In this paper, the novel machine type of an electric air compressor (EAC) for fuel cell applications is investigated and simulated using a Pseudo Bond Graph (PBG) approach. Initially, the system along with its miscellaenous components is derived in the Pseudo Bond Graph notation. Subsequently, the multiphysical connections of fluid, thermal and electrical domains are highlighted. In addition, a derivation for an extended definition of the Pseudo Bond Graph theory’s inertia I element is presented. In contrast to the previous formulation, it takes into account the effects of compressibility which were previously neglected. The simulations are carried out using in-house simulation tool ASTOR (AircraftEngine Simulation for Transient Operation Research) and feature different transient acceleration and deceleration manoeuvres with varying manoeuvre duration. It is shown that manoeuvre duration significantly influences transient performance such as the surge margin which is found to decrease by up to 9% in comparison to the steady operating line. In addition, deceleration is identified as the most critical operating condition.

Ammonia is expected to be a hydrogen carrier that has potential as a carbon-free fuel. Ammonia is known as a nonignitable fuel, and it is not easy to hold ammonia flames under atmospheric conditions. A demonstration test with the aim of showing the potential of ammonia-fired power plants was conducted using a micro gas turbine. A 50-kW-class turbine system firing kerosene was selected as a base model. More than 40 kW of power generation was achieved by firing ammonia gas or a mixture of ammonia and methane by modifying the combustor, the fuel control device, and the gas turbine startup sequence. The prototype bifuel combustor is a swirl combustor employing a non-premixed flame and a decreased air flow rate near a gas fuel injector for flame holding. Ammonia combustion in the prototype bifuel combustor was enhanced by supplying hot combustion air and by modifying the air inlets. However, the exhaust gases from the ammonia flames had high NOx concentrations. NOx removal equipment using selective catalytic reduction can reduce NOx emission levels to below 10 ppm from more than 1000 ppm (converted value of NOx to 15% O 2 ) as already reported. However, downsizing of NOx removal equipment should be achieved for practical use. Therefore, a low NOx combustor was developed. As the first step of the development of the combustor, flame observation in the gas turbine combustor was tried. Although the observation area was limited, an inhomogeneous swirling orange flame of ammonia gas was observed. Then, a combustor test rig was prepared for a detailed observation of ammonia flame under various combustion conditions. The combustor test rig used a regenerative heat exchanger for heating combustion air, and it used an orifice for pressure drop instead of a turbine. Combustion air and cooling air were supplied from two air compressors. At startup of the combustor test rig, a spark plug was used to ignite non-premixed methane and air. After heating the regenerative heat exchanger, ammonia gas was supplied to the combustor instead of methane gas. The exhaust gases from the combustor were analyzed using FTIR (Fourier transform infrared spectroscopy) under various conditions, such as methane firing, methane–ammonia firing, and ammonia firing. Although there are several concepts for NOx reduction, a rich–lean combustion method was applied first for ammonia firing. The rich–lean combustor modified from the prototype bifuel combustor also could burn ammonia well in cases of both methane–ammonia firing and ammonia firing. The rich–lean combustor succeeded in reducing NOx emission from methane–ammonia combustion to half the value measured in the case of the prototype bifuel combustor.

The Heron Fan is a new concept of a fuel powered jet engine that does not utilize a conventional core engine. The fan, a single axial compressor of high diameter, creates thrust, similar to a turbofan. Its blades are hollow with inner channels to transport the core air from the hub to the tip, inducing radial compression. The combustion chamber is located in the casing region, either integrated in the blades or in an external ring. After burning, the core air is returned to the blades and is blown out through an expansion device with a large component in circumferential direction. This propels the fan in the opposite direction. The expansion device may be realized by nozzles integrated in the blade trailing edge or by turbine stages integrated in the blade tip region. Subsequently, the core air mixes with the bypass air, which passes the fan axially, and ejects through the main nozzle, producing thrust. To achieve higher compression ratios, it is possible to install core air compressor stages ahead of the fan. The main purpose of this concept is to reduce weight and complexity of the engine, leading to lower production and operating costs. This is achieved by simplifying the engine architecture, integrating the functions and shortening some of the components. In particular, the core engine has been rearranged, thus eliminating the second and in some cases the third shaft. Further, the complete expansion and parts of the compression have been integrated in the fan blade. To assess the aero-thermodynamic parameters, a preliminary cycle analysis has been done, where the most influential parameters were varied. The results show, that the above listed benefits can be achieved while maintaining an efficiency comparable to conventional turbofans. Further, a feasibility study in terms of geometry, internal flow, component implementation and installation has been done, in order to qualify the concept and to identify the most critical aspects. To incorporate the corresponding thoughts and results, as well as to find and eliminate conceptual conflicts and opposing trends, a CAD model has been generated. Overall, the results are sound and encouraging, hence justifying future investigations. However, the Heron Fan concept also brings structural, thermal and aerodynamic challenges which are illustrated and briefly discussed, but still need detailed investigation.

