Introduction to MPFI

INTRODUCTION:

•  MPFI stands for MULTI POINT FUEL INJECTION. 
• It is an improvement over carburetors. It allows more efficient combustion of fuel, thereby producing more power with lesser emissions. 
• It is a technology similar to what CRDI is in diesel engines.

NEED FOR MPFI:

•  In carburetor, air and fuel are mixed in a fixed ratio and sent to the cylinders for combustion. 
• This is a purely mechanical system with negligible flexibility.
•  It often sends more fuel into the cylinder than the available air, thereby leading to incomplete combustion, high fuel consumption and excess emissions. 
• This also leads to carbon deposits inside the combustion chamber and reduces engine life.

BASIC CONCEPT:

•  MPFI is an intelligent way of doing what a carburetor does.
•  In this system each cylinder has injectors to spray the fuel/air charge into the cylinders. 
• The fuel and air are mixed in what is called the intake manifold. 
• In MPFI, each injector in controlled by the ECU.
•  The ECU monitors various engine parameters and accordingly decides just how much fuel is to be injected into the cylinder and at precisely what time .
•  This system also allows each cylinder to be controlled independently.

TYPES OF MPFI SYSTEMS:

 The various types of MPFI systems are: 

1. Simuntaneous : Together in all the cylinders. 

2. Sequential : Direct injection into the individual cylinders against their power strokes.

 3. Group : In cylinder pairs [in V engines]

TYPES OF MPFI SYSTEMS:

 Choosing the correct technique according to the engine configuration results in: - better power balance between cylinders - higher output from each cylinder - faster throttle response Of these technologies, sequential gives the best combination of power balance and output in inline 4 cylinder engines.

ADVANTAGES OF MPFI:

 (1) More uniform A/F mixture will be supplied to each cylinder, hence the difference in power developed in each cylinder is minimum.

 (2)Vibration from the engine equipped with this system is less, due to this the life of engine components is improved. 

(3) No need to crank the engine twice or thrice in case of cold starting as happens in the carburettor system. (4) Immediate response, in case of sudden acceleration / deceleration. 

(5) Since the engine is controlled by ECU, more accurate amount of A/F mixture will be supplied and as a result complete combustion will take place. This leads to effective utilization of fuel supplied and hence low emission level. 

(6) The mileage of the vehicle will be improved.

INJECTORS:

•  These are precision built solenoid valves. 
• They have single or multiple orifices which spray fuel into the intake manifold. 
• The fuel is taken from a common rail/header, pressurized to around 3 bar, fed by a high pressure fuel pump.

INJECTOR CARE:

INJECTOR CARE Fuel injectors can get clogged by olefin wax, water, dirt and other debris material present in the fuel or in the intake manifold. As such they require some basic maintenance and periodic cleaning. - Regular service of vehicle at specified intervals - Use of unadulterated and recommended grade fuel - Use of specialized injector cleaner additives - Periodic cleaning of injectors on injector cleaning machine.

ECU:

ECU ECU or the Electronic Control Unit is the brain behind the MPFI system. It is a computer chip which receives input on various engine parameters, compares them against preloaded engine and throttle maps and accordingly decides exactly how much fuel is to be injected into which cylinder and at what time

ECU:

ECU Because of this, the engine becomes more cleaner, more responsive and uses lesser fuel. Modern ECUs have memory by which they can learn the user’s driving style. For e.g., if someone has a habit of speedy pick up, the ECU will remember that and give more power at lower rpm by injecting in more fuel. It will judge by the amount of pressure being put of the throttle.

 The various parameters monitored by the ECU are: 

Ambient temperature 

Coolant temperature 

Exhaust temperature 

Exhaust Oxyzen content 

Inlet manifold vacuum 

Throttle position

 Engine rpm 

Vehicle road speed 

Crankshaft position 

Camshaft position

 Outside air pressure 

Pressure on throttle

ECU CHIPPING:

•  Manufactures program the ECU for general use keeping in mind fuel efficiency, engine life, service intervals fuel quality and diverse usage conditions. 
• The engines are made to develop only a fraction of the output which they actually can produce. ECU Chipping refers to modifying the original ECU programming to alter the way it reacts to certain inputs, in order to maximize engine performance

 This is done to change engine power and torque, performance characteristics at a particular rpm, engine rpm limit, road speed limit, engine timing etc. Chipping can be done either by overriding the original ECU with a specially designed one or by simply remapping the original ECU as per requirement.

