The Split-Cycle Engine Essay Example for Free

The Split-Cycle Engine Essay The Split-Cycle Engine changes the heart of the conventional engine by dividing (or splitting) the four strokes of the Otto cycle over a paired combination of one compression cylinder and one power cylinder. Gas is compressed in the compression cylinder and transferred to the power cylinder through a gas passage. The gas passage includes a set of uniquely timed valves, which maintain a prechargedpressure through all four strokes of the cycle. Shortly after the piston in the power cylinder reaches its top dead center position, the gas is quickly transferred to the power cylinder and fired (or combusted) to produce the power stroke. Split-cycle internal combustion engine claims have the potential to double fuel efficiency for same size engine, while reducing the manufacturing price by up to 50% which includes a built in dedicated compressor. Rather than using batteries and electric motors/generators to harness braking energy, the engine uses the air compressor. A split cycle engine includes a novel compressor apparatus driven by the combustion engine, a closed-cycle refrigeration system in cooperation with the compressor apparatus, and a pneumatic motor driven by compressed air from the compressor apparatus. Refrigerant in the compressor absorbs thermal energy from compressed air and assists in compressing the air. High-pressure air from the compressor is stored in a storage tank and may be used to drive the pneumatic motor or other auxiliary equipment in addition to providing high-pressure combustion air for the internal combustion engine Introduction An engine includes a crankshaft having a crank throw, the crankshaft rotating about crankshaft axis. A compression piston is slid ably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke of a four stroke cycle during a single rotation of the crankshaft. An expansion piston is slid ably received within an expansion cylinder. A connecting rod is pivotally connected to the expansion piston. A mechanical linkage rotationally connects the crank throw to the connecting rod about a connecting rod/crank throw axis such that the expansion piston reciprocates through an expansion stroke and an exhaust stroke of the four stroke cycle during the same rotation of the crankshaft. A non-circular path is established by the mechanical linkage which the connecting rod/crank throw axis travels around the crankshaft axis. Moving Engine Technology into the 21st Century The first four-stroke piston engine was developed in 1876. This four-stroke piston arrangement is still the primary design of engines built today. Today’s engines operate at only 33% efficiency. This means that only 1/3 of the energy in each gallon of fuel is used the rest is lost through friction and heat. With over a billion engines currently in use worldwide, even small gains in efficiency will have huge impacts on the economy, dependency on foreign oil, and the environment. Despite immense efforts over the past century, engine efficiency has remained the same. The Heart Of The Engine Needs To Change: The heart of the internal combustion engine is a piston moving up and down in a cylinder connected to a crankshaft. Its simplicity makes improving performance almost impossible. Small improvements have proven difficult and large improvements have been considered impossible. Improving the four-stroke piston design has become the Rubik’s Cube of engineering, a puzzle that nobody has been able to solve until now. While the industry struggles for gains in the 1% range, the design of the Split-Cycle Technology pushes engine efficiency and performance to an entirely new level. Conventional Engine Design The heart of the internal combustion engine is a piston connected to a crankshaft, moving up and down in a cylinder through the four strokes of the Otto Cycle, the intake, compression, power and exhaust strokes. In a typical four-stroke cycle engine, power is recovered from the combustion process in these four separate piston strokes within each single cylinder. This basic design has not changed for more than 100 years. The Various Strokes And Stages Involved A. Intake and Compression: The basic concept of the Split Cycle Engine is to divide the four strokes of a standard engine over a paired combination of one compression cylinder and one power (or expansion) cylinder. These two cylinders perform their respective functions once per crankshaft revolution. The concept is illustrated in Figures 1 through 8. A common misconception is that twice as many cylinders are required. This is simply not accurate. Because this engine fires every revolution instead of every other revolution, the number of power strokes produced is equal to the power strokes produced by two of the conventional piston/cylinder designs. A four cylinder engine would still have four cylinders. There would simply be two sets of paired cylinders instead of four individual cylinders. In the configuration shown, an intake charge is drawn into the compression cylinder through typical poppet-style valves. B .Compression Stroke The compression cylinder then pressurizes (Fig. 2) the charge and drives the charge through the crossover passage, which acts as the intake port for the power cylinder. In this illustration, a check valve (best seen in Figures 6, 7 and 8) is used to prevent reverse flow from the crossover passage to the compression cylinder, and likewise a poppet-style valve (crossover valve) prevents reverse flow from the power cylinder to the crossover passage. The check valve and crossover valve are timed to maintain pressure in the crossover passage at or above firing conditions during an entire four stroke cycle. C. Power and Exhaust: Combustion occurs soon after the intake charge enters the power cylinder from the crossover passage. This means that the start of combustion occurs after the power cylinder passes through its top dead center position. The resulting combustion drives the power cylinder down. Exhaust gases are than pumped out of the power cylinder through a poppet valve to start the cycle over again. D. Previous Split-Cycle Designs There have been other similar split-cycle engine designs in the past, but they have never been able to match the thermal efficiency levels of the standard four-stroke engine. This is due in large part to the fact that, as the gas is transferred from the crossover passage to the power cylinder in the prior engine designs, the gas has always been allowed to over-expand in the power cylinder and then must be recompressed before initiating combustion. The extra work required to recompress the gas greatly reduces efficiency levels.