2002/03/01 Caterpillar

Engines:

G3606 (S/N: 3XF)

G3608 (S/N: 4WF)

G3612 (S/N: 1YG)

G3616 (S/N: 4CG)

The Engine Supervisory System (ESS) integrates several control systems and sensors that are installed in the following areas:

• Panel for the ESS

• Engine mounted junction box

• Engine

The ESS uses the Cat Data Link in order to communicate with the various control systems. This communication optimizes all of the controlled parameters in order to ensure optimal engine performance. The main components of this system are contained within the panel of the ESS. The entire system works together in order to accomplish the following items:

• The system governs the engine speed.

• The system controls the air/fuel ratio.

• The system can modify the engine timing.

• The system protects against detonation.

• The system limits the power output of the engine.

The Computerized Monitoring System (CMS) is a part of the ESS. The CMS displays important engine operating parameters. One of those important engine operating parameters is the "Engine Load". When the "GAGE GROUP SELECT" switch is in the "Gage Set 1" position, "Gage 6" displays "Engine Load". The "Engine Load" is displayed as a percentage of the available engine torque. In order to display the "Engine Load" as a digital readout, toggle the "GAGE DATA SELECT" switch until the upper readout indicates 6. The "Engine Load" parameter can also be viewed on "Screen 23" of the Digital Diagnostic Tool (DDT).

Displayed "Engine Load"

The "Engine Load" parameter that is displayed on "Gauge 6" of the CMS panel and on "Screen 23" of the DDT is an indication of engine load for the actual operating speed of the engine. After correcting for any difference in engine speed between the full rated speed and the actual speed, the actual engine load will be within ± 5 percent of the "Percent of Approximate Engine Load" value. See Table 1. This tolerance range takes into account many factors which affect engine performance. Some of these factors cannot be accounted for during the dynamometer testing at the factory. The "Engine Load" that is displayed on the CMS panel is intended to give the customer an idea of the engine's performance that is relative to the specific rating that is programmed into the personality module of the engine at the factory. The "Engine Load" parameter is displayed on "Gauge 6" of the CMS panel as a percent of the engine's full speed and load rating. The following formula can be used to determine the approximate engine load as a percentage of full speed and load rating that is programmed at the factory.

Use the formulas that follow in order to determine the "Approximate Engine Load" by using the "Full Engine Rating" and the "Percent of Approximate Engine Load".

Factors That Can Affect The Accuracy Of The Displayed "Engine Load" Parameter

The displayed "Engine Load" parameter is a calculated value that is based on following parameters:

• Engine Speed

• Fuel Flow

• Fuel Energy Content

The accuracy of the displayed "Engine Load" value will be dependent on the following parameters:

• Emissions Setting

• Misfire

• Fuel Quality

• Valve Lash Adjustments

• Fuel Correction Factor

• Prechamber Tuning

Note: In order for the displayed "Engine Load" parameter to be as accurate as possible, the engine must be properly tuned. All of the engine components must be in good working order: sensors, controls and mechanical hardware. Improper tuning and/or engine adjustments can adversely affect engine performance and the accuracy of all displayed parameters.

Engine Speed

Unstable engine operation will create inaccuracies in the displayed "Engine Load" parameter. Most industrial applications can usually maintain engine speed fluctuations to less than ± 5 rpm when the engine is in good operating condition. Generator set applications will have even better speed stability. An unstable engine is an indication of improper engine operation that is due to the conditions that follow: poor combustion, existing mechanical problems and misadjustments

Fuel Flow

Fuel flow is calculated from the inputs that follow:

• Measured Air Pressure

• Measured Air Temperature

• Measured Fuel Pressure

• Measured Fuel Temperature

• Engine Speed

• The Adjustment Of The "Fuel Energy Content" Potentiometer For The BTU Content Of The Fuel

Air pressure and fuel pressure are measured with the Air/Fuel Pressure Module. The Air/Fuel Pressure Module should be properly calibrated for the altitude of the site. Follow proper calibration procedures in the engine service manual. Air and fuel temperatures are measured by using separate sensors that are located on the engine. Ensure that the sensors are operating properly.

