Investigation on combustion performance enhancement and hydrocarbon emission reduction of a heavy-duty natural gas engine using eccentric intake and high-tumble-ratio flow

Abstract

To balance structural reliability and combustion efficiency in a heavy-duty natural gas engine, this study numerically investigated the effects of eccentric intake (v01) and high-tumble-ratio flow (v02) designs on a 16 L engine, using the baseline model as reference. Comparative analyses were conducted at brake thermal efficiency (1100 r/min) and rated power (1700 r/min) conditions under both equal electric control and equal peak pressure constraints. The v01 configuration enhanced in-cylinder tumble and turbulence, increasing the tumble ratio X-component nearly fivefold and turbulent kinetic energy by 7.6% at 1100 r/min. This resulted in shortened ignition delay (12–15%) and combustion duration (7–9%), with more concentrated heat release. Accordingly, v01 reduced high-pressure indicated specific fuel consumption by 0.60–0.81% and lowered unburned hydrocarbon emissions by 42.7–60.0%, while NOx emissions increased by 25–28%. Although the v02 configuration exhibited superior thermal efficiency and HC reduction, its substantially higher thermal load (51.0% vs. 32.2% for v01) raised concerns about cooling system demands and long-term durability. Given the limited efficiency gain of v02 over v01, the v01 scheme achieves a more balanced trade-off among efficiency, emissions, and thermal risk in the current evaluation framework.