3516C Generator Sets Caterpillar

Selective Catalytic Reduction (SCR) Thermal Management

In order to maintain optimal performance of the SCR aftertreatment, load the generator set periodically to elevate the SCR inlet temperatures. For most applications, the necessary temperatures will occur naturally during the normal operation of the generator set. If normal operation of the generator set does not elevate the SCR inlet temperature sufficiently, a service procedure may be required to increase the CEM inlet temperature. The inlet temperature requirement is above 450° C (842° F) for 30 minutes or above 425° C (797° F) for 90 minutes.

The engine control system will continuously monitor the SCR inlet temperature and alert the operator when service is required. The monitor will reset if the generator set is operated to achieve the SCR inlet temperatures listed above. The SCR inlet temperature sensor can be monitored on the EMCP.

In most applications that meet the definition of standby power, service will not be required often. Possibly once every 4 or more years. In applications operating within the prime power definition, an annual service is recommended. The required temperatures will be easiest to achieve during periods of warmest ambient temperature and highest load. Ideally the temperatures will occur during normal operation, eliminating the need for a service procedure. As an example, applying 75 percent load at 25° C (77° F) ambient conditions for 90 minutes is sufficient to achieve the SCR inlet temperature and time requirements.

If the installation operates more than 2000 hours per year below 0° C (32° F) ambient temperature or 750 hours below −15° C (5° F) ambient temperature, service may be needed more than once per year. For those applications, an air inlet heater is recommended from the OEM to extend the time between servicing. Extending the time between service intervals allows for more flexible planning of service events. For example, the need for service could be delayed from winter to summer months when warmer ambient temperatures are prevalent.

Refer to table 1 to calculate the exhaust temperature at the SCR inlet. This calculation will allow the operator or dealer to predict the ability to reach the required temperatures. Complete the calculation using the site altitude, ambient temperatures, exhaust restriction, and inlet manifold temperature for the engine. The result will be an expected SCR inlet temperature. If the SCR inlet temperature cannot be achieved, consult the OEM for assistance and have the site parameters available.

Air Filter Inlet Temperature

1. Record in column B the temperature at the engine air cleaner inlet when operating at rated speed.

2. Subtract column C from column B and record the answer in column D.

3. Multiply 1.8 times column D and record the answer in column F.

Inlet Manifold Temperature

1. Record in column B the engine inlet manifold temperature when operating at rated speed.

2. Record in column C the engine TMI inlet manifold temperature.

3. Subtract column C from column B and record the answer in column D

4. Multiply 1.0 times column D and record the answer in column F.

Exhaust Restriction

1. Record in column B the engine exhaust restriction when operating at rated speed.

2. Multiply 4.0 times column D and record the answer in column F.

Altitude

1. Record in column B the altitude of installation.

2. Subtract column C from column B and divide by 100. Record the answer in column D.

3. Multiply 3.6 times column D and record the answer in column F.

Temperature Drop From Engine to CEM Inlet

1. Record in column D the temperature drop (as a positive number) from engine to CEM inlet as measured during commissioning.

2. Multiply -1.0 times column D and record the answer in column F.

Total Column F

1. Degrees Celsius that ambient site operating conditions affect the SCR inlet temperature.

2. Add Total Column F to the engine TMI Engine Outlet Temperature. The answer is the expected SCR inlet temperature of the engine at rated speed when operating at the ambient site conditions.