COMMENTS AND DISCUSSIONS

combustor. Relative to these conditions, we are studying, in association with university faculty, the design of such a combustor operating at said stoichiometric conditions.

Author’s Reply to Comments of Mr. Carl 0. Brady

Mr. Brady has been quite generous with h,is insightful re- marks. He too touches on the critical elements of reliability, availability, and maintainability, and he recommends much- needed analysis on installation cost, ease of automation, and support-system impact. Again, we concur that many issues he has raised must be addressed in future endeavors.

Mr. Brady confronts the cost issue. He notes that we have

Paper #3: [52]

Comments

assigned a value of 25,000 hp to the nominal power rating of the LM2500, whereas a realistic updated power rating is 29,500 hp. Therefore, the baseline engine, which should vi- tiate the validity of any argued advantage based on competi- tive costs.

However, our argument is based upon the air consump- tion of the alternative engines. One engine requires only one-third the air consumption of the other. For any chosen power rating, whether it be 25,000, 26,000, or 29,500 hp, this air consumption is a crucial factor determining the cost of the engine in question. Based upon this fact, we believe our cost assessment is valid.

MAIN PROPULSION POWER TAKE-OFF CONFIGURATION FOR A

ETC GUN PULSED POWER GENERATOR

KENNETH E. PETTERSEN CHARLES L. BIELITZ

JOHN CIANCI

by

By: Zvi Karni, JJMA

I would like to thank the authors of this interesting paper for sharing with us some of the considerations involved in selecting a major machinery component. When reviewing a single report which highlights only a few aspects of a com- plex picture there is often difficulty. I hope the authors will augment the unclear or missing information in their re- sponse to this review.

Six major issues are suggested in the abstract: space con- straints within the main engine and auxiliary rooms, gear sizing, survivability, shock and vibration, bulkhead penetra- tion and equipment accessibility. The authors concentrated on the first two issues, configuration and gear sizing, and only briefly addressed the remaining considerations.

Although the introduction section is almost entirely devot- ed to the ETC gun concept, the significance of this concept in terms of actual power. loading, load sharing with the propul- sion system, and load variation is not emphasized. Since the “real” average and peak power requirements and the number of load cycles greatly affect the size of the PTO gear (and the size and weight of the generator), the sensitivity to the as- sumptions used in the study should be investigated. For ex- ample, assuming a life expectancy for the PTO gear based on 30 shots-per-hour for 17 consecutive years may be unrealistic. The optimization process should include operational con- straints as well as material and configuration physical limits.

These issues lead to a more general subject. The authors do not establish quantitative objectives and most of the con- straints presented in the paper are qualitative. Thus the con- clusions of the paper are soft.

The objective may be the least weight of the system, or

the least cost. It may also be multi-objective with weights attached to each independent objective. The constraints should either pasdfail, or be weighted and combined into a rationale set of constraints. In short, a system approach where, for example, the modification of the machinery room bulkhead to accommodate the “optimal” configuration in terms of size, weight, cost and survivability may be,recom- mended in-spite of naval architectural traditions.

Five optional arrangements were identified for downse- lection. Four of these are depicted in figures while two vari- ations of the fourth option, the right angle bevel gear and the fifth options are discussed. A sixth configuration, potentially the optimal one, is mentioned very briefly. Can the authors add sketches to clarify their comments? Can the PTO gear be de-clutched from the gas turbine when its service is not required?

Points requiring further clarification: Differentiating between the MRG and the PTO gear in the

Gear Rating and Sizing sections is difficult. When stating “Gear rating is 26,580 hp at 3,600/8,000 rpm” - which gear is it? (The LM2500 200 Megawatts of power = 25,775 hp). Later, while discussing Option 5 it is unclear from the test whether the LS gear is the bull gear? If it is the bull gear why is it limited to a tangential driving force of 105,838 lbs. and why isn’t it sufficient to generate a power of 15,804 hp or 11,800 KW which is more then required for a single gen- erator (Why 22,156 hp is required at the generator?)

The statement “Rotor sizes for options 1 and 3 were de- termined by proportioning” in the Gear Data section is not clear. Can the authors clarify the paragraph?

The major issues referred to in the abstract such as shock, vibration and survivability, are mentioned briefly in the con- clusion section. Have these issues been made public?

