propane fueled tractor demonstration
TRANSCRIPT
04FFL-61
Propane Fueled Tractor Demonstration
Brian J. Birch Southwest Research Institute
Copyright © 2004 SAE International
ABSTRACT
Southwest Research Institute® (SwRI®) has developed a modern propane-fueled John Deere 5410 tractor through funding provided by the Propane Education and Research Council (PERC) and the Texas Alternative Fuels Council with support from the John Deere Product Engineering Center. The project began in June 2001 and the tractor was completed in March 2002. The results from this development were published in SAE paper Number 2003-01-1923 titled: “Development of a Clean, Efficient, Propane-fueled Tractor” and presented at the 2003 JSAE/SAE International Spring Fuels and Lubricants meeting in Yokohama, Japan. This paper presents the second phase results from the tractor demonstration in a field test environment.
The original project objective was to develop an efficient propane-fueled engine capable of achieving the EPA Tier 3 emissions standards and to incorporate this engine into an agricultural tractor as an alternative to diesel-powered equipment. Use of diesel powered equipment contributes to ozone formation and particulate matter emissions, both air quality concerns. Large numbers of tractors of this size are used in both rural and urban settings for such tasks as mowing, right of way maintenance, etc.
Following the completion of development, a follow-on project was pursued to demonstrate the tractor in realistic field conditions. The prototype tractor was operated and monitored at one of John Deere’s primary test locations in Riverdale, California. A total operating time accumulation of 650 hours was reached, operating under a variety of test cycles. Data was collected during this testing, and a complete engine teardown was performed upon test completion. The data analysis and inspection revealed no major concerns related to robust operation. This paper describes the testing procedures, analysis, results, and duty cycle evaluation following the demonstration testing. The prototype propane tractor is shown in Figure 1.
Figure 1: Prototype Propane Tractor
INTRODUCTION
This project benefits both the agricultural and propane industry. The main benefit to agriculture is the availability of a new alternative for diesel-powered equipment. The potential benefits of a clean propane-fueled tractor would be most apparent for the agricultural users situated in ozone non-attainment areas. These tractors would deliver a significant reduction in NOx and reactive hydrocarbon emissions compared to diesel use. [1] Reductions in these pollutants would lead to a large reduction in the ozone-forming potential of the exhaust emissions from agricultural equipment. Particulate emissions would also be greatly reduced compared to existing diesel engines. As air quality regulators’ awareness grows of the contribution made to air pollution by off-road equipment, use of clean engines may delay or prevent the enactment of regulations that prohibit the use of diesel-powered equipment during periods of maximum ozone formation.
Use of diesel powered equipment in an urban environment contributes to ozone formation and particulate matter emissions, which are both air quality concerns. According to the Equipment Manufacturers Institute, in 1999, 47,181 tractors in the 30 – 75 kW range were sold in the U.S. The two states with the most purchases were Texas and California, both states that have documented air quality problems. [1]
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ALTERNATIVE FUELS AS A POTENTIAL SOLUTION – A potential solution to diesel exhaust emissions concerns is to switch from diesel fuel to alternative fuels such as propane and natural gas. In particular, the diesel emissions problem has been largely solved through the development of lean-burn, spark-ignited natural gas-fueled engines. The emissions from these engines, if developed correctly, can be quite low, with NOx
emissions of less than half the current standard for diesel engines as well as negligible particulate emissions that are considered a carcinogen in California. Also, the efficiency of these engines has improved steadily, and fuel economy is nearly on par with that of diesel engines. Natural gas engines have been highly refined in the past few years, and provide substantial emissions reductions while being competitive in operating costs. The main application of these engines to date, however, has been in urban transit and school buses. In these applications, fuel is typically stored as compressed natural gas (CNG) in large cylinders at pressures up to 25 MPa. Although the storage density at these high pressures is relatively high, CNG requires roughly 4.5 times the storage volume for an equivalent amount of diesel fuel, and the tanks tend to be large cylindrical pressure vessels. Providing high pressure refueling facilities for CNG vehicles at remote locations is also a concern as a gas compressor and access to a gas pipeline are required. These factors make CNG fuel impractical for most off-road vehicles.