 By chipping the ECU, we can significantly increase the engine’s power and torque and rpm limit for drag races etc. 

We can change the mapping to improve pick up in a particular rpm range, like for reducing turbo lag. We can get custom maps developed for our own driving style. 

Commercial vehicles can be fitted with speed limiters and be mapped for torque and reduced rpm in interest of safety and to boost engine life and economy.

Basic Terms Of Internal Combustion engines/EME

        APPLICATIONS OF INTERNAL COMBUSTION ENGINES

1.     Automotive:   (i)     Car

                                       (ii)    Truck/Bus

                                            (iii)   Off-highway

2.        Locomotive

3.        Light Aircraft

4.        Marine:  (i)    Outboard

                                  (ii)   Inboard

                                  (iii)  Ship

5.        Power Generation:   (i)    Portable (Domestic)

                                               (ii)   Fixed (Peak Power)

6.        Agricultural:             (i)    Tractors

                                     (ii)    Pump sets

7.        Earthmoving:  (i)     Dumpers

                                      (ii)   Tippers

                                      (iii)  Mining Equipment

8.        Home Use:   (i)      Lawnmowers

                                    (ii)     Snow blowers

                                    (iii)    Tools

9.        Others

BASIC TERMS REGARDING ENGINES

01)Bore

The inside Diameter of the Cylinder is known as the Bore and it is measured in millimeter (mm).

02)  Stroke

It is the distance travelled by the Piston from one of its dead centre position to the other dead centre position.

03) Dead Centre

They corresponds to the positions occupied by the piston at the end of its Stroke,where the centre line of the Connecting Rod and Crank are in the same straight line.For Vertical Engines these are known as Top Dead Centre (T.D.C) and Bottom Dead Centre (B.D.C) position.In Horizontal Engines,these are known as Inner Dead Centre (I.D.C) and Outer Dead Centre (O.D.C) position.

04)  Top Dead Centre

In Vertical Engines,the top most position of the Piston towards the cover end side of the cylinder is known as Top Dead Centre.

05)  Bottom Dead Centre

In Vertical Engines,the lower position of the Piston towards the Crank end side of the cylinder is known as Bottom Dead Centre.

06)  Piston Displacement

It is also known as "Swept Volume".It is the volume through which the Piston sweeps for its one Stroke.It is equal to the Area of cross section of the Piston multiplied by its Stroke Length.

07)  Clearance Volume

It is the Volume included between the Piston and the Cylinder Head when the Piston is at its Top Dead Centre in Vertical Engines and inner Dead Centre in Horizontal Engines.The Clearance Volume is generally expressed as percentages of Swept Volume.

08)  Compression Ratio

It is the ratio of the total Cylinder Volume to the Clearance Volume.For Petrol Engines the value of Compression Ratio is varies from 5:1 To 9:1 and for Diesel Engines varies from 14:1 To 22:1

09)  Piston Speed

It is the distance travelled by the Piston in one minute.The piston Speed=2LN meter/min.If the R.P.M. of Engine Shaft=N and length of Stroke=L meter.

10) Crank Throw

This is the distance between the Centre of Crankshaft and Centre of Crank Pin.The distance will be equal to half the Stroke Length

11)  Carburetion

The process of breaking up the fuel into minute particles and mixing it with air is called "Carburetion". This process is mostly used in the internal combustion engine, which have low compression ratio and which use highly volatile liquid fuels such as petrol. The process of breaking up fuel in minute particles is known as "Atomization". Carburettor is the device where all the carburetion takes place.

12)  Scavenging

The process of removing burnt exhaust gases from the combustion chamber of the engine cylinder is known as "Scavenging". In four-stroke cycle engine, the piston pushes the burnt gases to exhaust manifold during its exhaust stroke. In the two-stroke cycle engine a blast of fresh charge is made to enter at higher velocity into a combustion chamber at the end of working stroke and thus drives out burnt exhaust gases.

