Exploring light-duty internal combustion engine boosting and exhaust compounding strategies

Abstract

A set of two-cylinder engine concepts utilizing a supercharger and piston-compounding or turbine-compounding were compared to a supercharged, non-compounded engine modeled with a consistent methodology. The goals of this simulation were to utilize energy that otherwise would be bypassed around the turbine side of a turbocharger and redirect it to the crankshaft. Following previous modeling work on a different piston-compounded engine, the gains in performance and efficiency for these concepts were thoroughly analyzed to provide insight into the magnitudes and responsible mechanisms. It was found that the second expansion process from exhaust-compounding was able to significantly improve engine performance at moderate to high loads, but the level of benefits and low-load performance were highly dependent on the compounding technique.

Low-load expander deactivation studies for a light-duty single-shaft piston-compounded engine

“…The contribution of the expander cylinder to the brake torque at each fueling rate for all the deactivation methods are displayed to the left in Figure 5. As discovered in previous works, 1,2 at low loads, the piston-compounding presents a liability since the motion of the piston driven by the crankshaft is not easily stopped, especially when taking into consideration the engine balancing. The brake torque metric plotted here also includes effects of the expander on the power cylinder pumping loop when the expander is active and is computed as the difference between each method and a hypothetical supercharged two-cylinder engine without expander, running under the same boundary conditions and fueling rates.…”

“…The one-dimensional, analytical piston DCDE engine model that was developed in GT Power and used in prior work 1,2 was used as the basis for this modeling effort. Minor adjustments were made to the cylinder and valve geometries from those previous works to better reflect the experimental hardware that was being designed alongside and with the help of the modeling work.…”

“…Therefore, excess power that could be generated by the turbine through compounding cannot affect the crank work except through the balance of intake and exhaust pressures on the engines’ pumping loop. 1 Alternative single-shaft DCDE engine architectures including exhaust compounding were investigated in previous work, where it was determined that a piston-compounded, supercharged architecture could recover substantial exhaust energy to improve brake efficiency. 2…”

“…1 Alternative single-shaft DCDE engine architectures including exhaust compounding were investigated in previous work, where it was determined that a piston-compounded, supercharged architecture could recover substantial exhaust energy to improve brake efficiency. 2…”

“…The piston-compounded engine is based on the optimized configuration from previous work, 1 as shown in Figure 1. It utilizes a pair of conventional four-stroke “power” cylinders completing a cycle over 720° at 360° phasing intervals which alternately exhaust into a piston expander.…”