Helium compressor is a main component of high temperature gas reactor (HTGR) helium power conversion unit, and its performance has significant effects on the power output and cycle efficiency. In this paper, the flow loss analysis of highly loaded axial helium compressor is carried out using a computational fluid dynamics (CFD) program at both design and off-design point. To understand the loss mechanism of the highly loaded helium compressor, special attention is paid to the tip clearance loss, profile loss and the end wall loss. As is well-known, when increasing the backpressure, the specific power and adverse pressure gradient of general air compressor cascade increase as well. But the specific power and adverse pressure gradient of the highly loaded design helium compressor in this paper will decrease with the backpressure increasing due to the new velocity triangle. So the loss characteristics of the highly loaded helium compressor are different from that of air compressor. From the three-dimensional viscous numerical results, the profile loss is the most important loss source of the highly loaded helium compressor. The proportion of the highly loaded helium compressor profile loss is more than 50%.

The air supply system plays a key role for Proton Exchange Membrane (PEM) fuel cells. The performance of PEM fuel cells can be significantly improved by increasing the air supply pressure and air stoichiometric ratio. However, the increased electrical power consumption of the conventional motor driven air compressor operated at higher pressure would reduce the overall efficiency of the PEM fuel cell system. This paper proposes three novel air supply systems in which the compressor is driven by the waste heat recovered by the Organic Rankine Cycle (ORC) from the stack cooling water and the exhaust gas. The influences of air supply pressure and air stoichiometric ratio on the PEM fuel cell performance and exhaust gas are investigated through the fuel cell stack model. The performance analysis of the air supply system is carried out using a thermodynamic simulation model. And the proposed three air systems are compared to an air system driven by the exhaust gas and the assisted motor. Results show that both the air pressure and air stoichiometric ratio are improved significantly. The gross output electric power and the net efficiency of the PEM fuel cells are also improved greatly because of higher operating pressure and the elimination of the compressor power consumption. Among the 3 proposed air systems, the air system which has a self-circulation to maintain the stack temperature has the best performance and is most stable in operation.

In conjunction with the SunShot program to develop a supercritical CO 2 turbine expander, an air dynamometer was developed to absorb the power of the SCO 2 turbine during development testing. The dynamometer is unique in that it is directly mounted to the shaft of the turbine expander replacing the associated compressor coupling during the test campaign. It is able to replicate both the load of the compressor as well as the rotordynamic qualities of the compressor coupling all without the need for additional bearings, casing, or larger skid. The dynamometer consists of a single-stage centrifugal air compressor ingesting ambient air. To maximize turn-down and minimize weight, the impeller diameter and flow coefficient were optimized along with the design of the loop throttle valves. The detailed aerodynamic, rotordynamic, and mechanical design for the dynamometer is presented. The aerodynamic methodology to minimize unsteady forces transmitted to the turbine will also be reviewed.

Gas Turbines (GT), like other prime movers, experience wear and tear over time, resulting in decreases in available power and efficiency. Further decreases in power and efficiency can result from erosion and fouling caused by the airborne impurities the engine breathes in. To counteract these decreases in power and efficiency, it is standard procedure to ‘wash’ the engine from time to time. In compressor stations on gas transmission systems, engine washes are performed off-line and are scheduled in such intervals to optimize the maintenance procedure. This optimization requires accurate prediction of the performance degradation of the engine over time. A previous paper demonstrated a methodology for evaluating various components of the GT gas path, in particular the air compressor side of the engine since it is most prone to fouling and degradation. This methodology combines Gas Path Analysis (GPA) to evaluate the thermodynamic parameters over the engine cycle followed by parameter estimation based on the Bayesian Error-in-Variable Model (EVM) to filter the data of possible noise due to measurement errors. The methodology quantifies the engine-performance degradation over time, and indicates the effectiveness of each engine wash. In the present paper, the methodology was extended to assess both recoverable and un-recoverable degradations of five gas turbine engines employed on TransCanada’s pipeline system in Canada. These engines are: three GE LM2500+, one RR RB211-24G, and one GE LM1600 gas turbines. Hourly data were collected over the past four years, and engine health parameters were extracted to delineate the respective engine degradations. The impacts of engine loading, site air quality conditions and site elevation on engine-air-compressor isentropic efficiency are compared between the five engines.