13) Compensation

The process of providing additional fuel or reducing the fuel by certain means to correct the mixture strength to meet the varying nature of speeds and load on the engines is known as "Compensation". This process is mostly used in simple carburettor specially used for automotive purposes.

14) Firing Order

The sequences in which firing or power impulses occur in an internal combustion engine are called "Firing Order". The firing order should be such that there is always a proper balance and it does not cause vibrations.

15) Detonation

Some sudden and violent knocks are experienced in internal combustion engine at sometimes. This knocks are known by "Detonation". This knock is set up by a high pressure wave giving a loud pulsating noise as it strikes against the cylinder walls, cylinder head and piston. It should be noted that detonation is not pre-ignition but something, which occur after the spark, has started the ignition.

16) Doping

The process of adding small quantity of Tetraethyl lead to suppressed the detonation in petrol engine is called "Doping". If the tetraethyl lead used in large proportion, there are chances of engine damage due to deposition of lead oxide in the combustion chamber.

17) Diesel Knock

A high pressure wave set up in compression ignition engine (Diesel Engine), which causes knocks. This knock is called as "Diesel knock". It badly affects the engine efficiency and power drop; also engine runs very rough due to diesel knock.

18) Dissociation

If a gas or mixture of gases is heated to very high temperature, the vibrating molecules of different gases make violent encounters resulting in splitting up of the compound molecules into smaller molecules which recombine to form their compound molecules as the temperature lowered. The phenomenon is called "Dissociation". The dissociation is mainly due to breaking up of carbon dioxide into carbon monoxide and oxygen.

19) Supercharging

The process of increasing the weight or density of air-fuel mixture or compressed air, induced into the cylinder during the induction stroke is known as "Supercharging". This is achieved by a separate compressor and known as supercharger or blower.

20) Turbulence

When the atomised fuel injected into the combustion chamber of compression ignition engine may be burnt efficiently there should be a high relative velocity between the air and fuel so that a thorough mixing takes place. This is achieved by "Turbulence".

GENERAL VIEW OF AN ENGINE

CLASSIFICATION OF INTERNAL COMBUSTION ENGINES

  

 -Based on motion, no. of cylinders & arrangement

1. Reciprocating:  (a)   Single Cylinder

                                  (b)  Multi-cylinder (I)     In-line

                                                                        (ii)     V

                                                                     (iii)     Radial

                                                                     (iv)    Opposed Cylinder

                                                                     (v)     Opposed Piston

2. Rotary:                         (a)   Single Rotor

                                             (b)   Multi-rotor

                          

                         - Based on no. Of strokes per cycle

1.Four Stroke Cycle:                (a) Naturally Aspirated

                                                        (b)Supercharged/Turbocharged

2.Two Stroke Cycle:                 (a)  Crankcase Scavenged

                                                        (b) Uniflow Scavenged

                                                                (i)   Inlet valve/Exhaust Port

                                                                (ii)  Inlet Port/Exhaust Valve

                                                                (iii) Inlet and Exhaust Valve

                                 

                               

                              -  Based on  Operating Cycle

1)  Otto (For the Conventional SI Engine)

2)  Diesel (For the Ideal Diesel Engine)

3)    Dual (For the Actual Diesel Engine)

                                    

- Based on cooling

1)    Water cooled engines

2)    Air cooled engines

    

                -  Based on type of ignition

1)     Spark ignition engine

2)     Compression ignition engine

                         -Based on fuel used

1)    Petrol engines

2)    Diesel engines

3)    Gas engines

                   CLASSIFICATION IN DETAIL

-Based on motion, no. of cylinders & arrangement

1. Reciprocating:  (a)   Single Cylinder

                                  (b)  Multi-cylinder (I)     In-line

                                                                        (ii)     V

                                                                     (iii)     Radial

                                                                     (iv)    Opposed Cylinder

                                                                     (v)     Opposed Piston

2. Rotary:                         (a)   Single Rotor

                                             (b)   Multi-rotor

-   Reciprocating Engines

A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. There may be one or more pistons. Each piston is inside a cylinder, into which a gas is introduced, either already hot and under pressure (steam engine), or heated inside the cylinder either by ignition of a fuel air mixture (internal combustion engine) or by contact with a hot heat exchanger in the cylinder .The hot gases expand, pushing the piston to the bottom of the cylinder. The piston is returned to the cylinder top (Top Dead Centre) either by a flywheel or the power from other pistons connected to the same shaft. In most types the expanded or "exhausted" gases are removed from the cylinder by this stroke. The exception is the Stirling engine, which repeatedly heats and cools the same sealed quantity of gas.

