Analysis of Combustion Chambers in Internal Combustion Engine

Global Science and Technology Journal Vol. 2 No.1 March 2014. Pp. 12-21 Analysis of Combustion Chambers in Internal Combustion Engine Ariz Ahmad* Abstract: The main objective of this paper is to study various types of combustion chambers in petrol engines, diesel engines, gas turbine, jet engines and steam engines and how they are different from each other in terms of their design, fluid flow characteristics and mechanisms. This paper also discusses about combustion chambers and technologies used in current generation of vehicles and concept designs for future generation of engines. This paper also includes flow simulation, surface plots and area plots modeling of combustion chambers using various parameters and report generated for the overall process of combustion on solid works. Field of Research: Internal Combustion Engines 1. Introduction A Combustion Chamber is a part in which combustion of fuel or propellant, in particular, is initiated in internal combustion engine The combustion technology increases the inner power of a gas, that translates into a rise in temp, pressure, or volume reliant on the specification in an enclosure, for instance the cylinder of a repayment engine, the volume is manipulated & the combustion creates a rise in pressure. In a constant flow arrangement, for example a jet-type engine combustor, the compression is initiated & the burning makes an rise in volume. This rise in compression or volume can be utilized to do work, for example, to push a piston on a crank or a engine disc-type in a gas turbine. For this paper references where taken from various books, online papers from different authors and handful of websites and blogs for the stimulations and CFD analysis solid works software being used and designing of combustion chambers were done on Catia. This paper was solely done by one author. In this paper significance was given towards functioning of different types of combustion chambers and how the fluid flows inside the combustion chamber at different parameters represented in CFD simulations. In Sec 2, theoretical aspects of the paper is covered. In that we discuss about definition of the combustion chamber, its functionality, its classification in various types of engines and also includes discussion about current and future technological improvements of the combustion chamber. In Sec 3, methodology involved in CFD (computerised fluid dynamics) about combustion chamber is explained. Results obtained from the analysis which is accumulated in the form of table is presented in Sec 4 and finally Sec 5 is the conclusion for this research paper. *Ariz Ahmad, Department of Mechanical Engineering, BITS - Pilani, Dubai, United Arab Emirates. Email: arizahmad@gmail.com, 12

2. Theoretical Underpinnings Combustion chamber is one of the most important component of the internal combustion engine. It is from where the combustion begins and initiates the work of the engine. There different types of combustion chambers of different shapes and sizes (Ganesan, 2008). Different types of combustion chamber used in petrol or gasoline engines are: 1. T - head type: This configuration provides 2 valves on either side of the cylinder, requiring two cram shafts. 2. L - head type: A modification of T-head type combustion chamber is the L- Head type which provides 2 valves on the same side of the cylinder and the valves are operated by a single camshaft. 3. I - head type: It is also called overhead valve combustion chamber in which both the valves are located on the cylinder head. 4. F - head type: This arrangement is a compromise between L-head and I- head types. Combustion chamber in which one valve is in the cylinder head and the other on the cylinder block are known as F-head combustion chamber (Ganesan, 2008). In diesel engine the combustion chambers are divided based on the injection type used (Ganesan, 2008).There are two types of injection used namely: 1. Direct injection: also called as open combustion chamber, in this type of combustion chamber, the entire volume of the combustion chamber is located at the main cylinder and the fuel is injected into this volume the main advantage is minimum heat loss during compression because of lower surface area to volume ratio and no cold starting problems. The main disadvantage is high fuel injection pressure and necessity of accurate metering of fuel by the injection system. 2. Indirect injection: this type of combustion chamber the combustion space is divided into 2 parts one is the main cylinder and other is the cylinder head. The main advantage is that the injection pressure required is low. Drawbacks are cold starting problems because of this we require heater plugs, specific fuel consumption is high because of loss of pressure (Ganesan, 2008). Different types of Direct Injection combustion chambers are: 1. Shallow depth chamber: The depth of the cavity in the piston is quite small. This chamber is adopted for large engines running at low speeds. 2. Hemispherical chamber: The chamber gives a small squish. The depth to diameter ratio for this chamber can be varied to given any desired a squish to give better performance. 3. Cylinder chamber: It is a form of truncated cone with a base angle of 30 degrees. The swirl was produced by making the inlet valve for nearly 180 degrees of circumference.squish can also be varied by varying the depth. 4. Toroidal chamber: It has such a shape so as to provide a powerful squish along with the air movement within the toroidal chamber. Mask needed for inlet valve is very small so as to provide the powerful squish (Ganesan, 2008). 13