USE OF LPG FUEL – A more practical solution for offroad vehicles, such as agricultural tractors, is to use liquefied petroleum gas (LPG). LPG consists of hydro-carbon mixtures primarily composed of propane (>90%). LPG, as an off-road engine fuel, offers several advantages over CNG. One such advantage is that it can be stored as a liquid under relatively low pressures. This significantly increases the fuel storage density; e.g., liquid propane has a storage density that is 2.5 times that of CNG (for CNG stored at 20,680 kPa). Along with increased onboard fuel storage, a liquid fuel is more portable and is readily delivered to farms or remote work sites. Propane is commonly delivered to most farms across the Midwest today. Another advantage that propane has over natural gas is the existence of recognized specifications for engine fuel, such as HD-5 or HD-10. In particular, the HD-5 dictates a fuel composition that is primarily propane, i.e. greater than 90%. A typical HD-5 fuel would be approximately 96% propane, so its properties would be similar to that of pure propane. A high percentage propane fuel has a fuel structure with a high hydrogen/ carbon (H/C) atom ratio. This gives it several desirable qualities. First, a high H/C ratio corresponds to a relatively high motor octane number. For a typical HD-5 fuel composition, the motor octane number would be about 97. High octane numbers allow the use of high compression ratios, and also allows the engine to be operated at high power densities. A high H/C ratio yields lower greenhouse gas emissions, since for each unit of fuel burned, less CO2 is formed. Also, propane has a related advantage in terms of ozone
reactivity. The unburned hydrocarbons that are released into the environment tend to have a lower ozone-forming potential than fuels such as gasoline or diesel fuel. Further, since propane has a low lean flammability limit (similar to natural gas), it can be used as a fuel for lean-burn spark-ignition engines. Therefore, the considerable development work that has been conducted on lean-burn CNG engines can serve as a base for future propane engine work. [1]
Propane is also readily available. It is derived from nat-ural gas processing and petroleum refining, and there is a large domestic supply. Distribution is provided by a 112,654 Km interstate pipeline distribution network and about 25,000 retail outlets. In fact, propane is the leading alternative fuel for vehicles in the U.S., with currently 71% of alternative-fueled on-road vehicles operating on propane. [2]
In order to prove the feasibility of this technology, it was necessary to place the prototype tractor into a field environment for testing and evaluation. This served two purposes: to validate the performance of the tractor in true field conditions, rather than laboratory situation, and to enhance manufacturer and public awareness of new technology available for propane-fueled equipment. PROJECT OBJECTIVE AND GOALS
The objective of this project was to demonstrate, in field conditions, successful operation of a clean, modern propane-fueled tractor. The goal of the project was to effectively replace a diesel-powered tractor in terms of performance, operator acceptance, and operating cost. A direct benefit from this project to the propane industry would be a new application for propane fuel and the resulting increase in sales. Depending on the region in which it is operated, a majority of this propane likely would be consumed in the summer months when normal demand is low. This will serve to balance out the current seasonal demand for propane.
