Air Compressor



Metrics Table



METRIC SUB-METRIC UNITS RATING DATA SECTOR
Technology Accessibility Compatibility with existing consumer technologies 0-4 1-4 depends on application all
Number of companies selling the technology number 0-2 depends on application all
Probability of market co-existence with current (competing) technology 0-4 2-4 depends on application all
Global Environmental Impact GHG- emissions at full load g / kg fuel - 0 all
GHG- emissions at part load g / kg fuel - 0 all
Local Environmental Impact Air quality impact (consider NOx, PM, CO, NMHC) 0-4 4 - all
Noise or perception of noise from the technology (SPL, loudness,etc.) dB(A), sone - >60 dB @ 1m Transport
- N/A other
Design / product appearance impact 0-4 N/A depends on application all
Efficiency Part load efficiency of technology % - 50-77% Transport
- >55% other
Full load efficiency of technology % - 34-75% Transport
- >60% other
Efficiency of auxiliary components % - N/A all
Capacity & Availability Capacity to meet users needs (e.g. Performance and acceleration of vehicle) 0-4 N/A - all
Number of hours per year during which technology is available hours/year - N/A all
Durability of technology hours - N/A all
Cost
(click here for more datails) 		Capital investment for technology EUR - 865 (90 g/s airflow rate)[1] all
Cost of ownership for consumers (e.g. Maintenance) EUR / year - N/A all
Cost per unit of energy from technology EUR / kW - 2000-3000 $/kW (H2 compressed to 215 atm)[2] all
Safety Technology breakdown (including misuse) no. / year - N/A all
Severity of failure 0-4 N/A - all




Summary

Pressure plays an important role on the electrical output of the stack (fuel cells have better efficiency and power density when operating at air pressure higher than ambient) and on stack's water balance (at the same temperature of moist air, water quality of air at ambient pressure is higher than that of pressurized air).

On the other hand it is known as well that an increase of the operating pressure has a deep impact on required power to compress the air. Most of on-going activities on cathode side have the focus to evaluate the best fuel cell system's operating pressure range in terms both of fuel cell system efficiency and water balance.

Super and turbo charging are quite common operation in automotive field, but it must be noted that those machines are either mechanically or exhaust gases driven and that the internal combustion engine requirements, in terms of pressure and flow rates, are not the same as of a fuel cell system.

Compressors are usually classified into two classes, according to the physical way the machine transfers the energy to the air:
  • Dynamic (turbo) - centrifugal, axial
  • Positive displacement
Dynamic Compressors are rotary continuous - flow machines in which the rapidly rotating element accelerates the air as it passes through the element, converting the velocity head into pressure, partially in the rotating element and partially in stationary diffuses or blades.

Positive displacement units are those in which successive volumes of air are confined within a closed space and elevated to a high pressure .The capacity of a positive displacement compressor varies marginally with the working pressure.

Positive displacement ones can be further classified into two types, depending on principles they use to deliver air at high pressure:
  • Reciprocating compressor (alternative)
  • Rotary compressor
A general sketch of different categories of compressors is given in the figure below.

Classification of compressors
A centrifugal turbo compressor is, in general, a superior machine in terms of efficiency, and therefore offers the most promising effect on the whole system energy balance. Positive displacement compressors, on the other hand, offer more flexible pressure ratio at low fuel cell loads, which is an important issue with PEM fuel cell systems, since they don't suffer surge issues.A comparison of the efficiencies and pressure range for different compressor types is shown in figure below.


Rating of different compressor types for PEM fuel cell applications


Characteristics of a dynamic compressor

Characteristic of a variable displacement compressor
Some of the companies selling different compressor types are the Aerzener Maschinenfabrik GmbH, Borg Warner Turbo Systems, IHI and others.

The noise emitted from a compressor is greater than 60dB at 1m (see figure below, EN ISO 3744 measurement of a screw compressor). For transport applications the part and full load efficiencies of a compressor are 50-70% and 34-75% respectively. For other applications the part and full load efficiencies are greater than 55% and 60% respectively.


Sound pressure measurement (EN ISO 3744) of a screw compressor
Some compressors for use with fuel cell incorporate the humidifier. However, little information about the state-of-the-art of these types have been collected so far.


Key Issues

Air compressor is a critical device in fuel cell systems, particularly for transport application. Development of this component must take into account also particular issues due to association with a stack
  • Low parasitic consumption (efficiency improvement): since compressor is the device with the highest power consumption from fuel cell and therefore it heavily affects fuel cell system efficiency
  • Large turn down ratio: Compressor should operate over a wide range of air flow rate
  • High dynamic response to satisfy requirements due to a vehicle acceleration
  • Noise reduction
  • Reduce volume and weight to completely fulfil automotive requirements
  • Reduce cost directly linked to mass production of device; cost reduction must involve fluid dynamic machine and electric/electronic section
  • Integration into the whole cathode side, taking into consideration stack's requirements in terms of temperature and humidification
  • Air at the outlet of compressor should be oil free: Presence of contaminants in the air at stack inlet may decrease stack's performances or, at least, damage it.



Data Lacking

More information relating to cost, safety, durability and controlability is desirable.




References

  • S. Pischinger, J. Ogrzewalla, C. Schönfelder
    Optimierung von Luftversorgungseinheiten für
    Brennstoffzellensysteme in Fahrzeugantrieben
    VDI-Berichte Nr. 1975, 2006
  • D. Stolten
    Grundlagen und Technik der BrennstoffzellenRWTH Aachen
  • C. Mohrdieck, A. Docter
    Technical Status and Outlook for Fuel Cell Drive Systems at DaimlerChrysler
    VDI-Berichte Nr. 1975, 2006
  • J. Haubrock , G. Heideck , Z. Styczynski
    Electrical Efficiency Losses Occurred by the Air Compressor for PEMFC
    WHEC 16, Lyon France, 13 - 16 June 2006
  • S. Pischinger and C. Schönfelder, W. Bornscheuer, H. Kindl, A. Wiartalla
    Integrated Air Supply and Humidification Concepts for Fuel Cell Systems
    Sae Technical Paper Series 2001-01-0233
  • E.J. Carlson, P. Kopf et al.
    Cost Analysis of PEM Fuel Cell Systems for transportation
    National Renewable Energy Laboratory, 2005
  • D.R. Simbeck, E. Chang
    Hydrogen Supply: Cost Estimate for Hydrogen Pathways - Scoping Analysis
    National Renewable Energy Laboratory, Golden (Colorado), USA, 2002

Notes

  1. ↑ Honeywell Fuel Cell Turbo-Compressor with Mixed-Flow Compressor and VNT® Variable Nozzle Turbine including electronics
    Source:E.J. Carlson, P. Kopf et al., Cost Analysis of PEM Fuel Cell Systems for transportation, National Renewable Energy Laboratory, 2005
  2. ↑ Simbeck, D.R., Chang, E., Hydrogen Supply: Cost Estimate for Hydrogen Pathways – Scoping Analysis, National Renewable Energy Laboratory, Golden (Colorado), USA, 2002
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