[M.D. Holloway]

Another reaction of the engine manufacturers was to create a new oil specification for EGR engines. This new specification, CI-4/SL, is designed to have a greater amount of dispersants in the oil to have the added soot remain floating about in the oil and not become attached to the metal parts on the hope that the soot will be trapped in the filters. It is safe to assume that the CI-4/SL oil has a higher cost than the previous oils. One thing to notice about this new specification is the reduction of the Total Base Number (TBN). With the reduction in the amount of sulfur in the fuel, the amount of sulfuric acid was reduced in the engine oil. This translated into a lower need for acid neutralization in the engine oil.

Caterpillar has taken a fairly unique approach to the NOx resolution problem. Caterpillar reasoned that if the combustion chamber temperature could be controlled, then the NOx issue might be cured. Cat also reasoned that if the combustion cycle could be controlled to provide a smoother burn rate, a quieter engine would be created. Caterpillar already had information on the rate of speed that the complete cycle needed to achieve a “good” burn. As a result, Caterpillar went in the direction of injecting fuel in 3 stages along with having 2 turbochargers per engine. Timing of these injections was determined by computer with engine load, engine demand, crankshaft position, throttle position and air temperature being the variables computed to determine the injection intervals. These variables also influence the choice of which turbocharger to use. The Caterpillar method goes like this:
• Before the piston achieves the position called Top Dead Center, a small amount of fuel is squirted into the combustion chamber. This will have the effect of reducing the temperature in the cylinder but will also start the combustion process at the same time.
• When the piston achieves Top Dead Center, the main fuel charge is injected into the combustion chamber. At this time, the fuel fully ignites and the power if the fuel is released. With the pilot charge already burning the pilot fuel amount, the actual rate of combustion is somewhat slower that what has been experienced in the past. This actually leads to less “clatter” associated with diesel engines. It should be noted that the temperatures in the chamber are rising at this point into the temperature range of NOx creation.
• Past Top Dead Center, a third charge of fuel is added to the combustion chamber. Again, the temperature is lowered below the critical NOx creation temperature and a slightly longer combustion time is created.

The disadvantages to this system are cost, weight, and PM. The PM is handled by the installation of a catalytic converter that Cat believes will last the life of the engine. Cat also installed a second turbocharger on their engines to enhance performance and decrease NOx. Caterpillar is the only company that has used the idea of a 3 charge fuel system. Cummins and Isuzu normally use EGR on their engines but are supplying Dodge and Chevrolet with diesel engines that use a 2 charge system. There is a pilot charge and a main charge as part of the fuel injection cycle. As a result, quieter engines have been achieved with lower NOx.

In the last few years, one method for the raising of the fuel mileage has been to use injectors that create smaller droplets of fuel in the combustion chamber. The reason for this is very simple, the smaller the droplets the more they burn in the short amount of time that they have available. Think of it this way, if you want water to evaporate in a hot room, do you throw in a bucket full as one mass or do you send in the same amount in the same time as a spray? To get the best use, you use a spray. What is the biggest problem in making the spray? Making a nozzle with the smallest holes to make the smallest drops and having a pump with sufficient pressure to get the same amount of water into the room in the same amount of time.

Let us take that idea and apply it to diesel engines. We want smaller drops, make the holes smaller. We want the same amount of fuel to go in because fuel means power. Make more holes. But more holes did not solve the whole problem nor create the necessary “fog” for the best combustion. Increase the pressure. This “increase the pressure” idea has lead to the creation of injectors that are pumping fuel into the engines in the area of 30,000 psi. While the idea of increased pressure has brought about better combustion, replacement costs of the injectors must be considered as part of the life-cycle cost of the engine. Another thing to consider is the need to keep these injectors clean. Because these holes are so small, it does not take much to plug them resulting in loss of power, increased fuel consumption, and all the rest. This has created some interesting problems for the engine manufacturers and the types of metals being used in the fuel pumps, injectors, cam shafts, cam rocker arms, and rollers. Premature and catastrophic failure of parts is on the rise and while some of it can be attributed to inadequate lubrication another proportion must be blamed on materials.