Throttle loss recovery using a variable geometry turbine

Two of the most pressing challenges of the automotive sector are reduction of fuel consumption and corresponding emission of greenhouse gases, especially when taking into account the growing degree of luxury in modern passenger cars, which increases the auxiliary load on the engine. Preferably, this increase in auxiliary load is compensated by the recovery of waste energy. To accomplish this, a technology called WEDACS (Waste Energy Driven Air Conditioning System) is being developed to recover throttling losses. WEDACS uses a turbine to induce provide the engine with the same air mass flow rate as a throttle valve while producing mechanical energy and cold air. An alternator coupled to this turbine converts mechanical energy into electrical energy and the cold air is used to cool A/C fluid. This way the load of both the engine-mounted alternator and A/C compressor is reduced or eliminated, resulting in higher efficiency. A previous paper provides a proof of principle, using a turbine from a turbocharger, but also discusses a challenge in the form of a limited operating range. The present paper focuses on addressing this challenge. To expand the control range of the engine, a turbocharger with variable nozzle turbine is used. Due to limitations in the variable nozzle mechanism, the range is limited to higher engine powers. It is shown that between 50 W and 1.3 kW of energy can be recovered from a 2-liter engine, depending on the operating point. A second turbocharger's variable nozzle mechanism is adapted to enable control of a 2-liter engine from idle to about 50% engine power. With decreasing engine power, the energy recovery efficiency eventually drops to zero. The root cause for this is identified and an attempt is made to improve efficiency. Finally the drive cycle model from the previous paper is expanded and a new drive cycle simulation shows a fuel consumption improvement over the NEDC of about 5 to 8% for a mid-sized passenger car with a 2-liter engine