In all types, the linear movement of the piston is converted to a rotating movement via a connecting rod and a crankshaft or by a swash plate. A flywheel is often used to ensure smooth rotation. The more cylinders a reciprocating engine has, generally, the more vibration-free (smoothly) it can operate. The power of a reciprocating engine is proportional to the volume of the combined pistons' displacement.
A seal needs to be made between the sliding piston and the walls of the cylinder so that the high pressure gas above the piston does not leak past it and reduce the efficiency of the engine. This seal is provided by one or more piston rings. These are rings made of a hard metal which are sprung into a circular groove in the piston head. The rings fit tightly in the groove and press against the cylinder wall to form a seal.
                   The bore/stroke ratio is the ratio of the diameter of the piston, or "bore", to the length of travel within the cylinder, or "stroke". If this is around 1 the engine is said to be "square", if it is greater than 1, i.e. the bore is larger than the stroke; it is "over square". If it is less than 1, i.e. the stroke is larger than the bore; it is "under square".

- ROTARY ENGINES

The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it. Its main application was in aviation, although it also saw use in a few early motorcycles and cars.

(a)   Single Rotor

(b)   Multi-rotor

Wankel Engine Parts

                  In the basic single-rotor Wankel engine, the oval-like epitrochoid-shaped housing surrounds a rotor which is triangular with bow-shaped flanks (often confused with a Reuleaux triangle, a three-pointed curve of constant width, but with the bulge in the middle of each side a bit more flattened). The theoretical shape of the rotor between the fixed corners is the result of a minimization of the volume of the geometric combustion chamber and a maximization of the compression ratio, respectively. The symmetric curve connecting two arbitrary apexes of the rotor is maximized in the direction of the inner housing shape with the constraint not to touch the housing at any angle of rotation (an arc is not a solution of this optimization problem).
The central drive shaft, called the eccentric shaft or E-shaft, passes through the center of the rotor and is supported by fixed bearings. The rotors ride on eccentrics (analogous to cranks) integral with the eccentric shaft (analogous to a crankshaft). The rotors both rotate around the eccentrics and make orbital revolutions around the eccentric shaft. Seals at the corners of the rotor seal against the periphery of the housing, dividing it into three moving combustion chambers. The rotation of each rotor on its own axis is caused and controlled by a pair of synchronizing gears^. A fixed gear mounted on one side of the rotor housing engages a ring gear attached to the rotor and ensures the rotor moves exactly 1/3 turn for each turn of the eccentric shaft. The power output of the engine is not transmitted through the synchronizing gears. The force of gas pressure on the rotor (to a first approximation) goes directly to the center of the eccentric, part of the output shaft.

-Based on no. Of strokes per cycle

1.Four Stroke Cycle:                (a) Naturally Aspirated

                                                        (b)Supercharged/Turbocharged

2.Two Stroke Cycle:                 (a)  Crankcase Scavenged

                                                        (b) Uniflow Scavenged

                                                                (i)   Inlet valve/Exhaust Port

                                                                (ii)  Inlet Port/Exhaust Valve

                                                                (iii) Inlet and Exhaust Valve

-Four Stroke & Two stroke

Today, internal combustion engines in cars, trucks, motorcycles, aircraft, construction machinery and many others, most commonly use a four-stroke cycle. The four strokes refer to intake, compression, combustion (power), and exhaust strokes that occur during two crankshaft rotations per working cycle of the gasoline engine and diesel engine.

The cycle begins at Top Dead Center (TDC), when the piston is farthest away from the axis of the crankshaft. A stroke refers to the full travel of the piston from Top Dead Center (TDC) to Bottom Dead Center (BDC). (See Dead centre.)

