Abstract
KEYWORDS
air pollution, diesel engines, blow-by gas, crankcase venting system, oil separators.
ABSTRACT
The paper presents some considerations regarding generation and abatement techniques of air pollutants (CO, CmHn, NOx, particulates) from exhaust gas and oil particles taken over from oil sump. The blow–by gas drives in ascendent movement fine oil particles from oil sump thus producing the elimination in the atmosphere of some oil mass contributing to oil consumption increase. In order to reduce the impact of that source of emissions there is a need of separation and retaining of oil particles from blow–by gas. Discussion is made on combustion chamber sealing by piston –ring system appreciating it as normal if the gas pressure after last piston ring is 3-4 % of cylinder intake pressure and the blow–by gas flow 0,2 – 1 % from the air intake flow. The crankcase venting systems ( natural and pressurized venting system ) seemed to be compulsory to the passenger cars, but not yet to heavy duty diesel engines to which they may generate problems : at high temperatures the compressor rotor will be covered with carbon residues from oil, the air cooler with oil residues will have higher pressure drops and oil from recirculated engine air intake will increase the particulate matter existing in exhaust gas.
It was estimated that heavy duty commercial vehicles eliminate into atmosphere on the life span around 100 oil litres in a breathable state or in other figures to 2÷15 g/h oil loss or 2÷12% from oil consumption . These values can be higher if the venting point is not positioned correctly. That is why some techniques must be applied and experimented. For a series of Romanian manufactured diesel engines there were determined at Road Vehicle Institute (INAR) the blow–by gas flows necessary to the dimensioning of oil separators detailing gas dynamics limitations. Finally there were designed several oil separators and venting system prototypes considerably limiting the oil mass entrained in the atmosphere.