What causes air intake system contamination and combustion system carbon buildup?

There are several factors that contribute to the formation of carbon deposits in an engine’s combustion chamber. These factors are as follows;

  • Quality of fuel (not grade)
  • Extreme outside ambient temperature / Humidity
  • Re-circulated crankcases gases
  • Driving conditions
  • Optimized fuel and ignition efficiency

Each of the factors identified contribute to a less than optimal fuel burning process in an engine’s combustion chamber. Fuel, oil and miscellaneous other compounds are introduced into the engine’s combustion chamber via the air and fuel management system to produce energy to power a vehicle. In the more than 100 years since the gasoline reciprocating engine was designed and introduced as the main power source for a vehicle, it has never been designed to fully burn the fuel it uses. Over time new engine designs and more specifically improved fuel management systems and computerization have contributed to significant improvement air and fuel efficiency that enables a higher level of the potential energy available from the fuel to be utilized.

To better understand the formation of carbon deposits in an engine’s combustion chamber, it is best to understand how each of the factors individually contributes to the build-up of carbon and afterwards assess the impact on the build-up when two or more factors combined are present.

Quality of fuel

The refining process for crude oil to produce gasoline has changed over time and the crude oil being used varies from one oil field to another. Light, sweet or heavy crude are made up of the same key properties for producing gasoline, however the type and number of contaminants present in the fuel varies based on the type of refining process used. The higher the level of contaminants in the gasoline the greater the potential for developing carbon deposits in an engine’s combustion chamber.

 Extreme outside ambient temperature / Humidity

A modern day vehicle is designed to optimally perform in the moderate temperature range. Extended periods where the air temperature and the humidity decreases, the air density increases causing the air-fuel management system to deliver a richer air-fuel mixture, a mixture that cannot burn completely in the short time given for the burn/power process. As a result the excessive fuel runs down the cylinder walls and settles in the oil reservoir.

In an environment where the air temperature and humidity increases the air density decreases requiring the air-fuel management system to deliver a leaner air-fuel mixture. A lean fuel supply reduces the potential power output from the engine causing spark plug fouling which contributes to the build-up of carbon deposits in the combustion chamber.

Re-Circulated crankcase gases

The adaptation of emission control systems contributes to delivering to a cleaner atmosphere. The first, oldest and simplest emission control device added to an engine is the Positive Crankcase Ventilation (PCV) valve. This device introduced in the mid 1960’s was designed to capture the crankcases gases that were previously exhausted directly into the atmosphere to be re-directed into the engine via the air intake manifold. The PCV valve captures and re-directs the gases (oil, fuel, water, etc…) trapped in an engine’s crankcase back into the air intake system to be mixed with an incoming stream of air and gasoline. Once these contaminants enter the intake system, they not only contaminate the air intake system, they contribute to the build-up of carbon deposits in the combustion chamber because they do not completely burn with the fuel and due to the high heat and temperature the contaminants become carbon deposits. The reason for this occurring is that the contaminants originate from a hydrocarbon based product.

Driving conditions

A vehicle is designed to perform optimally at highway speeds (100 kph/60 mph – 120 kph/70 mph). At this speed at moderate temperature and humidity operates at a prescribed under-hood temperature delivering optimum performance from the air, fuel and (PCV) contaminants flowing into the engine while reducing any opportunity of any significant carbon build-up in the combustion chamber. However, operate the same vehicle in a traffic congested environment and all changes. The under-hood temperature and vehicle load increase affecting the normal operating settings of an engine. Optimum performance can no longer be achieved causing the air-fuel management system to make alterations that maintain a satisfactory operating condition in performance for the driver but delivers a sub-optimal power and burning process. The result is a build-up of carbon deposits – a power robbing condition.

Optimized fuel and ignition efficiency

Modern vehicles are equipped with highly sophisticated computer managed air-fuel managed systems. Many sensors measuring conditions like ambient temperature, under-hood temperature, barometric pressure, etc… contribute to delivering a prescribed level of performance and satisfaction. However the build-up of carbon deposits can lead to an increase in pressure in the combustion chamber causing the computer program to make adjustments that affect the performance negatively to ensure that the vehicle runs satisfactorily. These changes usually deliver a reduction in power delivery, fuel economy and increased emission output. This condition is usually further exacerbated by the driver as he senses the reduction in performance and usually offsets it by depressing harder on the gas pedal to get the performance expected from the vehicle. This is the beginning of an never ending downward spiral in decreased performance, poor fuel economy and carbon build-up, all of which are undesirable expectations.


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