The development of crankcase ventilation systems with very high separation efficiency, precise pressure regulation, and an optimal service life is among our core skills and one of the central services of UT99.
FUNDAMENTALS OF CRANKCASE VENTILATION
When an engine is running, an oil mist forms in the crankcase. This mist has to be separated before it enters the atmosphere or the engine intake tract. Crankcase ventilation systems are a basic feature of internal combustion engines. Their purpose is to separate the oil mist and return it to the oil pan. They therefore play a significant role in reducing oil consumption and particle emissions, and thus contribute towards achieving compliance with the EU, EPA (e.g., Tier 4), and IMO threshold values for PM emissions. Such systems also regulate the pressure in the crankcase to prevent leaks and reduce gasket wear. This is of vital importance when using toxic fuels such as ammonia or methanol.
CRANKCASE VENTILATION: CLOSED (CCV) VS. OPEN (OCV)
Closed crankcase ventilation (CCV) systems, where crankcase gases are returned to the intake manifold, are increasingly being used compared to open systems (OCV). This is particularly true of engines that run on gaseous fuels, as they not only further reduce harmful emissions, but also increase energy efficiency by feeding any unburned fuel back into the combustion chamber. Systems such as these demand extremely high separation rates of > 99.5% (by mass) in order to avoid contamination in the intake tract and to ensure reliable operation of the turbocharger.
AEROSOL SOURCES
Aerosols always consist of a continuous gas phase and a dispersed phase (particles) of liquid and/or solids. Gases leak into the crankcase through piston rings, turbocharger shafts, and valve stems. These gas flows are also referred to as blow-by. They consist of a mixture of intake air, exhaust gases, and fuel, which is saturated with engine oil vapor in the crankcase. Particles form in the crankcase either through thermal processes (condensation) or mechanical processes (e.g., atomization). These particles consist almost exclusively of engine oil. In addition, soot, ash, and fuel can enter the crankcase. Oil vapors form at hot spots, e.g., on pistons or bearings. This oil vapor condenses in colder parts of the crankcase, creating new droplets, increasing the size of existing ones, or moistening macroscopic surfaces (e.g., walls). Particles can form mechanically at the piston rings, cooling nozzles, and moving engine parts (e.g., shafts). Due to the multitude of widely differing aerosol sources and their two very different generation mechanisms (thermal or mechanical), the crankcase of internal combustion engines contains extremely widely distributed aerosols that range in size from less than 10 nm in diameter to well over 100 µm.
REQUIREMENTS
The crankcase ventilation system has to fulfill two main tasks:
1. Separate the blow-by aerosols
- Ideal: total degree of separation (mass) > 99.5%
2. Regulate the pressure in the crankcase
- Ideal for numerous applications: vacuum of approx. -2.5 mbar
Sensors can also be integrated into the ventilation system to obtain valuable information about the operating status of the engine and the crankcase ventilation system. The most suitable sensors are those that detect the blow-by volume flow and the differential pressure across the filter.
Other important requirements for crankcase ventilation components are:
Compact dimensions
Chemical resistant (especially when using alternative fuels such as ammonia)
Temperature resistant
Vibration resistant
High gas tightness
Longevity (filter change interval > 4000 hrs.)
ATEX for certain applications
CRANKCASE VENTILATION FOR H2 ENGINES
Hydrogen-powered engines can create an atmosphere in the crankcase that exceeds the lower explosion limit of 4% by volume H2. Adjustments to the crankcase ventilation system are therefore recommended. An active ventilation system with a blower can flush the crankcase with filtered air. Components that conform to ATEX can also further reduce the risk of an explosion. Another challenge lies in the fact that burning hydrogen generates substantial amounts of water that have to be held in the gas phase through temperature management. Otherwise oil quality can suffer and emulsions may form that could block the filter.
CRANKCASE VENTILATION FOR AMMONIA AND METHANOL ENGINES
Engines running on ammonia or methanol can generate a highly toxic atmosphere in the crankcase. It is therefore advisable to modify the crankcase ventilation system. An active ventilation system with a blower creates a vacuum in the crankcase under all operating conditions, effectively preventing the escape of harmful gases. As ammonia can cause corrosion, it can sometimes be necessary to feed the crankcase gases to the exhaust gas system upstream of the SCR. The high pressure differences that exist will then need to be overcome. Depending on the engine concept, explosive mixtures may form in the crankcase. The concentration of these mixtures can be minimized by diluting them with conditioned air. Components that conform to ATEX can also further reduce the risk of an explosion. Another challenge lies in the fact that burning ammonia and methanol generates substantial amounts of water that have to be held in the gas phase through temperature management. At low temperatures, methanol can condense in the crankcase ventilation system. An enrichment of the condensate in the oil must be avoided to prevent the oil quality from deteriorating and the formation of emulsions, which could block the oil mist separator.
METHANE SLIP
The greenhouse gas potential of methane over a period of 100 years is around 28 times higher than that of CO₂. It is therefore of high importance that the methane emissions from internal combustion engines are reduced to a minimum. The proportion that open crankcase ventilation systems contribute to these emissions varies between 20% and 40% depending on the engine and its operating point. The most effective way of reducing this figure is to use closed ventilation (CCV) systems. These systems feed any unburned methane into the engine intake tract, where it is made available for combustion. Unburned methane can then be completely broken down in an exhaust treatment system.
Did you know?
Engines not equipped with oil mist filters have high levels of oil consumption.
Many legal limit values apply to the sum of crankcase and exhaust emissions.
The main tasks of crankcase ventilation systems are particle separation and pressure regulation in the crankcase.
The ideal pressure range in the crankcase depends on the application.