Design and Optimization of Exhaust Manifold For Volvo Penta D6

Abstract

The Volvo Penta D6 is a high-performance diesel engine specifically designed for marine applications. Its efficiency relies heavily on the turbocharger, making it crucial to retain as much energy as possible from the exhaust gases. However, the current water-cooled exhaust manifold reduces the available thermal energy by cooling down the exhaust gases, which affects turbocharger efficiency. The water-cooling of the exhaust manifold is necessary due to regulations of 220 ◦C maximum temp for engine surfaces. The limit is important because engines often operate in tight compartments, sometimes with multiple units nearby, where there is a risk of diesel fuel leaking directly onto hot engine parts. The water-cooling of the exhaust manifold is also problematic for implementation of future after-treatment systems such as SCR, as the current exhaust gas temperatures are to low.

This thesis presents a 1-D simulation study in GT-Power to explore how reducing heat loss in the exhaust manifold could enhance engine performance. An engine model of the D6 engine was analyzed and then used to simulate different scenarios such as changes in manifold geometry, levels of heat loss and turbo chargers. A few important conclusions are listed below: • Only changing the geometry of the exhaust manifold while keeping the cooling unchanged is beneficial. • Reducing the cooling of the original exhaust will not improve the performance, but rather make the engine perform worse. However, combining reduced cooling with a more capable turbocharger is beneficial.

The simulations showed that changing from a single exhaust pipe to a two-pipe system, without making any changes to the water cooling, improved performance and fuel efficiency. It resulted in a 4.5% increase in peak power and a 2.5% reduction in Brake Specific Fuel Consumption (BSFC).

Further simulations indicated that reducing the heat lost in exhaust manifold with 78% from the original watercooled exhaust to a insulated dry exhaust system led to a worse performance, with peak power decreasing by 1.7% and a less desired torque curve with a large dip around 2400 rpm. This occurred because the increased exhaust pressure and mass flow pushed the turbocharger out of its optimal efficiency zones. Based on those discoveries, a new larger turbocharger was simulated with the same insulated system, showing increase in performance of +4.3% and BSFC reduction of 2.7%, just by supplying more air efficiently.

Further simulations explored how waste-gating could successfully increase exhaust gas temperature, and how changes to injection timing and amount of fuel complimented the benefits of increased exhaust enthalpy. A final configuration of the engine that combined a two bank system with exhaust flow from three cylinders in each bank to get a pulse divided exhaust manifold with less cooling together with a GT45 turbo, advanced timing and a increase in fuel it became possible to success fully meet Volvo Penta’s target of 550 hp without increasing the NOx emissions.

This thesis demonstrates the possibility to unlock performance potential by reducing the heat being currently lost in cooling. It mentions the technical modifications required to harness that energy while maintaining emission levels and safety requirements.