1. INTAKE stroke: On the intake or induction stroke of the piston, the piston descends from the top of the cylinder to the bottom of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close.

2. COMPRESSION stroke: With both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the fuel-air mixture. This is known as the compression stroke.

3. POWER stroke.: While the piston is close to Top Dead Center, the compressed air–fuel mixture is ignited, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a diesel cycle or compression ignition engine). The resulting massive pressure from the combustion of the compressed fuel-air mixture drives the piston back down toward bottom dead center with tremendous force. This is known as the power stroke, which is the main source of the engine's torque and power.

4. EXHAUST stroke.: During the exhaust stroke, the piston once again returns to top dead center while the exhaust valve is open. This action evacuates the products of combustion from the cylinder by pushing the spent fuel-air mixture through the exhaust valve(s).

Two-stroke Engine

A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crank shaft (an up stroke and a down stroke of the piston, compared to twice that number for a four-stroke engine). This is accomplished by using the beginning of the compression stroke and the end of the combustion stroke to perform simultaneously the intake and exhaust (or scavenging) functions. In this way two-stroke engines often provide strikingly high specific power, at least in a narrow range of rotations speeds. The functions of some or all of the valves of a four stroke engine are usually served by ports that are opened and closed by the motion of the pistons, greatly reducing the number of moving parts. Gasoline (spark ignition) versions are particularly useful in lightweight (portable) applications such as chainsaws and the concept is also used in diesel compression ignition engines in large and non-weight sensitive applications such as ships and locomotives.

                    -  Based on  Operating Cycle

1)  Otto (For the Conventional SI Engine)

2)  Diesel (For the Ideal Diesel Engine)

3)  Dual (For the Actual Diesel Engine)

  OTTO (FOR THE CONVENTIONAL S.I. ENGINE)

The idealized four-stroke Otto cycle p-V diagram: the intake (A)  stroke is performed by an isobaric expansion, followed by an adiabatic  compression (B)  stroke. Through the combustion of fuel, heat is added in an isochoric process, followed by an adiabatic expansion process, characterizing the power (C)  stroke. The cycle is closed by the exhaust (D)  stroke, characterized by isochoric cooling and isobaric compression processes.

An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical reciprocating piston engine. The Otto cycle is constructed out of:

1.     TOP and BOTTOM of the loop: a pair of quasi-parallel adiabatic processes

2.     LEFT and RIGHT sides of the loop: a pair of parallel isochoric processes

The adiabatic processes are impermeable to heat: heat flows into the loop through the left pressurizing process and some of it flows back out through the right depressurizing process, and the heat which remains does the work.
The Otto cycle consists of adiabatic compression, heat addition at constant volume, adiabatic expansion, and rejection of heat at constant volume. In the case of a four-stroke Otto cycle, technically there are two additional processes: one for the exhaust of waste heat and combustion products (by isobaric compression), and one for the intake of cool oxygen-rich air (by isobaric expansion); however, these are often omitted in a simplified analysis. Even though these two processes are critical to the functioning of a real engine, wherein the details of heat transfer and combustion chemistry are relevant, for the simplified analysis of the thermodynamic cycle, it is simpler and more convenient to assume that all of the waste-heat is removed during a single volume change.

DIESEL (FOR THE IDEAL DIESEL ENGINE)

• Process 1 to 2 is isentropic compression (blue)
• Process 2 to 3 is reversible constant pressure heating (red)
• Process 3 to 4 is isentropic expansion (yellow)
• Process 4 to 1 is reversible constant volume cooling (green)

The Diesel is a heat engine: it converts heat into work. The isentropic processes are impermeable to heat: heat flows into the loop through the left expanding isobaric process and some of it flows back out through the right depressurizing process, and the heat that remains does the work.

