Abstract:In this paper we demonstrate the potential of combining electric hybridization with a dual-fuel natural gas-Diesel engine. We show that carbon dioxide emissions can be reduced to 43 gram per kilometer with a subcompact car on the New European Driving Cycle (NEDC). The vehicle is operated in charge-sustaining mode, which means that all energy is provided by the fuel. The result is obtained by hardware-in-the-loop experiments where the engine is operated on a test bench while the rest of the powertrain as well as the vehicle are simulated. By static engine measurements we demonstrate that the natural gas-Diesel engine reaches efficiencies of up to 39.5%. The engine is operated lean at low loads with low engine out nitrogen oxide emissions such that no nitrogen oxide aftertreatment is necessary. At medium to high loads the engine is operated stoichiometrically, which enables the use of a cost-efficient three-way catalytic converter. By vehicle emulation of a non-hybrid vehicle on the Worldwide harmonized Light vehicles Test Procedure (WLTP), we demonstrate that transient operation of the natural gas-Diesel engine is also possible, thus enabling a non-hybridized powertrain as well.

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Downsizing and turbocharging is a common approach to improve the fuel economy of spark-ignited combustion engines. However, the inherent turbo lag results in a loss of driveability. In-cylinder boosting is an effective way to eliminate this problem. In the first part of this two-part study, a deactivatable camshaft-driven valve controlling the air mass flow from a pressurised air-tank directly into the cylinder was proposed as the main actuator of such a system, where also a model-based design procedure was demonstrated. In this paper, the torque control during the turbo lag compensation is discussed. The control is complicated by the limited variability of the mechanical valve-train. This limited variability gives rise to a trade-off between fuel and pressurised air consumption. However, the proposed control strategy minimising the consumption of pressurised air (thereby minimising the space required for the pressurised air tank), causes only a small penalty in fuel consumption. This air-mass-based control strategy actuating the throttle, ignition timing and boost mode timing is analysed in simulation and then verified experimentally in various operating conditions.

In this paper, we present an analysis of the optimal burn rate in an internal combustion engine (ICE) considering pressure gradient, maximum pressure, and knocking. A zero-dimensional model with heat losses is used for that purpose. The working fluids are assumed to behave like ideal gases with temperature dependent gas properties. In the first part, it is assumed that the burn rate can be arbitrarily chosen at every time instance in order to maximize the mechanical work. This leads to an optimal control problem with constraints. In the second part, a Vibe type burn rate is assumed, where the center of combustion, the duration and the form factor can be chosen in order to maximize the mechanical work. This Vibe type burn rate is finally compared with the arbitrary combustion as the benchmark in order to evaluate the potential of the more realistic burn shape.