Fuel Energy Content

The Fuel Energy Content (BTU content) is set with the "Fuel Energy Content" potentiometer on the front of the door panel for the ESS. During the initial engine commissioning and tuning, a recent fuel analysis must be obtained in order to properly set the Fuel Energy Content (BTU content). The lower heating value (LHV) that is obtained from the fuel analysis is used to set the "Fuel Energy Content" potentiometer. The control system uses the LHV of the fuel to calculate several variables that are used to determine estimates of the fuel flow.

Emissions Level

The engine must be set for the proper emissions in order to increase the accuracy of the displayed "Engine Load". Refer to the performance specifications that are applicable for the engine in order to determine the required emissions levels. In most industrial applications, the level for NOx is 70 ± 15 PPM. For applications with leaner air/fuel ratios, the level for NOx can get as low as 50 ± 10 PPM. Refer to the information for the specific engine rating for the proper emission levels.

Misfire

Conditions that result in engine misfire will give a false indication of the displayed "Engine Load". If misfire occurs, more fuel must be supplied to the engine in order to maintain speed. The higher fuel flow directly affects the calculation for the displayed "Engine Load". Misfire can also result in the following problems: instability of the engine speed and a detonation shutdown. The engine must not be misfiring when you are determining the engine load.

Fuel Quality

Recent field experience indicates that fuel quality can possibly affect the characteristics of combustion of the air/fuel mixture. When you analyze a particular installation, the following parameters are important to know:

• Low heat value

• Methane number

• Specific gravity

• Wobbe Index

Valve Lash Adjustments

It is important for the valve lash adjustments to be correctly made for the intake valve, the exhaust valve, and the gas admission valve at the normal maintenance intervals. Incorrect valve lash adjustments can result in a combustion process that is inefficient. The valve lash adjustment for the gas admission valve has the most impact on the combustion process. Improper valve lash adjustment for the gas admission valve will affect the calculations for controlling the fuel system. This can result in the following problems: improper tuning, incorrect calculation of fuel flow, incorrect air/fuel ratio and incorrect exhaust port temperatures.

Fuel Correction Factor

The Fuel Correction Factor (FCF) is an indication of a change in the quality of the fuel. After the engine is correctly tuned, the FCF that is displayed on the CMS panel and on the DDT will be 100 percent. Any change in fuel quality will result in a change in the FCF. The FCF also affects the "Engine Load" parameter that is displayed. In order for the "Engine Load" parameter to be as accurate as possible, the FCF should be reading 100 percent. Adjust the "Fuel Energy Content" potentiometer until the FCF that is displayed is 100 percent. The engine should be in the "Combustion Feedback Mode" when the "Fuel Energy Content" potentiometer is adjusted. When no other mechanical problems and/or combustion problems exist, the displayed "Engine Load" will be as accurate as possible.

Note: The adjustment of the FCF with the "Fuel Energy Content" potentiometer is not required on a regular basis. The value of the FCF can change as much as 20 percent without any effect on the performance of the engine. In order to better understand the loading conditions of the engine, the FCF is adjusted while the engine is in the "Combustion Feedback Mode".

Prechamber Tuning

Proper prechamber tuning of the engine is critical for proper engine operation and performance. Accurate prechamber tuning requires the following items: a recent fuel analysis, a DDT for the engine and an emissions analyzer for the exhaust. The fuel analysis will determine the lower heating value (LHV) of the fuel. This LHV is used to set the "Fuel Energy Content" potentiometer that is on the front door panel of the ESS. The engine should be loaded to the expected operating condition. If the engine load is expected to fluctuate, the engine load should be set at a point that is midway between the lowest load and the highest load for the prechamber tuning. Once the loading condition is identified, the engine should be operated until normal operating temperatures are achieved. If there are no combustion problems or mechanical problems, the "prechamber tuning" can begin when normal operating temperatures are reached.

The DDT is used to place the engine in "PC CAL" mode. The desired combustion burn time and the average combustion burn time for a given cylinder are displayed on the DDT when the engine is in "PC CAL" mode.