• Work in (W_in) is done by the piston compressing the working fluid
• Heat in (Q_in) is done by the combustion of the fuel
• Work out (W_out) is done by the working fluid expanding on to the piston (this produces usable torque)
• Heat out (Q_out) is done by venting the air

- Based on cooling

-Water cooled engines

  -Air cooled engines

-WATER COOLED ENGINES

Liquid cooling is also employed in maritime vehicles. For vessels, the seawater itself is mostly used for cooling. In some cases, chemical coolants are also employed (in closed systems) or they are mixed with seawater cooling. Water cooling is used in those engines where more cooling effect is required. Most modern internal combustion engines are cooled by a closed circuit carrying liquid coolant through channels in the engine block, where the coolant absorbs heat, to a heat exchanger or radiator where the coolant releases heat into the air. Thus, while they are ultimately cooled by air, because of the liquid-coolant circuit they are known as water-cooled

-AIR COOLED ENGINES

Heat generated by an air-cooled engine is released directly into the air. Typically this is facilitated with metal fins covering the outside of the cylinders which increase the surface area that air can act on.
In all combustion engines, a great percentage of the heat generated (around 44%) escapes through the exhaust, not through either a liquid cooling system nor through the metal fins of an air-cooled engine (12%). About 8% of the heat energy finds its way into the oil, which although primarily meant for lubrication, also plays a role in heat dissipation via a cooler

              -  Based on type of ignition

1)     Spark ignition engine

2)     Compression ignition engine

-SPARK IGNITION ENGINE

The term spark-ignition engine normally refers to internal combustion engines, specifically petrol engines, where the initiation of the combustion process of the air-fuel mixture is ignited within the combustion chamber by a spark from a spark plug. The term contrasts with diesel-fueled compression-ignition engines, where the heat generated from compression is enough to initiate the combustion process.

          -COMPRESSION IGNITION ENGINE

A diesel engine (also known as a compression-ignition engine and sometimes capitalized as Diesel engine) is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. This is in contrast to spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which uses a spark plug to ignite an air-fuel mixture. The diesel engine is modeled on the Diesel cycle.

                        The diesel engine has the highest thermal efficiency of any regular internal or external combustion engine due to its very high compression ratio. Low-speed diesel engines (as used in ships and other applications where overall engine weight is relatively unimportant) often have a thermal efficiency which exceeds 50 percent.

                          -Based on fuel used

1) Petrol engines

  2) Diesel engines

 3) Gas engines

   PETROL ENGINES

                       A petrol engine (known as a gasoline engine in North America) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels.
It differs from a diesel engine in the method of mixing the fuel and air, and in the fact that it uses spark plugs to initiate the combustion process. In a diesel engine, only air is compressed (and therefore heated), and the fuel is injected into the now very hot air at the end of the compression stroke, and self-ignites. In a petrol engine, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection).
The pre-mixing was formerly done in a carburetor, but now (except in the smallest engines) it is done by electronically controlled fuel injection. Petrol engines run at higher speeds than Diesels partially due to their lighter pistons, conrods & crankshaft (as a result of lower compression ratios) & due to petrol burning faster than diesel. However the lower compression ratios of a petrol engine gives a lower efficiency than a diesel engine.

DIESEL ENGINES

A diesel engine (also known as a compression-ignition engine and sometimes capitalized as Diesel engine) is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. This is in contrast to spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which uses a spark plug to ignite an air-fuel mixture.

The fuel injector ensures that the fuel is broken down into small droplets, and that the fuel is distributed evenly. The heat of the compressed air vaporizes fuel from the surface of the droplets. The vapour is then ignited by the heat from the compressed air in the combustion chamber, the droplets continue to vaporize from their surfaces and burn, getting smaller, until all the fuel in the droplets has been burnt. The start of vaporization causes a delay period during ignition, and the characteristic diesel knocking sound as the vapor reaches ignition temperature and causes an abrupt increase in pressure above the piston. The rapid expansion of combustion gases then drives the piston downward, supplying power to the crankshaft. Engines for scale-model aero planes use a variant of the Diesel principle but premix fuel and air via a carburetion system external to the combustion chambers.

GAS ENGINES

A gas engine means an engine running on a gas, such as coal gas, producer gas biogas, landfill gas, or natural gas. Generally the term gas engine refers to a heavy duty, slow revving industrial engine capable of running continuously at full output for periods approaching a high fraction of 8,760 hours per year, for many years, with indefinite lifetime, unlike say a gasoline automobile engine which is lightweight, high revving and typically runs for no more than 4,000 hours in its entire life. Typical power ranges from 10 kW to 4,000 kW.