Selection of optimum equipment for gas compression applications requires a thorough comparison of both engines and compressors. Important factors to consider include first cost, operating and maintenance costs, expected service life of the equipment, compression efficiency, and regulatory compliance issues.
Engineers designed the AJAX integrals with a focus on strength and simplicity. These qualities resulted in lower operating and maintenance costs and lower downtime than is characteristic of high-speed separable packages. AJAX integrals are especially well suited for operation in remote sites with harsh conditions, such as the DPC-2803LE installations shown in Figures 1 and 2.
Selection of a gas compression package is based on many factors, one of which is the brake horsepower (BHP) of the engine. However, the main factor to consider should really be the gas compression throughput of the package. AJAX engine-compressor packages offer lower BHP/MMSCFD than high-speed separable packages, meaning that for the same rated engine power, more gas is compressed by an AJAX package than a comparable high-speed package, resulting in higher revenue over time.
AJAX packages feature an integral engine and compressor with an overall mechanical efficiency of 95%. However, separable packages consist of an engine and a compressor with two frames, two crankshafts, and their associated bearings. Considering a 95% mechanical efficiency for the engine and for the compressor, the horsepower available for compression for a separable package = 0.95 x 0.95 x engine BHP = 0.902 x engine BHP.
The single frame and crankshaft design for AJAX integral engine-compressors results in substantially fewer wearing parts than a high-speed separable package. The AJAX two-stroke engine design is illustrated in Figure 3. Unlike high-speed engines, the AJAX engine does not have intake and exhaust valves and therefore does not need a valve train, which eliminates maintenance issues with the valves and valve train. Instead, the intake air and exhaust are controlled with ports in the cylinder.
The two-stroke piston scavenged design eliminates the need for several parts, including turbocharger and aftercooler, intake and exhaust valves, rocker arms and pushrods, valve seats, camshaft and cam bearings for the intake and exhaust valves, and timing chain/gears.
The engine cycle begins with the intake air flowing through a check valve into the scavenging box of the AJAX engine. As the piston moves toward the head end of the cylinder, the intake air is pulled into the volume at the crank end of the piston. After the piston compresses the air and fuel mixture in the power cylinder, combustion occurs, which pushes the piston back toward the crank end of the cylinder. As the piston moves toward the crank end of the cylinder, it compresses the fresh air in the scavenging box. By the time that the piston timing edge uncovers the intake ports, the fresh air charge has been pressurized to about 10 psig (0.68 bar). This pressurized air then flows through the ten intake ports into the power cylinder. This process provides a boost pressure to the power cylinder without the need for the turbocharger and aftercooler which are used with the high-speed engines.
The method for controlling the air fuel ratio throughout the operating range of an AJAX engine is described in Figure 4. …
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