In conclusion, the paper presents an interesting feasibility

Naval Engineers Journal, July 1994 103

COMMENTS AND DISCUSSIONS

study and a rationale downselection process. And as the au- thors state, once the design process of the system starts to converge, the optimal configuration may be identified easier and as they pointed option 6 looks promising.

Author’s Reply

The authors appreciate Mr. Karni taking the time to re- view this paper. Several of his comments may be addressed together by restating and clarifying the purpose of this in- vestigation. This Power Take-Off (PTO) gear is a small part of a large system. This study was undertaken early in the system design process to identify the best candidate gear de- signs, while recognizing that the final choice will be made later in the process based on new information and further analysis. Even at that time, however, there will be no “quan- titative objective” for the gear design itself but what is known about the various gear design operations will be studied for its impact on the quantitative objectives for the system.

In the gear rating section, it should be understood that this system runs under dynamic loading conditions so variable as to make the nominal desknation of the generator as a 10 MW machine almost meaningless for operational purposes. The PTO gear is rated at a much higher torque level to ac- count for the dynamic loading as described in Reference 2. In the case of the RACER pinion that Mr. Karni questions, the single pinion in mesh with the bull gear is limited to the Main Reduction Gear specification level of 350-K-factor and, although it could handle the nominal 10 MW generator load, it is not sufficient to handle the dynamic generator load.

We trust that today’s presentation, which includes figures not available to Mr. Karni when he reviewed the paper, has sufficiently clarified what each of the arrangements entails. Much of the requested additional detail, which we agree needs to be developed, will be covered in a further study of the Through Bulkhead Arrangement and the Side Mount Configuration. The Casing Extension Configuration will also be studied in depth, if the generator size is sufficiently reduced.

Paper #4: [59] FUEL CELL POWER PLANTS FOR SURFACE FLEET APPLICATIONS

PHILIPPE GOUBAULT, MARC GREENBERG, TODD HEIDENREICH & JOE WOERNER bY

By: R. Michael Adair P.E. Principal Electrical Engineer Bath Iron Works Corp.

In this paper, the authors look at today’s world and tech- nology and try to extrapolate that data into the future by 30 or 40 years. They are not only trying to evaluate technology that doesn’t exist today, they are comparing it to gas tur- bines and diesels that most certainly will also change over that period. Recognizing that the prediction of the future is always risky business, the authors have shown that the fuel cell is practical technology that offers significant advantages if it can be made to fit an application. Although much devel- opment is required before one will power a destroyer, the technology is currently undergoing rapid development.

In reviewing the paper it appears there are three signifi- cant topics. The first, already discussed, is that fuel cell technology is practical and, with development, is potentially practical for ship applications. In the second area, the paper evaluates a method to determine the requirements for a fuel cell plant. The authors appear to have gone into consider- able detail in the development of their estimates and posi- tions. Given the uncertainty of the parameters, a discussion of the specific numbers may not be worthwhile. Taken as a whole, the authors clearly justify their argument that fuel cells can replace diesels and gas turbines in the future.

It is noted that the paper uses distributed generator sys- tems as a point of comparison. That concept has not been accepted for use and, therefore, may not be a good basis for comparison. Also, the evaluation of a destroyer with two en-

gines does not consider the possibility of a total of four propulsion gas turbines, as in the current DDGJ 1 design. A design that retains any gas turbines would retain problems such as those associated with intakes and exhausts.

The authors have examined how fuel cells might perform in shipboard application. They show their parameters and evaluation methods in a comparison with existing ship de- signs. The type of information developed is needed to guide and evaluate the development of fuel cell technology and systems. The authors also have described the benefits in- cluding improved efficiency, a lower environmental profile, improved military features, and improved flexibility in the development of ship arrangements. An understanding of the benefits is needed to justify the development costs.

The third point made is that the required technology is not complete at this time. In a general nature, the paper de- scribes the developments needed to make fuel cells a practi- cal alternative and describes how a development program based on commercial applications could lead to a fuel cell powered ship in about thirty years. In addition to the fuel cells, there are other technologies that, as developed, will support and improve the total ship package. As an example, the Navy is seriously working to develop direct current power distribution and propulsion systems. These changes will support the application of fuel cells that produce direct current.

As a comment, fuel cells will be used for this application when the benefits outweigh the development costs. As stat- ed in the paper, one way to mitigate the costs is to ride on the coat tails of commercial development. High-efficiency

104 Naval Engineers Journal, July 1994