HARNESS AS-CONTROL 3859804 - Caterpillar

Generator SetsA generator set's block load response (the percentage of rated kW that can be picked up at one time) is determined by the engine's rating and displacement. The ISO (International Standards Organization) publishes a generator set block load response curve. This curve shows that block load capability is a function of the Brake Mean Effective Pressure (BMEP) at the rating and the displacement of the engine. As rated BMEP goes up on an engine of constant displacement, the percent of rated kW block load response goes down. This is because block load response is primarily a function of displacement whereas, rated kW output is a function of displacement, fuel setting and available air. A naturally aspirated engine responds instantaneously to a block load up to its rated power. A turbocharged engine takes time to respond because of turbo inertia, before allowing the engine to develop power up to the rated point.
In certain applications, for example at altitude, the governor may add fuel faster than the turbocharger can increase air delivery. This can actually result in a situation where the increased fuel does not have sufficient air to burn and effectively "puts out the fire" in the combustion chamber. In this case, the generator set may never develop rated RPM after too large a block load is applied.
All Caterpillar engines will provide block load response in accordance with ISO guidelines. In certain applications, block load performance above the ISO guidelines may be observed, but an engine which does not perform this way should not be repaired for poor response performance.
Recently, there have been several high altitude applications which required block load response above ISO guidelines. Response improvement was gained by doing the following: ... On 60 Hertz generator sets - A 4W6117 Fuel Ratio Control Group was added. The fuel ratio control was set at + 25.4 mm (+ 1.00"). This change effectively slowed the rack while the turbocharger developed more boost pressure. Response time improved.... On 50 Hertz generator sets - A 1W1052 Turbocharger Group was installed and the static timing dimension was retarded to a setting of 24° before top dead center. These changes gave improved block load response above the ISO guidelines.
In an application which requires improved block load response, these modifications can be made by the Caterpillar dealer. Otherwise, generator set engines should be set to original Caterpillar specifications which are in accordance with ISO guidelines.