Studies were made of the feasibility of simulating acoustical and aerodynamic characteristics of a full-scale axial-flow air compressor with a scale model operating in Freon in a closed-loop system. Correlation was attained between model and prototype for both acoustical and aerodynamic performance. Agreement was obtained with a previously published generalized acoustic prediction curve; and a tentative acoustic scaling law was developed which permits rapid prediction of full-scale sound power levels from measurements of the sound power levels produced by a model.

The object of the experiment discussed in this paper was to determine (to a preliminary degree) the extent to which the operating range could be extended and the surging characteristics varied by the combination of acoustic suppressors with an air compressor, such as by connection to the discharge duct system of the air compressor.

This paper presents information on the NREC core engine development program. The subject engine is a 100-hp, two-shaft gas turbine that is the low-power end of a family of engines up to 500 hp, both nonregenerative and regenerative. The major goal of the program has been the development of a low-cost small gas turbine engine (less than $5/hp to produce in quantities of 15,000/yr). Other objectives include low emissions (meeting the anticipated EPA standards for the markets of interest), relatively high performance (design point SFC = 0.7 for the simple-cycle engine and 0.4 for the regenerative version), and relatively long life (10,000-hr life at design power and a minimum service period of 500 hr). Items specifically covered in this paper include the following: ( a ) A description of the core engine concept. Frame size, regenerative, recuperative, and air compressor versions are discussed. ( b ) A technical description of the core engine concept. The salient low-cost features are identified. ( c ) The development program results. Some of the engine performance and manufacturing cost analysis results are given.

Detroit Diesel Allison (DDA) Division of General Motors Corporation, has developed a 7000-shp class gas turbine engine for industrial use. The engine uses proven modern technology which results in low-fuel consumption over a wide range of power and a compact installation envelope. Approximately 5000 hr of performance and endurance testing have been accumulated to date. Testing is continuing at DDA and the first-field installation was completed in September 1977 in a stationary air compressor application. It is anticipated that 10,000 hr of engine test experience will be gained prior to production unit availability in 1978. This paper discusses the mechanical arrangement, performance, control system, installation and maintenance features, and status of the Model 570 engine.

An experimental investigation concerning the optimum relative velocity distribution within impellers, the optimum diffusion ratio of vaned diffusers and the optimum circumferential area distribution, sectional shape of scrolls was carried out using high specific speed shrouded impellers with backward leaning blades. A performance design procedure based on loss analysis and quasi-three-dimensional flow analysis was also developed and modified by introducing experimental results. The design procedure was applied to a 7900-kw four-stage air compressor to demonstrate the usefulness. Field test results of the complete machine showed that the maximum isothermal efficiency was 75 percent with the pressure ratio of 5.96 and the flow rate of 29.3 m 3 /s.

Two recent applications for a heavy duty industrial gas turbine engine are discussed. The principal design requirements for both cases are compared and the design changes necessary to meet the requirements are illustrated. In the case of a main pipeline compressor driver, the need for high thermal efficiency over a wide range of loads is met by use of a regenerative cycle and by reprogramming the loading sequence. Long term step increases in engine capability were provided by incorporating a unique engine convertability feature. In the case of a process air compressor driver with exhaust heat recovery, the engine exhaust temperature and gas flow imposed constraints on engine capability during high ambient temperature operation and on engine operation at low ambient temperature conditions. The constraints were met by the use of steam injection to augment power at high ambient temperature conditions and by the use of variable inlet guide vanes to control exhaust flow at the low temperatures.

Modifying a simple-cycle gas turbine to include heat exchangers can improve its thermal efficiency significantly (as much as 20%). Advanced regenerative and intercooled regenerative gas turbines for marine application have recently been the subjects of numerous studies, most of which have shown that lower fuel comsumption can be achieved by adding heat exchangers to existing simple-cycle gas turbines. Additional improvements in thermal efficiency are available by increasing the efficiency of the turbomachinery itself, particularly that of the gas turbine’s air compressor. Studies by Caterpillar Tractor Company and Solar Turbines Incorporated on a recuperated, variable-geometry gas turbine indicate an additional 8 to 10% improvement in thermal efficiency is possible when an improved higher efficiency compressor is included in the gas turbine modification. During these studies a novel (Axi-Fuge) compressor was devised. This paper discusses the Axi-Fuge concept, its origin, design criteria and approach, and some test results.

