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Advanced Heavy-Duty Diesel Engine Piston

Description:

TECHNOLOGY AREA(S): Ground Sea

OBJECTIVE: Design, develop, and manufacture a heavy-duty diesel engine piston capable of withstanding the severe thermal stresses from a localized, periodic surface heat flux exceeding 20 MW/m2 at frequencies up to 40 Hz, with limited back-side cooling.

DESCRIPTION: Recent commercial industry trends in internal combustion (IC) engine development have focused on reducing air pollutants and fuel consumption in order to comply with environmental regulatory requirements concerning greenhouse gas emissions. Accordingly, diesel engine manufacturers have renewed their efforts to increase engine efficiency from the current status of 45% brake thermal efficiency (BTE) towards the theoretical limit of approximately 65% BTE. A pair of recent technical papers by Cummins, Inc. outlines the potential efficiency gains achieved through improvements in heat transfer reduction, friction reduction, lubricant viscosity, parasitic losses (e.g. oil and water pumps), turbomachinery efficiency, engine downspeeding, exhaust aftertreatment optimization, and last but not least, engine combustion system optimization (SAE 2013-01-2421 and SAE 2019-01-0247). This topic focuses on increasing the thermal efficiency of a 120mm-140mm bore size diesel engine through optimization of the combustion system and the resultant piston heat transfer.Engine combustion system developments include trends towards higher compression ratios, higher in-cylinder pressures (greater than 300 bar), piston bowl geometry optimization, and increased fuel injector flow rates to enable shorter combustion durations. As the combustion duration shortens and compression ratio increases, the cylinder pressure and temperature will necessarily increase, resulting in gas-side piston surface temperatures that exceed the material temperature limit (~500°C) of traditional steel piston alloys, such as 4140 steel. Another consideration when pursuing these technology developments is increased piston heat transfer. Shorter combustion durations necessitate higher localized heat fluxes (greater than 20 MW/m2) on the piston as the hot flame impinges on the piston bowl surfaces.Whereas the engine designs of commercial vehicles are heavily weighted towards achieving low emissions and good fuel economy, these attributes are less important in the design of military vehicles. Combat vehicle engines in particular should have high power density and low heat rejection, because the propulsion system competes with the vehicle’s functional systems for the total volume under armor.Thus, future combat engines designed for low heat rejection (< 0.5 kW/kW) and high output (90 bhp/L) share some of the design limits of a commercial engine, one of which is piston surface temperature. Temperatures above critical material property limits can result in reduced engine life and piston failure. Optimization of piston design for such low rejection, high power density engines while maintaining acceptable piston surface temperature is a critical step in the engine development process.The purpose of this topic is develop an advanced, heavy-duty diesel engine piston optimized for continuous, high-load operation at desert-ambient operating conditions for military ground combat vehicles. Proposals should aim to increase the peak cylinder pressure limit to 275 bar and the surface temperature limit to 600 °C, or propose technologies to reduce surface temperatures at equivalent thermal loading. The application of thermal barrier coatings to the piston crown will not be considered for this topic.

PHASE I: Conduct the engineering analysis to support the design and development of a prototype 120mm-140mm bore size piston capable of sustained operation at high-load conditions in a direct-injection, heavy-duty diesel engine. Determine the required thermal and mechanical properties and perform laboratory testing to support the selection of an appropriate material for the piston. Identify unique manufacturing requirements and conduct prototyping of a conceptual piston to demonstrate feasibility of the proposed piston technology.

PHASE II: Manufacture and test an advanced heavy-duty diesel piston prototype enabling higher combustion temperatures and pressures without compromising piston strength or durability. Develop a CAD model and engineering drawings with tolerances, surface finishes, anti-corrosion and skirt (friction) coatings, and manufacturing instructions. Develop quality inspection and approval process requirements for the prototype piston. Required deliverables include an engine test report, piston temperature analysis, CAD model, drawings, and delivery of a prototype piston to the Government’s specification.

PHASE III: Further develop an advanced diesel engine piston for use in a commercial engine, and demonstrate the piston development in a multi-cylinder engine. It is envisioned that this technology would benefit high-efficiency, future commercial diesel engines as well, especially in vehicles demonstrating engine brake thermal efficiency of 50%.

KEYWORDS: Internal combustion engine, Piston, Heavy-duty diesel, High-temperature alloy

References:

Stanton, D., "Systematic Development of Highly Efficient and Clean Engines to Meet Future Commercial Vehicle Greenhouse Gas Regulations," SAE Int. J. Engines 6(3):1395-1480, 2013, doi:10.4271/2013-01-2421.; Mohr, D., Shipp, T., and Lu, X., "The Thermodynamic Design, Analysis and Test of Cummins’ Supertruck 2 50% Brake Thermal Efficiency Engine System," SAE Technical Paper 2019-01-0247, 2019, doi:10.4271/2019-01-0247.; Pierce, D., Haynes, A., Hughes, J., Graves, R., et al., “High temperature materials for heavy duty diesel engines: Historical and future trends,” Prog. Mater. Sci. 103, 109-179, 2019, doi:10.1016/j.pmatsci.2018.10.004.; Dolan, R., Budde, R., Schramm, C., and Rezaei, R., “3D Printed Piston for Heavy-Duty Diesel Engines,” 10th NDIA Ground Vehicle Systems Engineering and Technology Symposium, Novi, MI, August 2018.; “Integral gallery containing coolant reduces piston temperature,” Sealing Technology 2016(12): 3-4, 2016, doi:10.1016/S1350-4789(16)30388-9.; Mahle GmbH (Ed.), Pistons and Engine Testing, Springer, 2016, doi:10.1007/978-3-658-09941-1.

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