Managing Engine Blow-by with Crankcase Ventilation Systems

Last Updated On: 8/14/2023

By: Jason Cox




This article discusses engine blow-by, the issues blow-by causes, and the use of Crankcase Ventilation Systems to manage engine blow-by. We explain the different types of crankcase ventilation systems on the market and the benefits of each type. The engines discussed here are categorized as Reciprocating Internal Combustion Engines (RICE) and include spark Ignition (SI Engine) or compression Ignition (CI Engine) configurations. Stationary engines are utilized for power generation (ex. standby, peaking/shaving, prime power) and mechanical drive. (ex. gas compressors and pumps). Engines are also used in marine propulsion, onboard power, and locomotive installations.


What is Blow-by?

Blow-by is created when the air-fuel mixture and combustion gases leak past an engine’s piston rings. The pressurized air-fuel mixture and combustion gases leak into the engine's crankcase through small gaps between the rings and cylinder walls. The resulting mixture of lubrication oil mist and gases is called blow-by.


How is Blow-by Created? 

Most internal combustion engines use pistons, valves, and shafts to convert energy from controlled explosions into mechanical power. Pistons are the heart and soul of an engine. They move gases through the engine and harness energy created during the combustion/power stroke. Within the engine, pistons are connected to a rotating crankshaft and move in a linear direction within a fixed hollow cylinder. The crankshaft takes the linear motion of the pistons and converts it to a rotational motion which can be used to drive electric motors on generator sets, compressors, and other rotational equipment. The area of the engine in which the crankshaft resides is called the crankcase.  
When a piston completes its movement from the bottom of the cylinder to the top or the top of the cylinder to the bottom, the movement is called a stroke. When an engine is referred to as two-stroke or four-stroke, this indicates the number of strokes necessary to complete a combustion cycle. We will focus on the four-stroke type for this article and the four strokes that occur in this order:  Intake, Compression, Power, and Exhaust. Crankcase blow-by is generated during the compression and the power strokes.





Generally, new engines will have lower levels of blow-by when compared with older worn engines. As an engine operates, internal components within the combustion chamber begin to wear which causes gaps between the cylinder walls and piston rings to increase. This wear and tear allows more blow-by to leak past the piston rings into the engine crankcase. A good rule of thumb is to expect twice as much blow-by from a “worn” engine than a “new” engine.  




How Does Excessive Blow-by Harm an Engine?  

Engine blow-by must be vented from the crankcase to prevent several issues. Common issues include:


●    Excessive crankcase pressure - Elevated pressure in the engine’s crankcase can result in oil leaks through the engine seals which contributes to oil loss. 

●    Increased oil consumption - When blow-by contains high levels of oil mist that is vented to the atmosphere and not recovered, the engine’s lubrication system effectiveness can decline due to excessive oil consumption.

●    Decreased engine performance - When blow-by is routed back through the engine’s intake (closed crankcase). Oil and other contaminants can coat the internals of an engine’s components such as turbochargers and aftercoolers which can significantly decrease efficiency and performance.


What is Crankcase Ventilation? 

Crankcase Ventilation is the process of venting or removing blow-by from an engine’s crankcase to prevent excessive pressure build-up within the engine. Blow-by gases are mixed with oil mist and other contaminants that can harm an engine’s internal components and contaminate the environment. A high-efficiency crankcase ventilation filter is needed to clean the vented gases before returning to the engine’s intake or discharging to the environment. 


What are the Types of Crankcase Ventilation Systems? 

Depending on installation and emissions requirements, blow-by will be vented using two types of systems:   Open Crankcase Ventilation (OCV) and Closed Crankcase Ventilation (CCV).


OCV systems are applied when the crankcase blow-by exhausts to the atmosphere. An OCV system can be a simple low efficiency, low back pressure, wire mesh breather, or include a high efficiency coalescing element designed to capture large quantities of oil mist. The most effective OCV systems integrate a high-efficiency coalescing filter with a vacuum source and a crankcase pressure regulation mechanism. An advantage to using open crankcase ventilation systems is that the possibility of contaminant and oil build-up within the turbo and aftercoolers is minimized. This is especially important in landfill gas, biogas, syngas, and other installation sites where gas quality can be an issue (Solberg SME and ACVB).


CCV Ventilation Systems are applied when crankcase blow-by is routed back to the engine’s intake. In most scenarios, it will be routed upstream of the turbo (compressor wheel) and downstream of the engine air cleaner. Some will be routed into the engine exhaust. As environmental regulations are becoming more stringent, the use of closed crankcase ventilation (CCV) systems is increasing. Venting blow-by back through the engine’s intake path allows operators to monitor total emissions through the engine’s exhaust and eliminate an emissions source. Closed crankcase ventilation systems are suitable for many installation types particularly when the CCV has integrated pressure regulation technology (Solberg ACV).