In this Steam Injected Gas turbine cycle, maximum steam is raised with exhaust heat at the highest practical pressure for expansion in a back pressure steam turbine before injection into the gas turbine combustor. Additional steam is raised at lower pressure and injected into the combustor, to effect more complete recovery of heat. The back pressure steam turbine drives a topping air compressor which raises the gas cycle pressure ratio. This allows the standard gas turbine blading to accommodate the additional steam flow because of the higher pressure and density of the gas.

Test results are presented comparing the aerodynamic performance of single stage centrifugal compressors with thin flat plate, low solidity vaned diffusers to conventional thin vaned diffusers. The test data were acquired from a low Mach number process gas compressor and a high Mach number industrial air compressor. The data are all normalized relative to baseline vaneless diffuser results. Performance parameters of stability, head rise to surge, overload flow margin, and stage efficiency are compared. The low solidity vane inlet incidence angle is shown to be an important design parameter that influences both compressor operating range and efficiency.

Software commonly used to predict Aeroengine performance has been adapted for the design point simulation of two large industrial compressor sets. A NO x gas compressor and an air compressor on a common shaft driven by a steam turbine and a tail gas turbine are modelled accurately after the inclusion of both exothermic and endothermic reactions in the NO x gas compressor. Experiment and theory agree to within 1.5%. Results for the simulation of a three spool Ammonia Synthesis compressor with a deliver pressure of 207 bar agree to within 1% of experimental data. Since complex gas mixtures were used, Mollier diagrams or Compressibility factor techniques were not used and, instead, Departure Function theory was adopted to accommodate the real gas behaviour found at the high pressure.

In Compressed Air Energy Storage (CAES) systems, off-peak electric energy is consumed by air compressors that charge CAES reservoirs. During peak load hours, air released from the CAES reservoir expands, producing electric power. Two novel CAES systems, improving their reliability and efficiency, are introduced. The first system is the CAES Plant Integrated with a Gas Turbine (CAESIGT), in which 40 percent of the power output is produced by a standard gas turbine, and 60 percent by an air expander utilizing compressed air that is preheated by the exhaust gases of the gas turbine. For certain initial parameters of the compressed air, its temperature after expansion becomes lower than the ambient temperature. This cold air can be used as a source for refrigeration of the gas turbine inlet air and for other purposes. In the CAES system of the second type, multistage expansion of compressed air is applied. Reheating air between expander stages is provided either by refrigerated substances, by heat sources from surroundings, or by non fuel heat sources such as the waste heat from industry, solar ponds, etc. Thermodynamic and economic analyses of the novel CAES systems are carried out.

An unusual centrifugal impeller disk failure has been encountered in one of the stages of a multistage air compressor. The failure occurred when a triangular piece of metal separated from the disk at the rim of the impeller disk. Stress analyses show that the steady hoop stresses at the rim were very low. Metallurgical observations indicate that the failure was caused by high cycle fatigue in cast 17-4 PH steel. A modal analysis shows that the failure can be explained by a resonance condition. The excitation of the backward rotating tangential nodal pattern by the stationary vaned diffusers just downstream of the impeller rim causes this resonance condition. Avoiding the resonance condition by changing the number of diffuser vanes has eliminated the failures.

This paper investigates the performance problem of a large capacity multistage centrifugal air compressor when operated continuously for an extended period of time without overhauling. The compressor flow constitutes fifty percent of the plant production and plays a critical role in meeting the annual contract capacity and can not tolerate performance instability due to high intercooler temperatures, ambient conditions and, fouling of the internal components. During a recent harsh summer operation, the compressor was undergone to surge many times and prompted to initiate a performance evaluation study to identify the cause(s) of surge and the extent of performance deterioration. High cooling water supply temperature and ambient conditions crippled the performance of the compressor. Engineering analysis identified the excessive accumulation of condensed water in the water chamber of the second intercooler as the most logical reason of the compressor surge during the instances of high ambient conditions i.e. relative humidity and temperature greater than 80% and 35°C, respectively. During heavy load of condensed water, the blockage and insufficient size of the condensate drain caused build up of water level in the water collecting chamber which offered instantaneous hindrance to airflow to the next section and, hence, led to the compressor surge. During normal ambient conditions, the overall performance of the compressor was found satisfactory when compared with the commissioning after a long term of continuous operation without maintenance.