL BLOW-BY GASES
Many manufacturers, including Cummins, use crankcase pressure as the gage for TBO's.. A manometer is tycally the tool of choice..........
Tony
Tony Athens
http://www.sbmar.com
RE: MEASUREMENT OF DIESEL BLOW-BY GASES