Crystalline Carbon Deposition on Piston Ring Substrates and Its Effects on Tribological Characteristics, Engine Performance, and Emissions

Electron cyclotron resonance-chemical vapor carbon deposition technique was altered via incorporation of nitrogen gas in the methane (CH₄)-based plasma, thermal annealing of the substrates, and Arduino-controlled sample rotating mechanism to bombard the contact surface of the piston ring samples. By placing the substrates very close to the plasma gun, various carbon-based structures including graphene oxide, nanodiamond, and reduced graphene oxide were successfully deposited. The formed structures were characterized via scanning electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray diffraction, and energy dispersive X-ray. Related tribological analyses such as surface hardness-roughness, coefficient of friction (COF), and wear rate were also carried out on the coated surfaces. The morphology and chemical composition of the worn surfaces were observed via SEM and EDX. The coated samples were installed in a small spark-ignition engine to determine the effect of coating on brake power (P_e), specific energy consumption (β), carbon monoxide (CO), and unburned hydrocarbon (UHC) emissions. Very promising results of 14% increase in surface hardness, 11% reduction in β, 15% enhancement in P_e, 50% decrease in COF, 12.5% and 9% improvements in CO, and UHC emissions were obtained.