COMPARISON BETWEEN PROPANE AND DIESEL ENGINE CONFIGURATIONS
The propane tractor engine development program was completed in March of 2002, and included propane fuel system addition, development level engine control unit, engine calibration, emissions testing, performance testing, and noise evaluation. The final converted LPG engine emissions, output power, and noise emissions compare favorably to the original diesel configuration. A comparison to the baseline diesel engine is provided in Figure 2. This plot shows that the diesel engine greatly exceeds the Tier 3 limits in terms of NOx + NMHC and PM. Although the propane engine produced slightly less power (~ 8 %) than the diesel engine, the NOx + NMHC
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emissions output was substantially reduced. The propane engine NOx + NMHC was approximately 44 percent that of the diesel engine. This reduction was primarily due to a large decrease in NOx, since the NMHC emissions from the propane engine were higher. The propane engine and diesel engine have similar CO levels. The propane engine had significantly lower particulate matter (PM), with a 92 percent reduction compared to the diesel engine. [1]
Figure 2: Comparison of Diesel and Propane Engine Emissions
The torque curve measured from the propane engine using the 55 kW rated power calibration is shown plotted relative to that of the baseline diesel engine in Figure 3. As the plot shows, the propane engine’s torque curve falls between the continuous and intermittent ratings for the stock diesel engine configuration. [1]
Figure 3: Comparison of Diesel and Propane Engine Performance
A thermal efficiency comparison can also be made between the two engines. Figure 4 shows a comparison of the thermal efficiency in terms of the overall thermal efficiency measured over the 8-mode emissions test cycle. This number is more representative of the relative fuel efficiency that would be seen during typical operation, which is a mix of full and part load operation.
The efficiency numbers shown were calculated from the fuel consumption at each of the 8 modes in the ISO 8178-C1 cycle with the appropriate weighting factor applied to each mode. Note that the efficiency drop with the propane engine compared to the diesel engine is approximately 8.6 percent. This reduction is less than that which is typically seen (e.g. 25 percent) when comparing a typical propane engine and a diesel engine. Much of this improvement is due to the use of lean burn combustion and optimal calibration of the air-fuel ratio and spark timing at part loads. [1]
Figure 4: Comparison of Diesel and Propane Cycle Weighted Thermal
Efficiency
Noise emissions from the propane engine were also measured. Large reductions in noise were obtained with propane operation as compared to the baseline diesel. Figure 5 shows the reduction in noise, measured 1 meter from the top and front of the engine respectively. For reference, a 6 dB decrease is equivalent to a 50 percent reduction in noise, so the overall noise reduction was significant at all operating points. [1]
Figure 5: Comparison of noise output levels for Diesel and Propane engine configurations
DEMONSTRATION PREPARATION
Comparison of 8-Mode Emissions ResultsJohn Deere 4045 Diesel vs. Propane Engine
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Cycle Weighted Thermal Efficiency Comparison John Deere 4045DLV50 Diesel vs. 4045 Propane Engine
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This section describes the preparation process for the demonstration including test site selection, and tractor modifications.
TRACTOR TEST SITE LOCATIONS
SwRI selected the final test site in cooperation with John Deere engineering at a test vineyard in Riverdale, California. The duty cycles selected for the tractor operation are shown in Table 1.
Table 1: Estimated Tractor Duty Cycle for John Deere Test Site
Tractor Function Duty Cycle Time
Vineyard Tilling Heavy 90 Hours/Week
Vineyard Planting Medium 50 Hours/Week.
Vineyard Spraying Light 90 Hours/Week
Fertilizer Spreading Light 60 Hours/Week
PROPANE TRACTOR PRE-TEST MODIFICATIONS
The following upgrades were made to the propane tractor following the submission of the SAE paper Number 2003-01-1923 titled: “Development of a Clean, Efficient, Propane Fueled Off-Road Tractor”.
Ø Rear propane tank remounted to stock diesel tank mounts without modification to the stock Roll Over Protection System (ROPS)
Ø Governor switch added to switch between 1500 rpm and 2400 rpm Power-Take-Off (PTO) outputs
Ø Starter lockout switch added to increase user security
Ø Data acquisition system added with complete instrumentation including:
• Air/Fuel ratio with second UEGO wide band O2 sensor
• Coolant Temperature with K-type thermocouple
• Mass Air Flow with hot-wire anemometer • Pedal position • Throttle position • Fuel trim valve position • Manifold air pressure • Fuel lock-off valve status • Malfunction indicator light • Engine Speed
A PTO governor speed switch was added to the dash to control the output speed for various implements. A label was added that allows the user to select between a governor speed of 1500 rpm and 2400 rpm. The data acquisition control box was added under the driver’s seat to allow for easy access. Every two to four days, the
operator was required to open the box, and swap the memory storage card.
