![]() Oil evaporation is characterized by the Noack volatility, defined as the percentage of oil mass loss during 60 min at 250 ☌. The oil formulation is furthermore critical in minimizing the consumption of engine oil, driven by oil transport to the combustion chamber as well as evaporation at elevated temperatures. A stable HTHS value needs to be maintained as long as possible, despite the accumulation of soot and unburned fuel, to maximize oil change intervals. A key parameter to that effect is the high-temperature high-shear (HTHS) viscosity of the oil, usually determined at a temperature of 150 ☌. ![]() Reduced inner friction contributes also to fuel savings and helps to reduce CO 2 emission. Its principal function is of course to lubricate, cool, and clean critical components during operation. Įngine oil is a major factor for vehicle performance. Both are most likely associated with re-condensation of engine oil vapor generated in the hottest regions of the crankcase. According to recent work on the sources of crankcase aerosol, the number size spectrum has two dominant peaks in that size range, one around 200 nm and one around 400 nm. The submicron part of the blow-by aerosol spectrum is, therefore, of most concern. State-of-the-art passive separators are generally capable of removing super-micron aerosol particles from the blow-by gas, but become much less efficient below about 1 µm. In either case, however, the additional burden of oily crankcase aerosol represents a problem: In a closed system the particles can cause critical engine components to deteriorate, while in an open system they contribute to the overall emission level included in the emission certification on the test bench or the PEMS measurement procedure on a vehicle. Both closed and open crankcase ventilation systems are in current use and have their respective advantages and disadvantages. After passing through a particle separator, the remaining, rather fine “blow-by” aerosol is either recirculated to the air intake or directly vented to the environment. The crankcase of combustion engines is a major source of aerosol particles, beside the combustion vented through the exhaust aftertreatment system. Furthermore, for the scheduled Euro VII emission legislation, the consortium for ultra-low vehicle emissions (CLOVE) proposes to reduce the lower particle size limit for number concentration measurements from 23 to 10 nm while retaining with the same limit of 6 × 10^11 for particles per kWh, which would require an overall reduction of about 70% in particle number concentration. These tests have also become mandatory under China VI-b regulations. Starting with Euro VI-e in 2021, these limits apply also to tests with a portable emission measurement system (PEMS). However, and unexpectedly, the most viscose oil generated the relatively highest particle mass concentrations for both engines.Įmission reduction in the automotive sector has often been driven by legislation, notably Euro VI, which in 2012 imposed particulate emission limits based on total number concentration. 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. The mass concentration downstream of the separator also increases with oil volatility. Total particle mass concentration increased by a factor of up to 5 for a rise in Noack volatility of about 13–25%. 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. For a few cases data of filter samples downstream the separator unit are discussed for the total blow-by aerosol. Crankcase aerosol spectra were measured by an optical particle counter in the size range of 0.3–5 µm. 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. ![]() For an internal combustion engine, particles may originate either from the after treatment box or from the crankcase ventilation system. Particulate emissions from diesel engines are a matter of public concern and continued industrial development. ![]()
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