INTERNAL COMBUSTION ENGINE

MAB 4213

Ir. Dr. Masri Bin Baharom

LO : To understand the significance of IC Engine for Mankind

INTRODUCTION TO INTERNAL COMBUSTION ENGINES (ICE)

Definition of Combustion Engines:

-Combustion engines are machines that deliver mechanical work through a linked thermal and combustion processes.

-In this process, mechanical work is gained from the chemically bound energy of the fuel (the fuel energy) through combustion by means of thermal energy.

-The work output is gained from the gas pressure.

Examples of Internal Combustion Engine: i. Reciprocating Engine

ii. Wankel Engine (Rotary Engine)

Basic Principle of Wankel Engine:

1. Intake 2. Compression

3. Combustion 4. Exhaust

•This course only covers i. The component designs, Dynamics and forces analysis, cooling systems, etc. of Reciprocating Engines ii. The combustion processes which applies to all cases of internal combustion engines

Significance of ICE for the Industry

a) CharacteristicsCombustion engines are used widely due to a number of characteristic advantages:

- can be operated with liquid fuel of high energy density; creating a natural advantage for mobile applications- high level of efficiency (up to approximately 50% of the fuel energy can be transferred directly into mechanical work)- wide range of capacity (from approximately 30 W to 66 MW per unit)- flexible design possible (from simple robust machine to compact maximum power unit)

b) Fields of Application- Motor vehicles (in particular gasoline and diesel engines). The passenger car industry has evolved into a key market.- airplanes- construction engines (e.g., earthmovers)- agriculture (tractors, combined harvesters etc.)- railway mostly diesel engines- power plant- ships

c) Problems- Environmental concerns : Exhaust gas- Noise- Fuel supply problem

d) OutlookPossible competitors for combustion engines in the future:- gas turbine engines- electric motor + battery- electric motor + fuel cell

The combustion engine in its many configurations will certainly maintain its significance in the near future.

The latest evolution:

Classification of Combustion Engines

- closed cycle the working fluid does not change and passes through a "closed process" the combustion take place outside of the working chamber (so-called "external combustion") examples: steam engine and Stirling engine- open cycle the working fluid is the combusted fuel-air mixture; it has to be replaced after the work output (therefore "open cycle") combustion chamber = working chamber (so-called "internal combustion") examples: conventional reciprocating engine and rotary piston engine

a) Type of Cycle

b) Time Curve of the Combustion- Continuous combustion * usually for combustion engines with external combustion (Stirling engine, steam engine). * problems during internal combustion due to high thermal stress of the components * advantageous regarding exhaust and noise emissions

- Intermittent combustion * typical for open reciprocating engine processes * due to temperatures of the working fluid that are present for a short time only, the thermal stress of the components can be limited * ignition, combustion and emission problems

c) Gas Exchange

- Four-stroke cycle * volume change of the working chamber is used alternately for work output and gas exchange * control of the reciproca,ting engine through intake and exhaust valves A complete work cycle includes four cycles: 1. intake 2. compression gas-exchange cycles 3. expansion (Combustion) 4. exhaust

- Two-stroke cycle * gas exchange occurs between the working cycles by scavenging the exhaust gasses with a fresh cylinder charge * control mostly via intake and exhaust ports * in contrast to the four-stroke cycle, no valve train is necessary, but a delivery unit for scavenging air (scavenging blower) is needed * a combustion cycle includes two cycles: 1. compression 2. expansion

d) Pressure Level of the Charge

- Naturally aspirated engine * aspiration directly from the atmosphere * no additional devices needed in front of the engine to increase the charge density- Supercharged engine * increase of the charge density in front of the engine using a compressor to increase the engine power

e) Time of Mixture Generation

- Air compression (characteristic for diesel engines and direct injection gasoline engines in stratification mode) * air charge during gas exchange, compression, adding the fuel close to the end of the compression (with the help of injection pump and injection valve)- Mixture compression (characteristic for conventional gasoline engines) * "carburettor ": mixture formation caused by the air flow in the suction pipe * "gasoline injection": pressurized injection into the air flow during intake and/or displacement ill front of the closed intake valve

f) Location where the Fuel is Added

- Interior mixture formation * filling of the cylinder with air via intake ports; separate injection of fuel into the combustion chamber (in the intake stroke or compression stroke); diesel engine, direct injection engine (Dl engine)- Exterior mixture formation * formation of a fuel-air mixture outside of the combustion chamber; conventional gasoline engine

g) Type of Load Control

- Quantity control * the mass of the working fluid that is used for each work cycle will be changed (control of air-fuel-amount) * the composition of the fluid (mixture) remains almost unchanged (conventional gasoline engine, throttle control)- Quality control * the mixture ratio of fuel and air will be changed * the mass of the working fluid per combustion cycle will remain almost constant (diesel engine, direct injection engine at low load; mixture control)

h) Type of Ignition

- External ignition (definition of the gasoline engine) * ignition using a local energy supply from the outside (such as spark ignition with the use of a spark plug)- Self-ignition (definition of the diesel engine) * fuel-air mixture self-ignites due to the high compression temperature

i) Types of processes

- Classical process * gasoline engine and diesel engine with the following characteristics: conventional gasoline engine: - external ignition of the quantity controlled homogeneous mixture diesel engine: - self-ignition of a quality controlled heterogeneous mixture direct injection gasoline engine: - at idle speed and during low part-load, external ignition of the quality controlled heterogeneous mixture; at high part-load and full load, external ignition of the quantity controlled mixture

- Hybrid processes * combination of the characteristics of gasoline and diesel engine

- Special processes * Examples: steam engine, Stirling engine

j) Type of Cooling- Air cooling (direct cooling) * ambient air is directed over the engine surface, which is usually finned- Fluid cooling (indirect cooling): * the engine -transfers heat to the coolant (usually water) as a subcarrier * better heat transfer makes the fins for cooling surfaces unnecessary- auxiliary devices that are most often needed: * cooling fan (air and fluid cooling) * radiator and cooling-water pump (fluid cooling)

A - Air Cooled Using Fins B – Cobination of Air and Fluid

k) Type of Piston Motion

- reciprocating engine * performs a reversing motion- Rotary piston engine * performs a continuous motion, e.g., rotary engine

I) Type of Cylinder Arrangement

- number of cylinders in a row limited by the installable length and admissible vibrational stress of the crankshaft, therefore cylinders are often arranged in several rows and in various positions

Basic Engine Components:

Crankshaft

Connecting Rod

Piston Valve Train

Camshaft