Figure 6 is an illustration of the various additional sensors added for this demonstration project. A second O2 sensor was added to avoid complications with the control system. A mass air flow sensor was added to aid in the calculation of fuel consumption (used in combination with air/fuel ratio data from O2 sensor). In addition, an isolation mount was added to the fuel lines, in order to protect the lines from vibration during operation.
Figure 6: Additional Instrumentation
VEHICLE COMPLIANCE TESTING
Prior to shipment of the propane tractor to John Deere for demonstration and test site verification, the tractor was analyzed by the Texas Railroad Commission (RRC) for propane vehicle compliance. The Gas Certification Division of the Texas RRC is the main governing body for propane and Compressed natural gas vehicle conversion compliance testing for the state of Texas. The propane tractor was certified with a recommendation to add guards around the propane tank valves to protect them from being hit directly. Figure 7 illustrates the rear propane tank valve guard, while Figure 8 illustrates the lower tank valve guard. Due to the location of the front tank valve, no additional protection was necessary.
Oxygen Sensor for DAQ
Oxygen Sensor for controller
Mass Air Flow Sensor for DAQ
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Figure 7: Rear Propane Tank Valve Guard
Figure 8: Lower Propane Tank Valve Guard
DEMONSTRATION
The tractor was tested at the John Deere, Riverdale, California test site for a period of approximately five months to accumulate a total of 650 hours. This period was used to both accumulate operating hours on the tractor, and to determine if there were any obvious durability or reliability problems with the prototype equipment on the tractor.
The tractor was used in a variety of applications, such as tilling, mowing, planting, and fertilizer spreading. Fuel consumption records were kept to determine the overall fuel use of the tractor. Also, feedback from the operators was solicited to determine if any problems exist with the tractor. Problems were rectified as soon as possible during the program to minimize downtime for the operators. Figure 9 shows the tractor on-site in Riverdale.
Figure 9: Tractor On-site in Riverdale with Vineyard Section in
Background
DEMONSTRATION REVIEW
This section describes the analysis and review of all data taken during the demonstration process. In addition, fuel consumption, operator review, engine teardown results, and duty cycle analysis is summarized.
TEST CYCLES
While on site at the test site in Riverdale, California, the propane tractor was required to perform several duties as part of a normal fleet for maintaining a 600-acre vineyard. Most of the tasks involved are considered medium to heavy-duty, and are standard operating conditions for this type of tractor in the standard diesel configuration. No concessions were made to accommodate a lighter load role for the propane fueled tractor. This allowed for true, real-world data accumulation, endurance evaluation, and operator review. Table 2 lists the tasks performed by the propane tractor during the demonstration process, with the corresponding timing information.
Table 2: John Deere Test Site Demonstration Task Summary
Tractor Function Duty Total Time Vineyard Disking Heavy 154.9 hours Vineyard Tilling/plowing Heavy 45.9 hours Vineyard Mowing Medium 197.1 hours Vineyard Spraying Light 181.5 hours Manure Spreading Light 26.1 hours Fertilizer Spreading Light 32.9 hours Road time Light 11.8 hours
Total hours 650.2 hours
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DATA RESULTS
Prior to the demonstration, the propane tractor was instrumented and equipped with a data acquisition system to record the following parameters during testing:
• Air/Fuel ratio • Coolant temperature • Mass air flow • Pedal position • Throttle position • Fuel trim valve position • Manifold air pressure • Fuel lock-off valve status • Malfunction indicator light
Following the test completion, all data was downloaded from the data acquisition system, and compiled using Microsoft Excel. From this data, it is possible to determine the engine loads, engine temperatures, fuel consumption, and any operating problems or issues during testing. Note that this data was intended as a sample of the overall test duration, and does not cover the entire 650 hours of operating time. Using the operator logs as a reference, it is possible to determine the tractor activity during the logged data time. Table 3 summarizes the sampled data and corresponding tractor duty. Average duty cycle information and fuel consumption is calculated from this sample.
