Influence of hydrogen as a fuel additive on combustion and emissions characteristics of a free piston engine

Abstract

It has been shown that using fuel additives play an important role in enhancing the combustion characteristics in terms of efficiency and emissions. In addition, free piston engines have shown capable in reducing energy losses and presenting more efficient and reliable engines. In this context, the objective of the present work is to investigate the effect of using hydrogen as a fuel additive in natural gas homogeneous charge compression ignition free piston engine. To this aim, two models have been iteratively coupled: the combustion model that is used to calculate the heat release of the combustion and the scavenging model that is employed to determine the in-cylinder mixture state after scavenging in terms of its homogeneity and species mass fractions and to obtain the finial pressure and temperature of the in-cylinder mixture. In the former model, the 0-D approach through Cantera toolkit has been considered due to the fact that homogeneous charge compression ignition combustion is very rapid and the fuel-air mixture is well-homogenous, whereas in the latter model, 3-D-CFD approach through AN-SYS FLUENT software is considered to ensure precise calculations of the species exchange at the end of each engine cycle. The effect of hydrogen as a fuel additive has been quantified in terms of the combustion characteristics (e. g., ignition delay, heat release rate, engine overall efficiency and emissions, etc.). It has been shown that hydrogen addition reduces ignition delay time, decreases the incylinder peak pressure, while allowing the engine to operate with higher mechanical efficiency as it has high heat release rate, increases the NOx emission levels of the engine, but decreases the CO levels

Numerical study of the injection conditions effect on the behavior of hydrogen-air diffusion flame

“…This, offers some advantages over the EDS or EDS-finite-rate models. In addition, it allows intermediate species prediction, more thorough turbulence-chemistry coupling [6,16,31].…”

“…In addition to availability and cost issues, products derived from petroleum and natural gas provide great energy, but release large amounts of pollutants [1,2]. As a result, the international community is turning to alternative fuels, offering good ecological performance at attractive production costs [3][4][5][6].…”

Operation Range of Intermittent Velocity Control for Improving Top-Dead-Center Accuracy in Dual-Sided Free-Piston Engine Linear Generator

“…), homogeneous-charge compression ignition, and exhaust gas recirculation in free-piston engines is expected to reduce emissions and improve efficiency. [7,8,9,10,11]. Especially, the free-piston type, which is directly connected to the mover of the linear generator without using the rotary-linear motion conversion mechanism, can reduce mechanical loss by more than 40% compared to the conventional crank type [12].…”