Roger M. Hoy
A new statement from our director is coming soon.
Our spring testing season is now well underway. Currently we are testing 8 models of the John Deere 8000R series. When we complete these tractors in the next few weeks, we will have 7 smaller tractors from CNH and AGCO which will complete our spring season. Last fall we tested 11 tractors. It appears that next year, we will start seeing tractors equipped to meet the next emissions levels (Tier IV interim) so we will be busy for the foreseeable future. Some of these tractors will include some new technology that will require changes to our testing practices such as the measurement of urea consumption, also known as Diesel Exhaust Fluid (DEF) and regenerating particulate filters. AGCO and John Deere have both been helpful to the lab in the past year by helping us understand these new technologies and in the case of AGCO, lending us a tractor equipped with the new technology and in the case of Deere, allowing us to visit a John Deere facility and observe a test of a regenerating particulate filter equipped engine. Many thanks are due to both companies for this outstanding support.
First, the NTTL does not, and will not, endorse any tractor or tractor manufacturer. Our mission is to provide useful, unbiased data in the form of test reports on all tractors that we test. Second, we do not endorse the practice of picking out only certain data from test reports. We believe that viewing and considering the entire test report is the best way to evaluate a tractor. Third, tractors are used in a variety of different applications: considering how a tractor will be used along with the test report is important when judging a tractor's suitability and expected operating costs. Fourth, all costs should be considered when judging operating costs. As new emission regulations take effect, we will see more tractors that consume DEF. Our experience to date, which is limited, suggests that DEF will be used at rates of around 2-4% of the fuel rate so this cost should also be considered. Next year, Nebraska Tractor Test reports will include data of DEF usage during the PTO test as we do today with fuel. Regenerating Particulate Filters may occasionally ignite diesel fuel in the exhaust manifold to raise exhaust gas temperatures to convert the collected soot to ash. We plan to provide information about this use of fuel as well in our reports. Finally, NTTL reports include specific fuel consumption information (reported as Hp-Hr/Gal and as lbs/Hp-Hr) for each measured operating point.
For our cars, miles per gallon is one way of expressing efficiency, as efficiency is commonly determined as the desired output (miles traveled) divided by the input necessary to achieve that output (gallons of fuel). For tractors, the desired output is work done, typically determined as power output multiplied by the time over which that power was delivered (Hp-hr). As with cars, the input is typically represented by the amount of fuel (gal or lb) burned to accomplish that work. Specific fuel consumption (in Hp-Hr/Gal) for a specific operating point is obtained by dividing the power output (Hp) by the fuel consumption (gal/hr). Specific fuel consumption provides one method of comparing tractors with different power levels; however, it is important to choose appropriate operating points when comparing two or more tractors. Comparisons of specific fuel consumption at maximum power are often not a good choice as it is rare for tractors used in agriculture to deliver maximum power continuously. For most PTO and drawbar applications, a tractor that delivers an average of 70-80% of available power to the implement is considered to be a well-matched application. PTO testing remains one of the best ways to compare tractors since the testing environment is well controlled and in most cases the PTO performance is directly related to engine performance and can therefore be used to estimate power, torque, and fuel consumption for various engine speeds and operating points. Drawbar testing results are also very appropriate; however, since this testing is performed outdoors, it is important to note the weather conditions. At the NTTL, drawbar testing may be conducted when the outside temperature is between 40o and 80oF. Performance results are generally better at lower temperatures. As PTO testing is typically conducted at 73oF, one can compare engine operating points between the two tests to estimate what drawbar performance results might have been achieved at other ambient temperatures. Using the drawbar and PTO test results together allows a user to estimate transmission efficiencies that cannot be seen with PTO test results alone.