Table 3: Data Acquisition Summary
Data Sample Date
Tractor Function
Tractor Duty
11/26/2002 Tilling/Plowing Heavy 11/27/2002 Tilling/Plowing Heavy 01/27/2003 Manure Spreader Light 01/28/2003 Manure Spreader Light 02/05/2003 Berm Spraying Light 02/06/2003 Berm Spraying Light 02/07/2003 Berm Spraying Light 02/26/2003 Berm Spraying Light 02/27/2003 Berm Spraying Light 02/28/2003 Berm Spraying Light 02/19/2003 Mower Medium 02/20/2003 Mower Medium 02/21/2003 Mower Medium
The data is separated by test date, and recorded at a 1 Hz sampling rate. The operator initiated data sampling when the tractor key was turned to the ON position. Figure 10 through Figure 13 illustrate the tractor operating cycles for the entire day of February 28, 2003. During this test day, the tractor was involved in berm spraying, and was using the 2400 rpm governor speed setting. The lean burn combustion strategy is evident in Figure 10, with an average air/fuel ratio of 21.5:1. This calibration resulted in an exceptional thermal efficiency and overall fuel consumption comparable to the diesel engine. [1]
Figure 10: Propane Tractor Operating Cycle, February 28, 2003: A/F
Ratio Measurement
The overall duty cycle for the tractor operation can is illustrated in Figure 11 and Figure 12. It can be seen that for the berm spraying operation, the tractor engine was operated between 10% and 55% throttle for approximately 90% of the day. Engine load averaged 62 kpa, only reaching peak load for short time periods. During this time, the PTO switch was activated to limit the electronic governor speed to 1500 rpm.
Figure 11: Propane Tractor Operating Cycle, February 28, 2003:
Throttle and Pedal Position Measurement
Figure 12: Propane Tractor Operating Cycle, February 28, 2003:
Manifold Air Pressure Measurement
Fuel flow was calculated using the measured mass air
John Deere Propane Tractor2/28/2003
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flow and air/fuel ratio at each operating point. Figure 13 shows maximum fuel flow values corresponding to the observed maximum engine load and throttle opening values during the operating day. The calibration at the higher load points allowed for a lower air/fuel ratio during the high load points to increase horsepower, and eliminate misfire.
Figure 13: Propane Tractor Operating Cycle, February 28, 2003: Fuel
Flow Measurement
FUEL CONSUMPTION
Fuel consumption is a major issue relative to the potential success of the propane tractor in the off-road vehicle market. In an area led primarily by diesel fueled engines, fuel efficiency will play a major role in the promotion of this new technology. For this demonstration, fuel consumption relies on the data sampled using the data acquisition system that measured the air-flow and resulting air/fuel ratio in order to calculate fuel flow. In addition to the overall average, the fuel consumption can be separated for each duty using the operator log sheets. Table 4 compares the fuel consumption during the various tasks. As a reference, Riverdale test site engineers report an average diesel fuel consumption of 1.8 gallons/hour for 5420 model tractors over all duties.
