The four-cycle, six-cylinder diesel engine has about 30 degrees of crankshaft rotation during which the fuel is placed in the cylinder and begins to burn. Combustion begins on an engine operation at rated speed, this amounts to 0.002 to 0.006 of a second! Ten percent of this time is used for injection and evaporation. During the remaining ninety percent of this time, various chemical processes take place and the fuel begins to ignite as the injectors continue to feed in a specific amount of fuel.

The farther the fuel gets from the injector before ignition begins, the greater the possibility exists that not enough air will mix with the fuel for complete combustion.

Additionally, if too long an ignition delay occurs, the fuel will hit the top of the piston and condense. This will cause even further delay in fuel combustion since the diesel fuel will have to evaporate again in order to ignite. If prolonged ignition delay occurs, unburned fuel will begin to accumulate as the injectors keep spraying a regulated amount of fuel into the combustion chamber. All of the fuel will then ignite almost all at once resulting in a high rate of pressure rise and shock effect which can cause a diesel engine to "knock."

Too long an ignition delay means that the fuel is being used less efficiently because the piston is no longer in an optimum position to fully benefit from this energy release. Under such conditions it is likely that there will be some fuel that will not completely burn. This incompletely burned fuel is wasted and turns into harmful carbon and soot.

The four-cycle, six-cylinder diesel engine has about 0.002 to 0.006 of a second during which the fuel is placed in the cylinder and begins to combust. With such little room for error, combustion efficiency can easily be reduced by internal carbon and soot buildup.

Combined Factors Compound Problems

Carbon And Sludge Deposits Increase Blow-by

Gummy deposits left behind from oil getting past the piston rings bond particulate matter to the side of the piston. Deposits in this area will polish the cylinder making it difficult for the piston ring to seat properly. This allows even more blow-by to escape past the piston wall into the crankcase. Furthermore, with the keystone design of piston rings, carbon deposits will obstruct air from properly flowing down through the crevice where it is needed to force the top ring out to improve its sealing capabilities.

Unintentional Cooling Of Fuel Increases Soot Formation

The combustion chamber temperature before the fuel ignites averages 1100ºF to 1500ºF. After the fuel begins burning, a temperature of 3500ºF is possible. The temperature of the piston rarely exceeds 1000ºF. Should the fuel actually come in contact with this much cooler mass of metal, unintentional cooling of the air/fuel mixture will reduce fuel efficiency and add further to the amount of particulates building up on the piston and settling into the piston crevice. This deposit buildup also acts as an insulator and absorbs some of the energy released by the combustion process thus lowering the overall efficiency of the engine.

The Formation Of Soot And Nitrous Oxides

Fuel rich sides of the turbulent air flow are responsible for the formation of soot while the lean sides are accountable for the production of nitrous oxide.

Reducing the occurrence of lean or rich pockets inside the turbulent air flow will result in;

• Increased power output
• Reduction in the formation of soot and nitrous oxides

Problems Associated With Open Crankcase Ventilation

Water In The Crankcase

Most heavy-duty diesels have an open crankcase ventilation system with a road draft tube which relieves crankcase pressures and vents crankcase waste fumes directly into the atmosphere. One of the major problems of this system is that when the engine is shut down, the air inside the engine cools and condenses, consequently drawing in moisture-laden air. The presence of sulfur and nitrogen oxides within the crankcase has long been a point of major concern to engine and lubricant manufacturers. These contaminants, which are byproducts of combustion, combine with water inside the crankcase to create some very corrosive acids. Sulfuric and nitric acids accelerate the level of metal wear in the engine.

Acid Contamination

Lubricant manufacturers have developed additive packages that help combat the adverse effect of these acids. Among the more commonly accepted measurements of the oil's "acid resistance" is TBN (Total Base Number). Generally, the higher the TBN, the more acid neutralizing capabilities the oil has. In recent years, the makers of these lubricants have come under pressure to lower the TBN in order to comply with current emissions standards. This has created a difficult situation for the oil manufacturers. They must provide adequate protection from acid contaminants while, at the same time, lower their TBN component's contribution to harmful emissions. Another challenge facing the manufacturers of lubricating oils is to lessen the adverse impacts of soot contamination in crankcase oil.