Different types of Indirect Injection combustion chambers are: 1. Swirl chamber: Chamber in which swirl is generated. 2. Pre-combustion chamber: Chamber in which combustion swirl is induced. 3. Air cell chamber: Both combustion and compression are induced (Ganesan, 2008). Combustion chamber in gas turbines and jet engines are called as combusters. The compression system feeds the combuster. With highly pressurized air and puts fuel and ignites the mixture. It then feeds the hot, high pressure exhaust into the turbine parts of the engine and the remnants comes out from exhaust nozzle (Benson, 2005). The different types of combusters are listed below: 1. Can: They are self-contained cylindrical chambers, in which each can has its own fuel injectors, liners, interconnectors, casing, Each can get an air source from individual opening. The can-type combustion chamber is typical of the type used on both centrifugal and axial flow. 2. Can-annular: Unlike the can-combuster, all the combustion zones share a common air casing. Can- annular combustion chambers are arranged radially around the axis of the engine. They are enclosed in a removable steel shroud that covers the entire burner section and makes it available for servicing without problems. 3. Annular: It has separate combuster zones and simply have non-stop liner and casing in a ring is called the annulus. The annular-type combustion chamber is used in many engines designed to use axial flow systems (Benson, 2005). The current combustion technology used in this generation of internal combustion engines are listed below: 1. Hemi engine: A Hemi engine is an internal combustion engine in which the roof of each cylinder's combustion chamber is of hemispherical form. The current production Hemi engine heads are not truly hemispherical in shape. It uses a coil-on plug distributor less ignition system and 2 spark plug per cylinder to shorten flame travel leading to more consistent combustion which helps reducing emission (Marshall, 2003). 2. Direct injection turbo: To make big engine power with small engine fuel economy, many companies are turning to smaller engines with turbochargers, direct fuel injection and variable valve timing thereby forcing additional air into engine combustion chambers with a turbo charger definitely boosts power. But this technology also leads to harmful detonation (knocking). The solution to this problem was cooling the intake charge hence minimizing detonation (Car & Driver, 2010). 3. Lean burn engine: It is lean amount of fuel supplied and burned in engine combustion chamber. Normal air-fuel ratio is 15:1, true lean burn can go as high 23:1. Lean burn engines enjoy high fuel economy and cleaner emissions than conventionally tuned engine. The down fall of lean burn engines is the emissions on NOx gas due to higher heat and cylinder pressure & somewhat narrower RPM power-band due to slower burn rate of lean mixtures. Vehicles that use this technology require complex catalytic converters thereby limiting to light duty vehicles (Saxena, 2003). 14

