Project Title

Improving the Performance Characteristics of a Large Split Cycle Engine using CFD Approach

Proposed Research

The Proposed Research is Basic

Research Domain

Research mainly focuses Science, Engineering & Technology

Field of Research

Major: Mechanical Engineering

Specialization: IC Engine

Project Digest

The prime Focus of this project is to improve efficiency of the split cycle engine by increasing the overall thermal efficiency of the engine. This is done primarily by changing the design approach of the crossover passage. A crossover passage connects between the compression and expansion cylinders and includes compression (XovrC) valve and a crossover expansion (XovrE) valve. It consists of a fuel injector. The crossover passage transfers the compressed air from the compression cylinder to the expansion cylinder and maintains the pressure in between the two cylinders. Unlike conventional engine which are fired before top dead center split cycle engine are fired after top dead center. Crossover passage is designed helical which creates maximum turbulence. The turbulence is further enhanced by keeping the valves open as long as possible during combustion. The combination of high starting pressure and fast flame speeds enables combustion to start between 11 & 15 after top dead center and ends 23 degrees after the ignition. As maximum turbulence is needed to

Bulk swirl creation of Air Fuel mixture Swirl is creation of the large movement of air that are large rotating vortex. Air contains

more K.E Frequency of turbulence and micro turbulence eddies( air circular motion) 10 to 10000

Hz Engine combustion is depend upon to phenomena Swirl or Turbulence.

The result is a split cycle engine with better efficiency and great performance than a conventional Engine.

Name of Investigator

Muhammad Zeeshan Rafique

Highest Degree

M.Sc. Automobile Engineering Management

Position

Assistant Professor

Department

Department of Mechanical Engineering

Duration

Estimated project duration is 3 years in which the project is further divided into 3 Sub-Categories

Project Summary

Split-cycle engines has two separate but paired cylinders. It has a crankshaft that is rotatable about an axis. A compression piston that reciprocates through an intake and compression stroke within the compression cylinder and expansion piston reciprocates through expansion and exhaust stroke within the expansion cylinder, both pistons are connected to a single crankshaft. The cycle is completed in single rotational of crankshaft.

Helical crossover passage is connecting the compression and expansion cylinders. Helical crossover passage which includes crossover compression valve and crossover expansion valve thus defining a pressure chamber there between, generally straight runner section in a downstream portion of the helical crossover passage, and a helical end section integrally connected to the runner section and disposed over the crossover expansion valve, the crossover expansion valve which includes a valve stem and head, the helical end section enclosing a funnel spiraling about a valve stem, where in the funnel forces the incoming air to rotate about valve stem prior to entering the expansion cylinder to promote development of turbulent kinetic energy and swirl in the air/fuel charge development to the expansion cylinder. Tangential runner section which directs air flow into the funnel of the helical end section.

Hypothesis

Goal is to increase thermal efficiency of split cycle engine, considering the design improvement of crossover passage in split cycle engine. Overall Thermal efficiency can be increased via crossover passage. The crossover passage is a major control point for the engine. It is utilized for controlling pre-detonation by providing an additional cooling point after compression has occurred. This is a feature unique to the split-cycle design that is simply not possible in a conventional engine.

Helical shape of crossover passage is selected because it increases heat transfer rate and creates centripetal effect. Due to this effect all the fuel particles are attracted toward center and good air fuel mixture is formed. The main purpose of helical crossover passage is to create Maximum turbulence and swirls. The runner shape of crossover passage is also affected by the amount of drag. The round surface have less drag and minimum loss of heat than flat once. Narrow surfaces have less drag than the wide once. More air hits the surface and hence more drag produces. Edges must be round for the crossover passage.

Goal

Research’s main goal is to maximize the thermal efficiency by using helical crossover passage, and by introducing a Nozzle in between the Helical Passage.

Results can be verified by mathematical modelling of the cross over passage using CFD analysis thus designing a crossover passage having the same pressure at both end of the port.

Introducing the helical arrangement in the crossover passage thus improving the turbulence and maximum swirl creation

Finally introduction of a nozzle in the helical crossover passage for injecting air with maximum velocity

Objectives

Primary Objectives includes:

Dual helical crossover passage is used in our project to increase the velocity which increases the evaporation, mixing, mass transfer and thermodynamic transfer rates within a combustion cylinder.

The fuel injector is used in the runner. When air-fuel mixture will pass through helical shape it will form the bulk swirl and good air-fuel mixture. These bulk swirl will enter in the combustion cylinder as vortex.

The helical crossover passage creates high turbulence near the TDC when ignition occurs. It break up and spreads the flame front many times faster than that of laminar flame. The air-fuel is consumed in a very short time, self-ignition and knock are avoided.

Due to firing ATDC the overall efficiency of the engine increases because less forces acting on the connecting rod .This allows the crank to rotate with much less resistance giving the engine more power and speed.

