Lightweight 0.4 – 3 kW Soldier-Portable JP-8/DF-2 Generators.

Timothy LaBreche, Dave Spence, Rich Mastanduno, Subir Roychoudhury

Precision Combustion, Inc., 410 Sackett Point Rd., North Haven, CT 06473

tlabreche@precision-combustion.com

Abstract:

Precision Combustion, Inc. (PCI) has developed a line of battery-hybridized generators by utilizing reliable, lightweight and low-cost, commercial, off-the-shelf (COTS) 4-stroke engines. The fueling system is modified to operate on JP-8/DF-2 via PCI’s novel and patented octane-matching approach. 0.5 and 1 kW prototypes have been matured. Capability for tethering 3 generators and obtaining up to 3 kW has been demonstrated. Custom power electronics enable simultaneous DC and AC outputs. MIL-SPEC environmental and power quality testing has been successfully completed. 1000-hour durability testing has indicated no abnormal wear and tear or impact on normally expected life. Maintenance intervals were between 100 – 150 hours with no irregular buildup of fuel or metals in the oil. The approach also avoids wet stacking. TEC-D (Technical Demonstration) testing at Fort Devens has also been completed without any technical issues identified during testing with various appliances. The 400 W generator has a dry-weight of less than 18 pounds and is ruck-packable. It includes electric start and consumes less than 0.07 gallons of JP8 per hour. The 1 kW version weighs 30 pounds and in addition to AC, it has full range DC output as an option. Stable operation with other liquid and gaseous fuels has also been demonstrated for multi-fuel capability. Any COTS engine can be suitably adapted. The particular engines used were chosen for reliability, low noise and availability.

PCI has also developed tethering technology that leverages our power electronics to create a load-sensitive network of 1kW generators. The modular approach permits load matching so that only the generators needed are operating. This increases efficiency, reduces maintenance, and eliminates wet stacking compared to the TQG or MTG at part load. This enables multiple single soldier portable generators to be daisy-chained for producing up to 3 kW (compared to the much heavier and larger 2 kW MTG (MEP-531A; 123.5 lbs) or the 3kW TQG (MEP-831A; 304 lbs).

PCI’s proven octane-matching approach is inherently superior to other “fogging” approaches for enabling spark ignited (SI) engine operation on JP-8. SI engines require octane numbers of >80 for stable operation and avoiding knock, yet JP-8 has an octane number of only ~20. PCI uses its in-situ and on-demand JP-8 upgrading reactor (the

size of a D-cell battery) and an advanced direct fuel injection approach to upgrade the octane and thereby reliably operate SI engines on JP-8 or other liquid and gaseous fuels. No carburetor, special start fluids or starting procedures are required. This also allows attitude independence during operation. The JP-8 upgrading reactor is tolerant to 3000 ppm sulfur (JP-8 spec) and its performance has been proven over 1000’s of hours of testing. Test data will be shared during the presentation.

Keywords: Portable, Packable, PPG, Reforming, Fuel Processing, Power Generator, JP-8, Diesel, APU

Introduction Commercial off-the-shelf gasoline engines are inexpensive and meet the weight, size, and power output requirements for the deployed soldier. These engines however run on gasoline, a high octane fuel (octane number 85-100). As a result, these engines cannot operate with JP-8 heavy fuel, whose octane number is in the range of 15-25. Multiple alternative means developed to allow operation on JP-8 are inherently flawed due to their reliance upon approaches that do not actually overcome the core octane number problem.

PCI’s approach The octane number of JP-8 fed to the engine was directly increased to the 80+ range, suitable for operation of SI engines via “Octane Matching”. The JP-8 is instantaneously (order of milliseconds) converted to high octane fuel, immediately prior to injection into the combustion chamber via an extremely compact (C-cell battery size), octane-boosting reactor. PCI’s underlying CPOX reactor breakthrough has been advanced in collaboration with automotive and DoD support. 0.3 – 1 kW versions of the generator have been matured for meeting field battery charging needs with JP-8. PCI’s Fuel conditioning Module (FCM) for the Soldier Power Genset (SPG) series of generators is based on the concept of converting any spark ignited commercial off the shelf (COTS) gasoline generator to run on low octane, heavy distillate fuels such as JP8 or diesel. Over the course of the program, a kit was developed that is adaptable to run a wide range of engine makes, models and power ratings by changing a small number of components and control variables. This makes the technology relatively engine agnostic over a wide range of power levels.

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In order to operate the balance of plant components during startup of the FCM a system battery was required. The battery needed to be robust enough to handle operation of these components, while also being lightweight and power dense. Once the system was operating, the control and power electronics were capable of recharging the battery. Several potential options were studied prior to the selection of a battery capable of producing the required power while still being small enough and light enough to be integrated into the generator system.

The primary requirements with respect to control and power electronics were to provide high fidelity fuel conditioner operation and reliable integration with the engine to properly meter fuel at steady state and transient conditions. The power electronics were implemented to provide reliable AC and DC power as well as providing power management between the balance of plant components and the rechargeable onboard battery. A logical stepwise progression of both hardware and software was employed over the course of the program to allow for requirements to be identified and improvements to be made through several iterations. The hardware was matured in stages and software was continuously modified and improved for maximum benefit to the genset system.

Transient response testing consisted of multiple loading cycles performed at each power level tested during durability evaluations. The transient response testing was then repeated after the testing was complete for both AC and DC power outputs. The results of this testing can be seen in Figures 1 and 2. Engine oil temperatures are also shown. Note the stable AC and DC outputs during transition.

 

Figure 1: Max power and transient testing performed prior to the endurance test.

 

Figure 2: Transient testing performed on both AC and DC loads after the endurance testing. No change in performance was observed before and after the 100-hour test.

Engine Oil Analysis PCI measured oil compositions on several development test engines and compared results to unused engine oil. The figures below summarize oil composition analysis measurements made on 3 different engines with run times of 94 to 335 hours. No meaningful change in oil properties were observed after operation with JP-8 (i.e. no JP-8 dilution of crankcase oil) (Figure 3). Note: Manufacturer recommended oil change interval is 100 hours. Contamination of the oil by fuel leaking past the piston rings has been a concern noted with other JP-8 conversion technologies. The oil analysis from the engines fitted with PCI’s FCM showed < 1 percent fuel in the engine oil, demonstrating a key benefit to PCI fuel conditioning approach and further confirming the 100 hour oil change interval recommendation. Figure 3 shows the results of the analysis.

 

Figure 3: Results of oil analysis examining fuel percentage in engine oil over several hundred hours showed no JP-8

dilution in crankcase oil.  

 

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Conclusions

The feasibility of converting a lightweight gasoline engine without any internal engine modification, and operating on distillate fuels (i.e. diesel and JP-8), in addition to gasoline was clearly illustrated. Four units at TRL of 7 were developed. The generators were capable of starting and operating in varied weather and temperatures, maintaining speed and voltage during load transitions and operating safely for long periods. PCI’s fuel conditioner module has also shown to be applicable to a wide range of makes, models and power outputs of gasoline generators that are readily available today.

Acknowledgements 

We acknowledge the support of the DoD (CERDEC, Picatinny Arsenal, and WPAFB). Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the DoD and DOE.

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