Effects of Amorphous Ti-Al-B Nanopowder Additives on Combustion in a Single-Cylinder Diesel Engine

Energetic nanoparticles have shown promise as additives to liquid hydrocarbon fuels due to their high specific surface area, high energy content, and catalytic capability. Novel amorphous reactive mixed-metal nanopowders (RMNPs) containing Ti, A1, and B, synthesized via a sonochemical reaction, have been developed at the Naval Research Laboratory. These materials have higher energy content than commercial nano-aluminum (nano-A1), making them potentially useful as energy-boosting fuel components rather than simply catalytic additives. This work examines the combustion behavior of these RMNPs in a small, single-cylinder, 4-stroke diesel engine (Yanmar L48V). Fuel formulations included varying fractions of RMNPs, up to 4 wt. %, suspended in jet fuel JP-5. Comparative experiments also were conducted with equivalent suspensions of nano-A1 in JP-5. For each fuel formulation, with the engine operating at constant speed of 3000 RPM, load was varied across its full range. At each load, cylinder pressure data were recorded for 30 seconds (750 cycles) to enable determination of important combustion characteristics. Although differences were small, both nano-A1 and RMNPs resulted in shorter ignition delays, retarded peak pressure locations, decreased maximum rates of heat release, and increased burn durations. In addition, a similar but larger engine (Yanmar L100V) was used to examine fuel consumption and emissions for a suspension of 8 wt. % RMNPs in JP-5 (and 8 wt. % nano-A1 for comparison). The engine was connected to a genset operating at a constant speed of 3600 RPM and constant load with nominal gIMEP (gross indicated mean effective pressure) of 6.5 bar. Fuel consumption rate was determined from time required to consume 175 mL of each fuel formulation, while emissions levels were recorded once per minute during that time. Unfortunately, combustion data and visual inspection of the injector indicated that RMNPs led to significant deposits on the injector tip and in and around the orifices, which had a negative impact on both fuel consumption rate and emissions. The engine stalled after four minutes of operation with the nano-A1-laden fuel, apparently due to clogging at the bottom of the fuel reservoir. It was concluded that particle settling in the fuel reservoir and particle clogging in the fuel system and injector were significant problems for these composite liquid/powder fuels. Nevertheless, fuel consumption rate was found to be 17% lower for the nano-A1 suspension compared to baseline JP-5 for the period of time that the engine was able to operate, which is a significant achievement towards demonstrating the potential value of reactive metal powder additives in boosting the volumetric energy density of hydrocarbon fuels.