A novel approach to extending the operating range of a low temperature combustion engine using variable lug offset with hypocycloid gear mechanism

Abstract

This study proposes a novel approach to extend the operable speed range of low-temperature combustion (LTC) engines by utilizing a variable lug offset strategy implemented through a Hypocycloidal Gear Mechanism (HGM). In this work, it is hypothesized that varying the lug offset in an HGM configuration increases the piston residence time near top dead center (TDC), thereby enhancing combustion stability under high-speed conditions. A detailed three-dimensional computational fluid dynamics (CFD) study was conducted using CONVERGE software for five different lug offset values across a speed range of 800–4200 rpm under lean mixture conditions (Lambda (λ) = 2.0). A comprehensive analysis was carried out on key parameters including in-cylinder pressure, heat release rate (HRR), indicated mean effective pressure (IMEP), indicated thermal efficiency (ITE), maximum pressure rise rate (MPRR), gas temperature, combustion phasing, heat transfer, emission characteristics such as nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2), and in-cylinder thermal uniformity. Results demonstrated that increasing the lug offset significantly extends the engine’s operational range, with stable Homogeneous Charge Compression Ignition (HCCI) combustion achieved up to 3000 rpm within the mechanically safe zone, and up to 4000 rpm under optimized phasing. The use of variable lug offset improved IMEP and ITE, with maximum thermal efficiency exceeding 45 %. Emission analysis confirmed ultra-low NOx levels and manageable HC and CO emissions within the optimal lug offset region.