10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Influence of Design Parameters and Operating Conditions on the Aerosol Produced by a Laskin Nozzle
BENOIT SAGOT, Louise Chazalon, Lyes Ait Ali Yahia, ESTACA
Abstract Number: 960 Working Group: Aerosol Physics
Abstract Oil separators are used in the automotive industry for the separation of oil mist from blow-by gases in internal combustion engines. These so-called “blow-by gases” result from leakages between the combustion chamber and the crankcase. These gases flow through the crankcase, which contains lubricating oil and the resulting oil mist, has to be cleaned up, for pollution control, oil consumption reduction and also to avoid turbo charger oil coking. To compare oil mist separators performances in laboratory, it is necessary to reproduce the engine operating conditions such as temperature and flow rates but also in terms of oil droplets distribution, and we developed such a laboratory bench.
A new generation of SI engine is currently under development, and new trends in engine design are a reduction of the engine size, an increase of the engine temperature, and a reduction of the oil viscosity. The targets are reduction of friction, increase of the overall efficiency, together with a reduction of the pollutant emissions. However, we observed that these changes in the design produced a strong increase of the overall oil mass concentration of blowby gases, which has been multiplied by a factor over 10. At the same time, the mean mass diameter of the aerosol distribution has been strongly reduced. We attribute this modification of the aerosol distribution to the reduction of the oil viscosity, and to higher cylinder pressure. Classical separation systems used in SI engines are based on impactors or cyclones. But to maintain the separation efficiency for the submicronic fraction of oil mists, car manufacturer are now using new systems that include filtration media, with high collection efficiencies and low pressure drop. For filter manufacturers, there is a new challenge: they test these filters on laboratory benches, with gravimetric measurements based on Andersen cascade impactors, and the downstream measurement time is very long (hours), since classical Laskin generators are not capable of producing a high concentration of the submicronic fraction of the aerosol. Therefore, for the submicronic fraction, there is a high uncertainty on the collection efficiency, even for long measurement times that also impose a high stability of the aerosol generation.
The aim of this study is to investigate the capacity of the Laskin nozzle to generate highly loaded oil mist with a low mean mass diameter, with a distribution equivalent to what is currently measured in under development SI engines. The first point is to quantify the impact of operating conditions such as oil temperature and gas flow rate in the Laskin nozzle, on the produced aerosol, in a wider range than what can be achieved with commercial devices such as the Palas PLG 2010.
We observed that for a given Laskin nozzle, the oil temperature has a strong impact of the overall oil concentration, with a limited variation of the mean mass diameter. These results are correlated to the reduction of the oil viscosity. The oil temperature was varied in the range 100°C to 200°C, and we observed a thermal degradation of the oil (SAE 0W30) for temperature higher than 160°C.
The flow rate in the Laskin nozzle has a strong impact on both the overall oil concentration, and on the aerosol distribution. The increase of the flow rate first produces an increase of the overall oil concentration. Then, a dilution effect appears, and we observe a bell shape curve for this oil concentration. However, for the submicronic fraction of the aerosol which is our main concern, the amount of oil droplets produced keeps increasing, which produces a reduction of the mean mass diameter. The last point of this study concerns an investigation of the influence of the geometrical parameters of the nozzle on the produced aerosol: for a fixed gas flow, we tested five nozzles with diameters in the range 0,3 to 1 mm. Based on Andersen cascade impactor gravimetric testing, the influence of the gas nozzle diameter was characterized.
With this experimental study, we were able to produce an oil mist distribution close to what is measured on under development SI engines. We got a better understanding of the way a Laskin nozzle works, which will be helpful for further development of filtration systems.