Hydrogen Engines are in focus to meet the future legislations concerning our environment.
Prof. Eichlseder (Univ. Graz) published new measurements last year (2020) which showed the need for a sequential turbo charging concept to get an optimum out of the used hydrogen engine. The new Pressure Wave Supercharger (PWS) Comprex™ fulfils these needs perfectly due to a sequential charging system by design and even more, like an included engine break and power turbine. Seems like it would have been specially developed for this application. See also [16].
The new concept will be shown in this paper and why it fits perfect to hydrogen Engines.
Also, the new possibilities regarding the exhaust gas treatment to reach ultra-low emissions and the response and efficiency of the Comprex™ System will be discussed.

Hydrogen Engines are in focus to meet the future legislations concerning our environment.
Prof. Eichlseder (Univ. Graz) published new measurements last year (2020) which showed
the need for a sequential turbo charging concept to get an optimum out of the used hydrogen
engine. The new Pressure Wave Supercharger (PWS) Comprex™ fulfils these needs
perfectly due to a sequential charging system by design and even more, like an included
engine break and power turbine. Seems like it would have been specially developed for this
application. See also [16].
The new concept will be shown in this paper and why it fits perfect to hydrogen Engines.
Also, the new possibilities regarding the exhaust gas treatment to reach ultra-low emissions
and the response and efficiency of the Comprex™ System will be discussed.

To increase the efficiency of a natural gas engine, the use of a Miller camshaft was analysed. To avoid a decline in the low-end torque and also in the transient response, a pressure wave super- charger (ComprexTM) was compared to the conventional single-stage turbocharger. The analyses for this conceptual comparison were performed experimentally, and the data were then used to run simulations of driving cycles for light commercial vehicles. A torque increase of 49% resulted at 1250 rpm when the ComprexTM was used in combination with a Miller camshaft. Despite the Miller camshaft, the ComprexTM transient response was still faster than the turbocharged engine. Using the same camshaft, the turbocharged engine took 2.5-times as long to reach the same torque. Water injection was used to increase the peak power output while respecting the temperature limitations. As the ComprexTM enables engine braking by design, we show that the use of friction brakes was reduced by two-thirds. Finally, a six-times faster catalyst warmup and an up to 90 ◦C higher exhaust gas temperature at the three-way catalytic converter added to the benefits of using the ComprexTM supercharger. The known drawbacks of the ComprexTM superchargers were solved due to a complete redesign of the machine, which is described in detail.

Info Flyer 2019 ATK (Aufladetechnische Konferenz Dresden)

Pressure wave superchargers (Figure 1) use pressure waves of the exhaust gases to compress fresh air in the cells of the rotor. The rotor turns, driven by electric motor, so this process can be synchronized. Due to the principle that exhaust gases are compressing fresh air in direct contact, the rotor speed can also be used to control exhaust gas recirculation. In engines working at λ=1 principle the three-way-catalyst needs to be located before boosting device, which can have a positive impact on its performance, for example during cold start.

How does a Pressure Wave Supercharger work and why use it?

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Abstract. Born more than a century ago, the concept of exploiting the pressure wave phenomenon has evolved with rather small steps, experiencing an accelerated progress over the past decades. This paper aims an overview on the researchers’ results over time regarding the pressure wave technology and its applications, pointing out on the internal combustion engine’s supercharging application.
This review complements the past reports on the subject, presenting the evolution of the concept and technology, as well as the researcher’s efforts on solving the specific shortcomings of this pressure wave technology. Undoubtedly, the pressure wave rotors have been a research goal over the years. At first, most of the researches were experimental and the theoretical calculations required to improve the technology were too arduous. Recently, new computer software dedicated to accurate simulation of the processes governing the wave rotor operation, altogether with modern experimental measurement nstruments and well-developed diagnostic techniques have opened wide possibilities to innovate the pressure wave supercharging technology.
This paper also highlights the challenges that specialists still have to overcome and aspects to become future preoccupations and research directions.

As small, Remotely Piloted Aircraft become more prevalent as aerial observation
platforms in the modern era, there will continue to be a desire to improve their capabilities.
The lowered pressures associated with high altitude have an adverse impact on the
performance of the small engines that are commonly used to propel small aircraft. The
most desirable method of recovering the performance lost as a result of engine operation
at high altitude is the integration of a forced induction device. Due to its unique
characteristics, a special type of wave rotor called a Pressure Wave Supercharger has the
potential to avoid many scaling-related losses, allowing it to operate efficiently as a forced
induction device for small engines. This thesis outlines the successful design and
computational simulations performed in the development of a Pressure Wave Supercharger
for a 95 cc Brison engine. A NASA quasi one-dimensional CFD code was used to produce
computational predictions for the performance of a Comprex® Pressure Wave
Supercharger and compare these predictions against the measured performance. This code
was then used to design a scaled down Pressure Wave Supercharger for use on the 95 cc
Brison. This design was modeled using Computer Aided Design and the parts were
manufactured. A test rig was also designed for the purpose of testing the scaled Pressure
Wave Supercharger. This device will improve the performance of small two-stroke engines
flying at high altitudes by boosting the intake manifold pressure to one standard atmosphere
or better. This will allow small unmanned aerial systems operated by the Air Force to
function at higher altitudes, thus improving their capabilities and mission effectiveness.

The objective of this paper is to provide a succinct review of past and current research in
developing wave rotor technology. This technology has shown unique capabilities to
enhance the performance and operating characteristics of a variety of engines and ma-
chinery utilizing thermodynamic cycles. Although there have been a variety of applica-
tions in the past, this technology is not yet widely used and is barely known to engineers.
Here, an attempt is made to summarize both the previously reported work in the literature
and ongoing efforts around the world. The paper covers a wide range of wave rotor
applications including the early attempts to use wave rotors, its successful commercial-
ization as superchargers for car engines, research on gas turbine topping, and other
developments. The review also pays close attention to more recent efforts: utilization of
such devices in pressure-gain combustors, ultra-micro gas turbines, and water refrigera-
tion systems, highlighting possible further efforts on this topic. Observations and lessons
learnt from experimental studies, numerical simulations, analytical approaches, and
other design and analysis tools are presented.
DOI: 10.1115/1.2204628

The Comprex supercharger compresses air by direct transmission of energy from an expanding gas tilizing compression and expansion waves. The name Comprex is a contraction of Compression-Expander. Although the phenomena of nonsteady flow have been studied extensively in connection with explosions, diesel fuel injection, railway airbrakes, water hammer, safety equipment in hydraulic power stations, and so on, the use of these effects in gases is relatively new. This paper deals with the Comprex as applied to supercharging of internal-combustion engines. It explains the principle of operation, describes the design and discusses the particular operational characteristics as a supercharger for a 4-cycle diesel engine. It should be remembered that this is only one of many applications of a broad and unexploited field.