The runner shape of crossover passage also affected by the amount of drag. The round surface have less drag and minimum loss of heat than flat once. So the edges of runner should be round.

Introduction

Split-cycle engines separate the four strokes of Intake Compression Power and Exhaust Into two separate but paired cylinders. The first cylinder is used for intake and compression. The compressed air is then transferred through a crossover passage from the compression cylinder into the second cylinder, where combustion and exhaust occur.

The crossover passage is a major control point for the engine. It is utilized for controlling pre-detonation by providing an additional cooling point after compression has occurred. This is a feature unique to the split-cycle design that is simply not possible in a conventional engine.

Helical crossover passage valve including a valve stem and head. The helical end section enclosing a funnel spiraling about the valve stem. The flow area within the helical end section is disposed (Slop) is circumferential and descending funnel around the valve stem. Where funnel force incoming air rotate about valve stem prior entering the expansion cylinder to promote turbulence K.E in cylinder.

Helical crossover passage is too good because it increase heat transfer rate and creates centripetal effect. Due to this effect all the fuel particles are attracted toward center and good air fuel mixture is formed. The main purpose of helical crossover passage is to create turbulence and swirls.

Background of Research Problems to be addressed

Split-cycle engines appeared as early as 1914. Many different split-cycle configurations have since been developed; however, none has matched the efficiency or performance of conventional engines. Previous split-cycle engines have had two major problems

Poor Breathing (Volumetric Efficiency) Low Thermal Efficiency

Poor Breathing (Volumetric Efficiency)

The breathing problem was caused by high-pressure gas trapped in the compression cylinder. This trapped high pressure gas needed to re-expand before another charge of air could be drawn into the compression cylinder, effectively reducing the engine’s capacity to pump air and resulting in poor volumetric efficiency.

Low Thermal Efficiency

The thermal efficiency of split-cycle engines has always been significantly worse than a conventional Otto cycle engine. The primary reason: They all tried to fire like a conventional engine — before top dead center (BTDC).

In order to fire BTDC in a split-cycle engine, the compressed air, trapped in the crossover passage, is allowed to expand into the power cylinder as the power piston is in its upward stroke.

By releasing the pressure of the compressed air, the work done on the air in the compression cylinder is lost. The power piston then recompresses the air in order to fire BTDC.

By allowing the compressed gas in the transfer passage to expand into the power cylinder, the engine needs to perform the work of compression twice. In a conventional engine, the work of compression is done only once; consequently, it achieves much better thermal efficiency.

The new Split Cycle Engine solves both the problems:

Unique Valve Design (Resolving the Poor Breathing Problem thus improving volumetric Efficiency)

Firing after top dead center (Resolving the Thermal Efficiency Problem)

UNIQUE VALVE DESIGN

On the compression side of the Scuderi Engine, the breathing problem is solved by reducing the clearance between the piston and the cylinder head to less than 1 mm. This design requires the use of outwardly opening valves that enable the piston to move very close to the cylinder head without the interference of the valves.

This effectively pushes almost 100 percent of the compressed air from the compression cylinder into the crossover passage, eliminating the breathing problems associated with previous split-cycle engines.

FIRING AFTER TDC

Although considered bad practice in conventional engine design, firing ATDC in a split-cycle arrangement eliminates the losses created by recompressing the gas. The big issue was not how to solve the thermal efficiency problem of the split-cycle engine, but rather how to fire ATDC.

In fact, determining how to fire ATDC is possibly the single most important breakthrough of the Scuderi Engine design. The combination of high starting pressure and fast flame speed enables combustion to start between 11 and 15 degrees ATDC and end 23 degrees after ignition. The result is a split-cycle engine with better efficiency and greater performance than a conventional engine.

References

1. Ganesan V (2007), Internal Combustion Engines, Tata McGraw Hill Education Pvt Ltd.

2. Patent No. US 2005/0268609 A1, Date December 8, 20053. http://en.wikipedia.org/wiki/Split_cycle_engine 4. http://en.wikipedia.org/wiki/Scuderi_engine 5. http://www.scuderigroup.com/engine-development/ 6. http://www.scuderigroup.com/ 7. http://www.popsci.com/cars/article/2011-01/split-cycle-engine-design-could-

improve-fuel-economies-50-percent8. http://phys.org/news/2011-01-split-cycle-efficient-traditional-combustion.html 9. http://www.engineeringtv.com/video/Split-Cycle-Four-Stroke-Engine 10. http://www.greencarcongress.com/2013/06/scuderi-20130601.html 11. http://gas2.org/2013/09/26/scuderi-split-cycle-engine-being-used-as-lpg-air-hybrid-

generators/12. http://www.prnewswire.com/news-releases/scuderi-group-signs-agreement-with-

worldwide-engine-manufacturer-210382971.html

Principal Investigator (Resume)