Abstract A high temperature heat exchanger has been developed for application in a Rankine cycle. (Organic) Rankine Cycle technology is considered for exhaust Waste Heat Recovery from heavy-duty vehicles and other high power applications. The developed exhaust evaporator has a modular and durable design and can operate at high temperature and pressure range. The design has been tested and validated and has been certified according to European pressure equipment and German AD 2000 directives. Units have been accumulating in-field operating hours since 2007 without failure. The modular design allows to tailor an evaporator for specific applications. This process is supported by a developed dimensioning tool and simulation models.69803

Keywords Waste heat recovery Rankine cycle Heat exchanger Evaporator Simulation

1 Introduction

The past decade has seen an increased attention for the fuel consumption of internal combustion engines. This attention is caused by an increased awareness for sustainability, CO2 emissions, fossil fuel energy security and increasing oil prices. This trend is also reflected in new legislative documents affecting internal combustion engines in passenger cars and commercial vehicles (e.g. [1]). Where up till recently attention was geared towards reducing pollutants, the focus is shifting to the reduction of fuel consumption and CO2 emissions.

J. Fischer-Wolfarth and G. Meyer (eds.), Advanced Microsystems for Automotive Applications 2013, Lecture Notes in Mobility, DOI:  10.1007/978-3-319-00476-1_28,

© Springer International Publishing Switzerland 2013

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The larger internal combustion engines consume a considerable amount of fuel. For that reason their efficiency has received continuous development over the years and their fuel efficiency has been kept as low as economically viable within the set limits for emissions. To further reduce the CO2 emissions for these engines new technologies are considered. One candidate technology is the application of exhaust Waste Heat Recovery (WHR) through the application of a Rankine Cycle for a heat to power application (H2P). While also investigated for passenger car applications [2], this technology is particularly suited for larger internal combustion engines running at considerable average loads, such as in long-haul heavy-duty trucks and Combined Heat and Power (CHP) generator applications. In a Rankine Cycle (exhaust) heat that is otherwise wasted is used to generate steam in an evaporator (Fig. 1). Superheated steam is fed to an expander device that uses the steam expansion to generate mechanical power. After expansion the stream is fed to a condenser which condenses the stream to liquid water stored in a

tank. A pump is used to feed the water to the evaporator.

Numerous variants on this cycle exist. The heat recovery cycle may be better compatible with the waste heat source temperature if a working fluid other than water is used. This is for example the case for exhaust Waste Heat Recovery for heavy-duty trucks. Various working fluids are considered for these applications such as ethanol and refrigerant R245fa [3]. With this choice for working fluid the cycle is called an Organic Rankine Cycle.

Also, different options exist for the expander device [3]. It may for instance be of a piston machine, scroll expander or turbine type. Depending on the application the generated power may be fed to the engine crankshaft or converted to electricity.

Expander

Fig. 1 Rankine cycle for exhaust waste heat recovery

Specifically for heavy-duty diesel truck application there are generally two waste heat sources of consideration. One is offered by the main exhaust gas stream. The other source is the heat of the exhaust gas that is recirculated to reduce Nitrogen Oxide emissions. This Exhaust Gas Recirculation (EGR) stream is nor- mally cooled by a specific EGR cooler, but may be replaced by an EGR evaporator for Waste Heat Recovery. Experimental studies have already demonstrated fuel savings up to 6 % for systems utilising both sources [4, 5].