Posted by Steve Dashew (April 15, 2011)
The fuel injection pumps used on diesel engines delivery precisely timed shots of fuel to the fuel injectors. The timing and volume of the fuel controls the torque and horsepower characteristics of the engine. Most engines also come with different ratings, which are typically related to the injection pump characteristics. Our Deere 4045s on Wind Horse were rated M4, 150HP@2600RPM. M4 means Deere doesn’t want the engine to run wide open more than three hours out of 24. SInce we normally operate between 1750 and 1900 RPM the engines were lightly loaded. At the other end of the rating scale is M-1 which allow full throttle 24 hours a day, and delivers 105 HP at 2300 RPM. As the max fuel we ever burn is under eight US gallons per hour, and this fighting headseas, we know that less than 80HP per engine is delivered (one gallon roughly equals 19HP). In effect, we could easily derate the engines, the benefit of which is a slightly leaner fuel burn at lower RPM. When we changed props last year in the UK we reduced our operating RPM from a max of 2600 down to 2400. Aside from being quieter, we should have gained a touch of efficiency, which was not the case. Which brings us to Everglades Diesel and the tech above. With 5200 hours on the engines we could have another 2000 to 5000 hours left to go before the pumps needed an overhaul. Or, we could have a seal problem tomorrow. SInce the R and R of the pumps is somewhat costly, we decided to rebuild at the same time we derated. The machine above turns the injection pump, and the tech measures the fuel delivered into the glass tubes as he adjusts timing and flow. The photo above is of a slightly bigger pump, ours having been completed by the time we arrived. And a close up of the fuel measuring containers to which the pump is connected. Our pumps were both about three percent high of spec, which would increase slow and intermediate speed fuel consumption. The new delivery is about six percent leaner than before. The Deere settings are the same for M1 through M3 ratings, just the max RPM changes. Theoretically, we should now be five to seven percent more efficient. Aside from verifying our drag and propulsion calculations, we also want to know how long it will take to recapture this expense. If we assume US $4.00/gallon for fuel, and we burn an average of seven gallons an hour, at six percent savings that adds up to US $1.70 per hour. The cost of derating the pumps, labor on the boat and the Everglades charge, was about US $1100 (actual costs with pump rebuilds and new injectors was more like $3000). This pencils out to less than 650 hours for payback and we have been averaging around 1000 hours a year. The data above is for the engines as they were originally set up, and that below for the new ratings. The question now, how theory works on the water, will be answered shortly.