Experimental Analysis of Enhanced Scavenging Efficiency in Hydrogen-Powered Internal Combustion Engines for Heavy-Duty Applications

<div class="section abstract"><div class="htmlview paragraph">The purpose of this work is to highlight the benefits of improved scavenging efficiency for premixed, lean-burn, spark-ignited heavy-duty engines fueled by hydrogen. Scavenging efficiency measures the effectiveness of replacing exhaust gases with fresh air (or an air-fuel mixture) within the cylinder of an internal combustion engine. Enhanced scavenging efficiency reduces residual gas content and increases the proportion of fresh air, resulting in a cooler local mixture temperature. Additionally, it improves heat dissipation within the combustion chamber, cooling potential hotspots and allowing for earlier injections with fewer restrictions due to combustion anomalies, particularly pre-ignitions. To increase scavenging efficiency in a 4-stroke internal combustion engine, valve timing adjustments were made by introducing a valve lift profile with greater overlap of the exhaust valve closing and the inlet valve opening sequences. Additionally, a high-efficiency turbocharger was used to reduce backpressure and thereby increase the pressure gradient across the engine and promote scavenging. A test campaign was conducted on a 12.9-liter inline 6-cylinder heavy-duty engine to determine the impact of increased scavenging efficiency. The benefits were quantified using indicators such as intake and exhaust manifold pressures and maximum power output. In addition to an engine map and a full-load performance study, start-of-injection trade-offs were made at various engine speeds, loads, and different lambda targets. The test results confirmed the anticipated improvements. The increased valve overlap, and the high-efficiency turbocharger led to enhanced volumetric efficiency and a greater negative pressure differential between the intake and exhaust manifolds. These enhancements were particularly beneficial in the high-load area, where high boost pressure is essential to achieve the desired lambda value. At lower loads, where the engine typically operates in throttled conditions with a positive pressure gradient, no deterioration was observed. In summary, implementing the scavenging concept enabled the engine to operate more stable and achieve on average approximately 15 % higher performance without experiencing pre-ignition. Additionally, the lower local mixture temperature reduced thermal stress on the combustion chamber hardware, which helps mitigate wear and potential engine damage.</div></div>