4. Combined combustion system: Volkswagen unveiled what it claims is the internal combustion engine of the future. Called the Combined Combustion System (or CCS for short) it mixes the most favourable characteristics of both petrol and diesel technology to make one low emissions, high efficiency power unit which runs on synthetic bio-fuel. The fuel mixture that enters each of the[6] CCS' cylinders is fully vaporised and ignites over a larger area than it might in a conventional engine. in much the same way as a modern day direct injection petrol unit does. This early firing reduces the build up of nitrous oxide and particulates caused by non-vaporised fuel and hot spots within the cylinder Because the fuel mixture is ignited over a longer period, the CCS unit also proves more economical (Volkswagen, 2006). 5. Intelligent dual sequential igniton (i-dsi): The dual sequential ignition system optimizes the timing of each spark plug based on engine speed and engine load. The intensive combustion at all engine speeds not only controls knocking, but also permits a much higher compression ratio (10.8:1) to achieve a higher output with less fuel consumed compared to a conventional design. Key to the i-dsi engine is rapid, intensive combustion, using two spark plugs in each cylinder mounted diagonally opposite one another, and a very compact, high-swirl combustion chamber made possible by the narrow (30 ) valve angle and SOHC single pivot cylinder head. Each pair of spark plugs is fired sequentially with the interval between the two depending on engine rpm and load. (Honda, 2010) 6. Transonic combustion system (TSCITM): The Transonic Combustion system (TSCITM) is a new combustion process for the gasoline internal combustion engine. The TSCITM combustion process utilizes direct injection of fuel into the cylinder as a supercritical fluid based on the patented concept of injection-ignition. Supercritical fuel promotes rapid mixing with the contents of the cylinder which, after a short delay, results in spontaneous ignition at multiple locations. Multiple ignition sites and rapid combustion combine to result in optimum heat release and high cycle efficiency it is capable of operating over a wide range of air-fuel ratios and so does not require a throttle for load control. TSCiTM has inherently short combustion delay and rapid combustion that result in heat release phasing for optimal efficiency.the potential of the technology is to provide real world fuel consumption reductions of 25% to 30% in gasoline fuelled passenger cars with corresponding reductions of greenhouses gases. (Transonic Combustion, 2006) 3. Methodology The methodology applied for this research is that of CFD Analysis which is briefly explained below: a) In this analysis we will discuss the flow simulation of combustion chamber (can- annular & jet type). b) Parameters used in the analysis nare temperature and pressure. c) External flow analysis is done. d) Axis selected is X-axis. 15

e) Fluid used is air. f) Temperature inputted is 373 K. g) Computational domain is selected to simplify the computing. h) Global goals like total pressure and frictional force is defined. i) Run the simulation. j) Get flow trajectories in terms of pressure. k) Get surface plots and cut plots. Figure 1: Flow Trajectory in Combustion Chamber Indicating Pressure The above diagram indicates the pressure flow the can type combustion chamber. Air gets inside the combustion chamber through the liners and then the air circulates and the combustion takes place at a certain pressure and then leaves the combustion chamber. Different colours indicating different values of pressure in pascals (Pa). 16

Figure 2: Surface Plot of Combustion Chamber Displaying Pressure Surface plot indicates the amount of pressure on the surface of combustion chamber when the wir is flowing through it. Different colours indicate different pressure in this animation. Figure 3: Flow Trajectory in Combustion Chamber Indicating Pressure Similar to that of can-type, flow trajectory is shown in the above diagram for pressure. 17

Figure 4: Surface Plot of the Combustion Chamber Displaying Pressure Similar to can type combustion chamber the surface plot is given for jet-type combustion chamber in which different colours indicate different pressures. Figure 5: Cut Plot of Combustion Chamber Indicating Pressure Cut plot indicates the combustion chamber cutting through the surface at a certain pressure. Jet type combustion chamber is used for this kind of simulation. 4. Results There were two experiments performed using the above methodology with different number of iterations. The results of these experiments are represented in the form of two tables shown below: 18

