Maintaining FORAGE HARVESTER FOR FUEL EFFICIENCY

Ronald T. Schuler

Extension Agricultural Engineer, Biological Systems Engineering Department, University of Wisconsin-Madison

Thursday, May 18, 2006

With higher fuel prices, the proper operation and maintenance of forage harvesters (choppers) becomes more important to ensure maximum forage production profitability. Some simple maintenance steps can have a significant impact on the fuel usage in harvesting alfalfa or grass silage and the machine’s capacity. A well adjusted forage harvester will require an estimated 1.5 gallons of fuel per acre. Using a fuel price of $3.00 per gallon, the fuel cost is $4.50 per acre. 

Three adjustment/maintenance steps that will have a significant impact on fuel consumption are theoretical length of cut, knife sharpness and knife/shearbar clearance. For the forage harvester, the energy/fuel consumption can be divided among 1.) pickup and feed rolls (20%), 2.) cutterhead (40%) and 3.)blowing (40%) for a properly adjusted machine. The three adjustment/maintenance steps influence the portion of the energy required by the cutterhead.

As the cutterhead knives wear, the power requirement increases. In one report, worn knives doubled the fuel requirements of the cutterhead. Therefore the estimated cutterhead fuel requirement goes from 0.6 gallons (1.5 times 0.4) per acre to 1.2 gallons per acre. For $3.00 fuel, the added fuel cost is $1.80 per acre. The added fuel requirement will be greatly affected by the degree of wear.

The power requirement increases as the knife/shearbar clearance increases. When considering a clearance of 0.01 inches versus 0.02 inches, the power requirement of the cutterhead is doubled when increasing the clearance. This result is similar to the worn knives, an increased fuel cost of $1.80 per acre. If the clearance is 0.03 inches, the fuel cost increase over 0.01 inches of clearance is $3.60 per acre. If the machine has worn knives and a knife/shearbar clearance of 0.03 inches, the added fuel cost will be estimated at $5.40 per acre.

Increasing the theoretical length of cut will reduce the fuel consumption. Carefully select the theoretical length of cut to meet the requirements of the animals and storage system. If there is a choice go with longer length of cut.

Another hidden cost with higher fuel consumption is the machine driveline wear due to the higher loads on the gears, shafts, and chains. A higher fuel usage leads to a shorter machine life.  Also the increased fuel consumption will reduce the machine capacity with respect to acres per hour and tons per hour.

Again these are estimates of the increase in fuel consumption. Nonetheless properly adjusting the forage harvester cutterhead will lead to lower fuel consumption, higher field capacity and a more profitable forage production system. The machine’s operator’s manual provides the details on adjustment procedures for the most productive operation of the forage harvester.