Both system types can effectively manage crankcase pressure and meet environmental regulations. Refer to chart 1.1 below for additional details.


What are the Benefits of a Crankcase Ventilation System?

A well-designed and properly sized crankcase ventilation system significantly helps maintain an engine’s reliability and lowers maintenance costs over time. It will reduce engine oil consumption and improve engine efficiency and performance. It does this by regulating crankcase pressure within a specified range and by capturing oil entrained in the blow-by gases.

Regulating Crankcase Pressure 

Crankcase pressure can be managed by using the engine's intake as a vacuum source (CCV) or an external vacuum source such as a regenerative blower (OCV). In either scenario, the vacuum level must be regulated to ensure the crankcase pressure is maintained within a specified range. This is normally accomplished using manual valves, automatic valves, or variable speed drives. For CCV systems, the advancement is to use automatic vacuum regulation valves such as the type found on Solberg’s ACV and ACVB series product lines.   For OCV systems, manual valve control is most common, however other technologies such as recirculation systems (SME-R) and automatic mechanical control (Solberg ACVB) are gaining traction in a broad range of engine applications. Specifications for engine crankcase suction or pressure typically fall within the range of (-3) to (+2)” W.C., (-7.5) to (+5) mbar or (-0.75) to (0.5) kpa. Engine OEM specifications vary by engine make and model and it is best to consult with the OEM Operations Manual for the ideal crankcase operating pressure range for a specific engine.

Lowering Oil Consumption

The crankcase filter cleans the vented blow-by gases to make sure that they are contaminant-free before discharging to the environment or returning to the engine’s intake. Oil mist is the primary concern when venting blow-by gases. The filter’s function is to capture and coalesce oil mist entrained within the blow-by and return it to the engine or a waste oil sump. When returning the oil to the engine’s crankcase, oil consumption due to crankcase venting can be significantly reduced.

Improving Engine Efficiency 

Both Closed crankcase ventilation (CCV) and open crankcase ventilation (OCV) system types remove contaminants and pollution from crankcase emissions. The filter’s efficiency is especially critical for any CCV system application. High-efficiency coalescing filters are very effective in reducing the build-up on turbos, aftercoolers, and other internal components. Some particulate and oil mist does make it through the filters. Eventually, contaminants will build up which could potentially affect the turbocharger surfaces and reduce operating efficiency. Therefore, it is best to select the highest efficiency filters possible when routing blow-by back through an engine’s intake.  

(High-efficiency filtration typically ranges from 99% to 99.97% efficiency at 0.3um)

Protecting the Surrounding Environment 

Crankcase ventilation systems with high-efficiency filters keep oil mist, smoke, odors, and other particulates from entering the surrounding environment. When open crankcase ventilation (OCV) systems vent untreated blow-by into the atmosphere, oil mist will accumulate in buildings, and on surrounding equipment including the engine.  As oil accumulates on surfaces it becomes a slipping hazard and potentially a fire hazard as well. Oil mist accumulation in poorly ventilated spaces can cause respiratory issues and eye irritation for plant personnel. Additionally, engine seal leaks caused by excess crankcase pressure can create slipping hazards for plant operators.

Meeting Environmental Regulations 

Reducing or eliminating crankcase blow-by emissions may be required by national or regional agencies (EPA, IMO, etc). Specific requirements are typically dependent on the fuel type, stationary or marine installation, and the duty (continuous or standby).  Even if your engine is not governed by specific regulations, it is best to promote environmental responsibility and safety by capturing vented oily blow-by emissions.


A Complete System.  Beyond Just A “Crankcase Filter”

Crankcase ventilation requirements are unique to each engine model and installation site. Engines are becoming more efficient and more complex every year.  As a result, the “one size fits all” products may not be the best solution to control emissions and promote optimal engine performance.  For modern, high efficiency and low emissions engines, most will require high-efficiency filtration while contributing minimal back pressure to the engine crankcase. A fit-for-purpose open or closed crankcase ventilation system is necessary to achieve emissions targets and site-specific requirements.  A complete crankcase system can include a specific piping configuration, mounting location, drain line type and location, waste oil consoles, exhaust location as well as insulation jackets for the filters and piping.  





Installing the ideal system for a specific engine, plant, or marine vessel will help to promote engine performance, safety, and environmental compliance while improving reliability and lowering the overall cost of ownership.  If you have any questions regarding crankcase ventilation systems, please contact Solberg Manufacturing. 


Chart 1.1




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