Table 1: Report Generation for Can-Annular Combustion Chamber Goal Name Unit Value Averaged Value GG Max Total Pressure 1 [Pa] 1.015037k 1.01503436k GG Max Velocity 1 [m/s] 14.14 14.13 GG Max Velocity (X) 1 [m/s] 2.88 2.87 GG Max Turbulent Viscosity 1 [Pa*s] 0.016 0.016 GG Friction Force 1 [N] 0.03 0.03 GG Friction Force (X) 1 [N] -0.03-0.03 Report generated for can-annular combustion chamber Iterations: 159 Analysis Interval: 47 Table 2: Report Generation for Jet Combustion Chamber Goal Name Unit Value Averaged Value GG Max Total Pressure 1 [Pa] 1.01646k 1.01649k GG Max Velocity 1 [m/s] 24.95 24.936 GG Max Velocity (X) 1 [m/s] 6.34 6.38 GG Max Turbulent Viscosity 1 [Pa*s] 0.01754 0.01752 GG Friction Force 1 [N] 0.0129 0.0128 GG Friction Force (X) 1 [N] -0.0129-0.0128 Report generated for jet combustion chamber Iterations: 137 Analysis interval: 36 5. Conclusion Combustion chambers play a vital role in internal combustion engine. The amount of heat that is produced depends upon the shape and size of combustion chamber. For improving engine efficiency and performance the combustion chambers of different shapes and sizes are being developed by Vehicle manufacturers to have a lead in the competition. New innovations in engine combustions technology (like tdi, blue tec, etc ) have been developed to tackle the challenges set by government and societies. 1. To produce a high performance at cheaper price so as to compete with other vehicle manufacturer. 2. Efficiently consuming fuel so as to tackle the scare of replenishing crude oil and rising fuel prices. 19

3. Develop engines with alternate fuels without hampering the performance. 4. Low emissions to be environment friendly. There are however few limitations which are listed below: 1. There can be a potential heat loss and pressure loss when fluid flows through large cross- section area of combustion chamber. 2. Sometimes during cold weather an external device like glowplugs are required for ignition. 3. Maintenance can be hazardous due to presence of residual fuel or gas during shut down. 4. Sometimes due to high pressures there can be potential cracks developments in the chamber which can interrupt the fluid flow thus, can have a significant consequence in the whole process. Research is still carried on new designs of combustion chamber as well new combustion technology so as to support the future generations of vehicles and also meet future demands. New innovations in engine combustions technology (like tdi, blue-tec, etc ) have been developed to tackle the challenges set by government and societies. Listed below are the challenges faced by the companies dealing with internal combustion engines: 1. To achieve high performance at cheaper price so as to compete with other vehicle manufacturer. 2. Efficiently consuming fuel so as to tackle the scarce of replenishing crude oil and rising fuel prices. 3. Develop engines with alternate fuels without hampering the performance. 4. Low emissions to be environment friendly. CFD flow simulation on pressure as well as surface plot and cut plot animations were done on can type and jet type combustion chambers. CFD flow simulations can further be done other parameters like viscosity, force etc. which will be represented in future research. References Benson, T. (2005), Jet Engine, The Jet Engine Components, Vol.1, Pp.1, retrieved 5 th march 2013, http://www.pilotfriend.com/training/flight_training/tech/jet_engine_component s.htm Car and Driver (2010), Direct Injection Turbo, The Future of the Internal-Combustion Engine, Vol. 4, Pp.11-13. Ganesan, V. (2008), Combustion in Combustion Chambers, Internal Combustion Engines, 3 rd ed, Khanna Publishers, India, Pp. 369-407. Honda (2010), Intelligent dual Sequential Ignition, Intelligent-Dual Sequential Ignition (idsi), Vol.1, Pp.1, retrieved 10 Feb 2013, <http://www.honda.co.nz/technology/engine/idsi/> 20

Marshall, B. (2003), Hemi Engine, How Hemi Engine Works, retrieved 16 February 2013, <http://science.howstuffworks.com/transport/enginesequipment/hemi.htm> Saxena, A. (2003), Lean Burn Engines, Optimum Fuel Systems, vol.1, Pp. 1-3, retrieved 30 December 2012, <http://www.optimumfuelsystems.com/index_htm_files/dynoreports.pd Transonic combustion (2006), transonic combustion, About Transonic combustion system (TSCITM), retrieved 10 Feb 2013, Vol.1, Pp.1, <http://www.tscombustion.com/?page_id=845> Volkswagen (2006), combined combustion system, Combined Combustion System (CCS) Technology, Vol.1, Pp.1, retrieved 7 th Feb 2013, <http://www.germancarforum.com/community/threads/combinedcombustion-system-ccs-technology-autocar-autobild-reviews.8981/> 21