Table 4: Average Fuel Consumption
Tractor Function
Data Acquisition Average Fuel Consumption
(gal/hr)
Tractor Function
Data Acquisition Average Fuel Consumption
(gal/hr)
Vineyard Tilling/ Plowing
4.42 Vineyard Spraying 1.23
Vineyard Mowing 1.08
Fertilizer Spreading
3.23
Manure Spreading 2.18 Vineyard
Disking 1.84
Average 2.33 (gal/hr) vs. 1.80 (gal/hr) diesel reference
To compare the fuel consumption data measured during the demonstration test, the fuel consumption data during laboratory testing was compared. Table 5 and Figure 14 illustrate the fuel consumption during the propane tractor
engine development during wide-open throttle, full load. [1]
Table 5: Propane Engine Wide Open Throttle Fuel Consumption
Engine Speed (rpm)
Fuel Flow (lb/hr)
Power (Hp)
Load Factor
Fuel Flow
(gal/hr) 2399 27.14 74 1 6.52 2399 22.5 54 0.72 5.40 2399 17 36 0.48 4.08 2399 12 18 0.24 2.88 2398 10 7.2 0.09 2.40
Figure 14: Propane Tractor Load Factor vs. Fuel Consumption Rate
DUTY CYCLE ANALYSIS
In order to determine the average loads on the propane tractor engine, the manifold air pressure was measured using the data acquisition system during the sample cycles seen in Table 7. From this data, combined with engine speed and throttle position, it is possible to estimate the duty cycle for this tractor as operated in real-world conditions. To calculate the amount of time spent at various load points, the intake manifold pressure was compiled over each of the tasks sampled using the data acquisition system. Figure 15 through Figure 18 illustrate the percentage of the total operating time, and the corresponding operating time at that respective load for berm spraying, mowing, manure spreading, and tilling, respectively. Figure 19 shows average duty cycle over the entire sample. From this, it can be seen that the tractor operates primarily between 10 percent and 55 percent load. In addition, it can be seen that the average sample represents the individual tasks very well in terms of duty cycle percentage.
John Deere Propane Tractor2/28/2003
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Figure 15: Duty Cycle Using Berm Sprayer
Figure 16: Duty Cycle During Mowing
Figure 17: Duty Cycle During Manure Spreading
Figure 18: Duty Cycle During Tilling/Plowing
Figure 19: Duty Cycle Average
ENGINE TEAR DOWN RESULTS
Following the completion of 650.2 hours of real world testing, the propane tractor was returned to SwRI for final teardown and inspection.
In order to analyze the effects of the propane conversion on internal engine components, the head, valves, pistons, and rods were removed. During this inspection, no abnormal wear was found on any engine component. Valve recession was minor, the combustion chamber and piston crown were free of deposits, and the liners maintained a clear crosshatch pattern. Wear and deposit amounts were comparable to the diesel engine with similar operating time tested previously by SwRI. Figure 20 illustrates the teardown process following the tractor’s return to the SwRI facility.
Figure 20: Propane Tractor Teardown
CONCLUSION
This project was successful in proving the feasibility of propane technology for use in the off-road market by placing the propane prototype tractor into a real-world environment for field-testing and evaluation. This testing validated the performance of the SwRI developed
LPG Tractor Duty Cycle using Berm Sprayer
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propane tractor during real world conditions, rather than a laboratory situation, and enhanced manufacturer and public awareness of the new technology available for propane-fueled equipment. During a variety of required duty cycles, the propane tractor was successful in replacing a diesel-powered tractor in terms of performance, operator acceptance, and fuel consumption. Figure 21 is a photograph of the prototype tractor prior to demonstration.
Figure 21: Photograph of Prototype Tractor Prior to Demonstration
ACKNOWLEDGEMENTS
The author would like to thank the engineers and operators from the John Deere Riverdale test site for all of their support during this project. Their open minds and diligence helped insure success. REFERENCES 1 SAE Paper #2003-01-1923: “Development of a
Clean, Efficient, Propane-fueled Tractor”, Brian J. Birch, John Kubesh, Southwest Research Institute
2 Final Report: “Development if a John Deere 300 Series Natural Gas Engine” John T. Kubesh, Southwest Research Institute, 1996
CONTACT
Brian J. Birch Advanced Combustion and Emissions Section Engine, Emissions and Vehicle Research Division Southwest Research Institute 6220 Culebra Rd San Antonio, TX 78258 (210) 522-2034 [email protected]