Adjust the needle valves in order to set the combustion burn time for each cylinder to a value that is within ± 0.2 ms of the desired combustion burn time. After the combustion burn time is set for all of the engine cylinders, check the emissions levels of the exhaust. If the engine is not producing the proper exhaust emissions, adjust the "Fuel Energy Content" potentiometer. Increase the value on the "Fuel Energy Content" potentiometer in order to produce a leaner condition. Decrease the value on the "Fuel Energy Content" potentiometer in order to produce a richer condition.

The combustion burn times for the cylinders will change when the value of the BTU content of the fuel is changed. When the BTU content of the fuel is changed, the needle valves must be readjusted in order to obtain the desired combustion burn times. Check emissions levels or the exhaust again. If the engine is not producing the proper exhaust emissions, adjust the "Fuel Energy Content" potentiometer.

Continue this cycle of adjustments until the emissions levels and combustion burn times meet the performance specifications for the engine. In most cases, the final value for the BTU content that is set in the engine control system will be within ± 5 percent of the actual LHV of the fuel. This is a normal result. If your results are similar, those results should not be a cause of concern.

Tolerance Range of the Displayed "Engine Load"

The "Engine Load" parameter that is displayed on the CMS panel and on the DDT is accurate within ± 5 percent of the displayed value. If the displayed "Engine Load" does not match the calculated load or the measured load of the driven equipment, the calculated load or the measured load of the driven equipment can be adjusted in order to obtain the load that is expected. This means that the displayed "Engine Load" value could be between 95 percent and 105 percent at the rated speed.

Note: A displayed "Engine Load" value of 105 percent is not detrimental to the engine. This indicates that the conditions have changed between the settings at the factory and the settings at the site. Ensure that all of the engine performance parameters are within expected ranges. Ensure that the engine is not misfiring. Ensure that the engine does not have any mechanical problems.

If the displayed "Engine Load" value is between 105 percent and 110 percent, the following problems could exist:

• There could be existing engine problems that were not properly addressed.

• The calculation for the load for the driven equipment is not correct.

Further investigation is required. Contact your local Caterpillar Dealer for more information.

Analyzing Parameters of Engine Performance

The parameters of engine performance that follow provide important information that helps fully understand the operating conditions of the engine.

Fuel Flow

The fuel flow that is displayed on the DDT is an estimate of fuel flow through an orifice. This estimate is based on a calculation that depends on the following inputs: the fuel pressure at the engine, the fuel temperature at the engine and the factory gas constant. The fuel flow that is displayed should be accurate within ± 3 percent if the following conditions exist:

• The original orifice plates are installed.

• The settings of the gas admission valve are correct.

In cases that have engine misfire that is excessive, the displayed fuel flow that is required to maintain the engine speed will be artificially high. This will cause the displayed "Engine Load" to be excessively high. Correct the conditions that cause the engine misfire prior to further calculations for engine performance.

The actual fuel usage of the engine can be verified with an external flow meter for the fuel. The flow meter must have the properties that follow: a correct calibration, the correct size and the proper certification. Follow the guidelines in order to properly install the flow meter in the fuel supply line for the engine.

Emissions Levels of the Exhaust

The engine must be set for the proper emissions in order to achieve optimum performance. When setting the emissions levels, an engine misfire may result from an air/fuel ratio that is too lean. When setting the emissions levels, the following problems may result from an air/fuel ratio that is too rich: excessive exhaust port temperatures and a loss of detonation margin. If there is a very rich air/fuel ratio, rich misfire can occur. An emissions analyzer that has been recently calibrated is required to properly set the exhaust emissions. Do not attempt to determine the engine load without ensuring that the exhaust emissions are properly set.

Inlet Manifold Air Pressure

The Inlet Manifold Air Pressure (IMAP) of an engine is a direct indication of engine load conditions. When the engine is in good operating condition, the IMAP can be used in order to provide an accurate indication of the engine load. The following illustration provides a graph that can be used as an example. This graph illustrates relationships between IMAP and Engine Load. Use performance data that is specifically for your engine and your application in order to create a similar graph.

Illustration 1	g00872175
This illustration shows a typical graph that illustrates the relationship between Inlet Manifold Air Pressure and Load.