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The crankcase of combustion engines is an undesirable source of oil vapor and oily aerosols. The roles of nucleation and growth by vapor condensation in their formation (with and without preexistin...

Crankcase ventilation systems are coming into new focus due to safety concerns associated with alternative fuels such as ammonia and hydrogen. In addition, innovation is being driven by increasingly stringent legislation that plays an important role in limiting crankcase emissions. This study characterizes aerosol separation and pressure control of a modern crankcase ventilation system, which is referred to as “smart” due to enabling monitoring, diagnostics, and predictive maintenance. Experiments were conducted on custom-built and commercial test rigs that mimic the physical conditions to which crankcase ventilation systems are subjected. The main findings were that the pressure drop of the filter media followed the profile described by the “jump-and-channel model”, also indicating the presence of an oil film. However, such an oil film was not detected on the full-size element, which had a positive effect on the pressure drop. Excellent separation efficiencies around 99.9% were achieved for all flow rates and filter conditions. In addition, re-entrainment of oil was not detected. The electronic pressure regulator (EPR) was found to accurately (± 1 mbar) adjust the crankcase pressure to the required level. Moreover, the fully open EPR featured a low differential pressure of about 1 mbar, which effectively reduces crankcase peak pressure during engine startup. These features exceed those of conventional pressure control valves. In addition, only the electronic regulator enables “smart” features.

Particulate emissions from diesel engines are a matter of public concern and continued industrial development. For an internal combustion engine, particles may originate either from the after treatment box or from the crankcase ventilation system. This paper quantifies and discusses particle sources within the crankcase ventilation system of a medium-duty 4-cylinder and a heavy-duty 6-cylinder engine and their dependence on the engine oil parameters viscosity (expressed as Noack number) and HTHS volatility. Crankcase aerosol spectra were measured by an optical particle counter in the size range of 0.3–5 µm. For a few cases data of filter samples downstream the separator unit are discussed for the total blow-by aerosol. Engines were found to behave very similarly with regard to changes in either oil parameter, with volatility generally being the far stronger factor of influence. Total particle mass concentration increased by a factor of up to 5 for a rise in Noack volatility of about 13–25%. The mass concentration downstream of the separator also increases with oil volatility. A variation of HTHS viscosity from 3.5 to 2.6 mPas generated a marginal change in aerosol output by a factor of about 1.2. However, and unexpectedly, the most viscose oil generated the relatively highest particle mass concentrations for both engines.

Crankcase aerosol contributes to the particulate matter (PM) emissions of combustion engines equipped with an open crankcase ventilation system. In case of closed crankcase ventilation, the aerosol forms deposits that diminish engine efficiency, performance, and reliability. Such issues are best avoided by highly efficient filters combined with in-engine reduction strategies based on a quantitative understanding of aerosol sources and formation mechanisms in a crankcase environment. This paper reports key findings from a study of aerosol spectra in the range of 0.01 μm to 10 μm obtained from a 1.3-L single-cylinder engine under well-defined conditions. Supermicron particles were formed mainly by cooling jet break-up when the piston was positioned in TDC, while at BDC aerosol generation decreased by about 90 % because the oil jet was short and thus stable. Motoring the engine yielded an additional peak around 0.7 μm. It is associated with oil atomization at the piston rings and increased strongly with cylinder peak pressure. No significant contribution of the bearings could be identified at peak pressures below 116 bar. Engine speed had only a minor effect on aerosol properties. Operating the engine in fired mode increased the submicron aerosol concentration substantially, presumably because high(er) peak pressures boost aerosol generation at the piston rings, and because additional particles may have formed from recondensing oil vapor generated at hotspots. Soot or ash aerosols could not be identified in the crankcase aerosol, because they may have been integrated into the bulk oil.

