This paper presents an investigation into the NOX reduction role played by the exhaust manifold of large-bore two stroke cycle engines by exploring the impact of the exhaust manifold design on turbocharger and engine operation. Exhaust manifold performance is defined as the ability of the exhaust manifold to: 1) optimize cylinder scavenging efficiency; and 2) minimize the pressure differential between the compressor discharge and the turbine inlet by exploiting the blow-down pressure pulses and minimizing the static pressure gradient along the exhaust manifold. Pressure pulses in the exhaust manifold have been identified as a plausible mechanism that hinders efficient cylinder scavenging and turbocharger operating range. While modifying the ports and manifold may not be cost effective, a complete understanding of and the ability to address the impact of these pressure waves on turbocharger performance and scavenging efficiency will lead to more reliable engine upgrade projects as the industry approaches the 0.5 g/bhp-hr engine. The research team chose “available energy,” or the amount of mechanical and thermal energy available to the turbocharger turbine for operation as the parameter for defining optimal exhaust manifold design parameters. This allowed the research team to: 1) investigate energy losses in the candidate Clark TLA-6 exhaust removal system on a component basis, and 2) translate the mitigation of these losses into expanded turbocharger operating range. The end point of the project was a set of exhaust manifold design guidelines aimed at maximizing turbocharger performance by way of the defined metrics, scavenging efficiency and waste-gate margin.

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