Combustion Engine Generator Sets

Eric Wong, Herb Whitall, and Paul Dailey


2.1 Internal Combustion Engine Design Overview

2.1.1 Two-Stroke versus Four-Stroke

2.1.2 Engine Speed

2.1.3 Cooling Systems

2.1.4 Efficiency and Fuels

2.1.5 Emissions

2.2 Past and Current Trends in Engine Development

2.2.1 New Developements in Gas Engine Gensets

2.2.2 Increasing Speed

2.2.3 Increasing BMEP

2.3 Utilizing Existing Standby Power Gensets for DG

2.3.1 Engine Control

2.3.2 Systems Considerations for DG Applications for Combustion Engines

2.3.3 Combined Heat and Power

2.4 The Utility Interconnection

2.4.1 Open-Transition Transfer Switch

2.4.2 Closed-Transition Transfer Switch

2.4.3 Soft Loading Transfer System

2.4.4 Parallel Operation

2.4.5 Maintenance and Service

2.5 Stirling External Combustion Engines

2.5.1 Design

2.5.2 Fuels

2.5.3 Technical Developments and Outstanding Barriers

2.5.4 Controls and Communications — Dispatchability

2.5.5 Utility Interfacing

2.5.6 Costs Additional Reading

Among distributed power generation technologies, combustion engines (CEs) are the most mature prime movers. Advantages include comparatively low installed cost, high shaft efficiency, suitability for intermittent (start-stop) operation, high part-load efficiency, and high-temperature exhaust stream for combined heat and power (CHP). Additionally, a sales and technical support structure is already in place, parts are readily available and generally inexpensive, and service technicians (from both the dealer and customer's staff) have experience with maintenance and repair. Figure 2.1 shows a typical CE-based generator set (genset). This chapter details not only traditional internal combustion engine generators, but also developments in external combustion, or Stirling, engines.


Engine-generator set package (courtesy of Caterpillar, Inc., with permission).

Almost 2600 cogeneration, independent power and small power facilities, most fueled by natural gas, already existed in the United States as of the year 2000. Engine-driven generators account for 46% of the installations but only about 1.5% of the total capacity of 99 GW. Engine generator systems dominate below 1 MW capacity. Stationary reciprocating engines represent 146 GW (5%) of the world's 3000 GW of installed electric generating capacity. In the U.S., engines comprise 52 GW (7%) of 780 GW total installed capacity. In some parts of the world, engines provide a far greater share of generating capacity. For example, in The Netherlands, China, and Indonesia, engines make up more than one-fourth of total installed capacity. In the U.S., there are approximately 300,000 stationary engines. In electric power generation service, there are 76,500 diesel- and gaseous-fueled units greater than 350 kW and 150,000 units below 350 kW.

To date, the largest users of engine-driven generators are gas, electric, and water utilities. About 3100 engine generators are in use or on active standby in the electric utility industry, most at municipal utilities and rural electric cooperatives. The next largest users are manufacturing facilities, hospitals, educational facilities, and office buildings. Sales of prime movers above 1 MW — both engines and turbines — have grown significantly in the past decade. In capacity terms, reciprocating engine sales grew nearly sixfold from 1988 (2 GW) to 1998 (11.5 GW), while combustion turbine sales increased more than threefold. From 1990 to 1998, gas engine sales went from a small fraction of gas turbine sales to outselling gas turbines more than five to one in 1998. Figure 2.2 shows the trend.

Diesel engines are the leading power sources in the 1 to 5 MW size range, mainly because of their low first-cost position. However, gas engines grew

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J 300

1990 1994 199«


Gas engine and gas turbine sales trends. (Data adapted from Wadman, B., Power generation orders continue at high levels, Diesel and Gas Turbine World Wide, 29(8), 39, October, 1997.)

from 4% of engine sales in 1990 to more than 14% (of a much larger market) in 1998. That trend is likely to continue for two reasons. First, increasingly strict air emissions regulations make diesel engines impractical for continuous duty in many areas. For example, California's South Coast Air Quality Management District, which includes Los Angeles, limits stationary diesels to 200 operating hours per year. Other California air management districts and the entire state of New Jersey impose similar restrictions. Second, gas engine performance has steadily improved for the past 15 years. For example, one manufacturer reports that its gas engine fleet mechanical efficiency (400 kW and larger) increased from 31.9% in 1986 to 34.7% in 1995 — a 10% improvement in ten years. Over the same period, nitrogen oxide (NOx) emissions decreased 70%, from 14.1 to 4.0 g/bhp-hr. Diesel engines will remain viable for standby service, some peak shaving systems, and other intermittent duty. However, natural gas is already the fuel of choice for engine-driven generation involving long or frequent runs.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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