Understanding how engine design and operation affect blow-by aerosol characteristics is key to reducing the emission of particulate matter (PM) via the crankcase ventilation system. To this end, representative aerosol data from four different diesel engines are compared on the basis of brake mean effective pressure (BMEP) and engine speed. The data were obtained from comparable sampling positions, using the same sampling system and optical particle counter. The discussion is based on the narrow particle size range of 0.4–1.3 µm, chosen for its significance with regard to blow-by aerosol sources, as well as for the challenges it poses for separation systems. Key findings include particle size distributions (PSD) of virtually identical shape, indicating that these engines share the same aerosol sources and underlying generation mechanisms. However, absolute concentrations differed by a factor of about six, presumably due to differences in engine design, which in turn affect key parameters such as temperature, pressure and flow rates. At BMEPs ≤ 10 bar all engines exhibited similarly low aerosol concentrations. With increasing BMEP the concentration rose exponentially. The engine with the smallest rise and the lowest total concentration featured an aluminum alloy piston, the smallest displacement, the lowest peak BMEP as well as the lowest maximum oil temperature. At maximum torque the aerosol concentration scaled fairly linearly with engine displacement. Increasing the engine speed had a minor impact on aerosol concentrations but affected blow-by flows, hence leading to a rise of aerosol mass flows. Within the limits of this comparative measurement studies, three generation mechanisms are provided for blow-by aerosols.

The particle size distribution (PSD) of submicron exhaust engine-out soot, is typically determined using a method based on the electrical mobility is used. This measurement procedure is subjected to uncertainty mainly due to inaccurate dilution of the sampled aerosol, unknown flow conditions at the probe inlet and the limited measurement accuracy of the device itself. In order to determine the measurement uncertainty, two different aerosol spectrometers, a TSI EEPS 3090 and a Cambustion DMS500 were installed and operated simultaneously at a single-cylinder heavy-duty diesel engine at the Institute of Internal Combustion Engines of the Karlsruhe Institute of Technology (KIT).The engine was operated at various operating points to evaluate the ability of the spectrometers to correctly determine the PSD and the total particle number concentration (TPNC) at different boundary conditions. Variations of the position and geometry of the probe systems were performed, to evaluate the influence of the flow conditions at the probe inlet. The dilution systems of both measuring devices were verified by varying the dilution factor in three steps. Both particle sizers show good agreement in the TPNC. It could be confirmed that the probe geometry and its positioning had a negligible effect on the properties of the exhaust gas sample. A slight shift in PSD between the EEPS and the DMS was observed at the engine test bed. For a detailed evaluation, a device comparison with monodisperse polystyrene (PSL) particles with a SMPS as reference was performed at the Institute of Mechanical Process Engineering and Mechanics (KIT).

Particle size distributions (PSDs) of engine blow-by aerosol are commonly obtained with an optical particle counter (OPC), but representative measurements are challenging due to high number concentrations, elevated temperatures, presence of saturated vapor, as well as unsteady flow conditions. A comprehensive study of blow-by aerosol sampling/conditioning and OPC performance in such an environment was therefore conducted, based on a commercial OPC (Palas Promo 2000). Single (1:9) and double-stage (1:80) sampling/dilution/conditioning systems were devised and their transfer functions characterized in the OPC sensor range of 0.3–17 μm. With (mostly inertial) particle losses >90% at 10 μm, correcting for them was crucial for reliable PSD measurements. The effect of saturated oil vapor on droplet growth during cool-down and dilution of the sample flow was investigated between 80 and 120 °C, based on actual vapor concentration data. Without dilution, droplet growth became significant above 100 °C while diluting 1:20 with 20 °C air suppressed growth. Tests of over-all sampling and dilution strategy with engine blow-by aerosol gave excellent reproducibility and good agreement (after loss corrections) with reference data regarding PSD in the 0.3–10 μm range as well as total mass. The actual engine blow-by PSD was significantly broader though, exceeding the OPC range on both ends. Number-to-mass conversion of OPC data under-reported total mass by 10%–20% (depending on sensor range) compared to weighed filter samples, provided OPC contamination with oil deposits was avoided. A re-calibration procedure is proposed to deal adequately also with pressure pulsations resulting from engine operation.