The Role of Cylinder Geometry on Thermo- mechanical Process in I.C. Engines-2 P M V Subbarao Professor Mechanical Engineering Department Geometry is an Universal Solution of All the Issues….

The Geometrical Description of Engine Cylinder

Define Rod ratio Instantaneous Displacement Volume

Instantaneous Engine Cylinder Volume

Identification of Events Instantaneous compression ratio during compression For a general thermodynamic compression process:

Kinetics of Engine Assembly & Generation of Primary Dynamic Forces

Cylinder Geometry Vs Frictional Losses Engine friction is affected by the bore-to-stroke ratio because of two competing effects: Crankshaft bearing friction and power-cylinder friction. As the bore-to-stroke ratio increases, the bearing friction increases because the larger piston area transfers larger forces to the crankshaft bearings. However, the corresponding shorter stroke results in decreased power-cylinder friction originating at the ring/cylinder interface.

The Loss of Valuable Earnings ….. Non-dimensional Frictional Loss

Geometry Vs Engine Heat Transfer

Energy Audit of Conventional S.I. Engine Indicative Cycle at Design Conditions Net Indicative work per cycle : J Fuel Energy Input (J): J & Total cooling loss J Heat transfer density (W/cm²) at......cylinder head: piston upper face: cylinder wall: Effective torque (Nm): 110.0

Instantaneous Heat Transfer (loss) form Cylinder

Gas to Surface Heat Transfer Heat transfer to walls is cyclic. Gas temperature T g in the combustion chamber varies greatly over and engine cycle. Coolant temperature is fairly constant. Heat transfer from gas to walls occurs due to convection & radiation. Convection Heat transfer: Radiation heat transfer between cylinder gas and combustion chamber walls is

Cylinder Surface Area at any Crank Angle

Shapes of Piston Heads

Shapes of Cylinder Heads

Instantaneous Cylinder Surface Area

The Heat Transfer Dictates !!!!!! B/L= 1.4 B/L= 1.0 B/L= 0.7

Cooling of Piston

Ability to Transfer Heat : A Signature of Survival Due to the increased piston- and head surface area, the heat loss increases as the bore/stroke-ratio is increased excessively. These characteristics favor higher engine speeds, over-square engines are often tuned to develop peak torque at a relatively high speed. Due to the decreased piston- and head surface area, the heat loss decreases as the bore/stroke-ratio is decreased. These characteristics favor lower engine speeds and use of poor quality fuels with low running cost.

Geometry Vs Engine Breathing

Improper Breathing in an Engine Creates A Pumping Cycle

Cylinder Geometry Vs Breathing Issues The smaller bore reduces the area available for valves in the cylinder head, requiring them to be smaller or fewer in number. These factors favor lower engine speeds, under-square engines are most often tuned to develop peak torque at relatively low speeds. An under-square engine will typically be more compact in the directions perpendicular to piston travel but larger in the direction parallel to piston travel. An over-square engine allows for more and larger valves in the head of the cylinder.

Instantaneous Piston Speed

Effect of Rod Ratio on Piston Speed

Instantaneous Piston Acceleration

Extreme Limits of R BS The extremes to bore-to-stroke ratio is the inertial forces origination from the piston motion. To achieve high power density, the engine must operate at a high engine speed (up to 18,000 rpm for the Formula 1 engine), which leads to high inertial forces that must be limited by using a large bore-to-stroke ratio. For applications that demand high efficiency, a small bore- to-stroke ratio is necessary and, again because of the inertial forces of the piston, requires a slower engine speed and lower power density. For the marine application that has a 2.5 m stroke, the engine speed is limited to 102 rpm.

The World Largest I C Engine Despite the green hype, internal-combustion engines will keep powering vehicles for the foreseeable future.

The Latest News The world’s biggest engine is the Wärtsilä-Sulzer RTA96. It’s the largest internal combustion engine ever built by man. Wärtsilä-Sulzer RTA96-C is a 14-cylinder, turbocharged diesel engine that was specially designed to power the Emma Maersk which is owned by the Danish Maersk. Wärtsilä-Sulzer RTA96, the world’s biggest engine, has a weight of 2.3 million kilogrammes. If the weight of the average adult person is 70 kgs, this world’s biggest engine has a weight equivalent to the weight of 33,000 people.

Wärtsilä-Sulzer RTA96-C

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Cylinder Geometry Vs Thermo-chemistry Otto developed a cycle assuming that the fuel burns at rates which result in constant volume top dead center combustion. Diesel developed a cycle assuming that the fuel burns at rates which result in constant pressure combustion. Later it was realized that in an actual engine pressure and temperature profile data do not match these simple models. A more realistic modeling namely, Finite Rate Heat Release Model was innovated. Finite Heat Release Model is a Geometric representation of rate of combustion suitable for SI and CI engines. This geometric model can generate more information about the role of engine kinematics.

Real Cumulative Mass Fraction Burning Curve in an Engine

The Ultimate Effect…….

Need for Flexibility in Engine Kinematics Field level Requirements of Otto’s Cycle:

Kinematics of Unconventional Piston Movement

Optimum Cylinder Geometry Identification of the optimum engine geometry that provides the best opportunity to have a highly efficient internal combustion engine is the first step in designing an engine. In-cylinder simulations have shown that the heat transfer increases rapidly above a bore-to-stroke ratio of about 0.5. Engine systems simulations have shown that the pumping work increases rapidly above a bore-to-stroke ratio of about Engine friction models have shown that the crankshaft bearing and power-cylinder friction values, for the most part, cancel each other out for our opposed-piston, two- stroke engine.

The Dilemma of the Classical Engine Kinematics 1. High efficiency requires high expansion ratio 2. High power density requires low compression ratio BUT UNFORTUNATELY Expansion ratio = Compression ratio

How can we change a “ BUT UNFORTUNATELY  “ into an “ AND FORTUNATELY > ” ?

In 2000, a new engine is born...

The software design...

The hardware manufacturing...

The New p-v Diagram

Six Stroke Engine Velozeta Six-stroke engine German Charge pump Crower six stroke engine Griffin six stroke engine Velozeta six-stroke engine Bajulaz six stroke engine

Macro Geometrical Parameters to be selected Engine Cylinder Volume: V Bore & Stroke of the cylinder: (B/L). Connecting Rod length Vs Crank radius (l/a). Engine Compression Ratio : (V d /V c +1).

Cylinder Geometry Vs Frictional Losses Engine friction is affected by the stroke-to-bore ratio because of two competing effects: Crankshaft bearing friction and power-cylinder friction. As the bore-to-stroke ratio increases, the bearing friction increases because the larger piston area transfers larger forces to the crankshaft bearings. However, the corresponding shorter stroke results in decreased power-cylinder friction originating at the ring/cylinder interface.

Cylinder Geometry Vs Thermo-chemistry Otto developed a cycle assuming that the fuel burns at rates which result in constant volume top dead center combustion. Diesel developed a cycle assuming that the fuel burns at rates which result in constant pressure combustion. Later it was realized that in an actual engine pressure and temperature profile data do not match these simple models. A more realistic modeling namely, Finite Rate Heat Release Model was innovated. Finite Heat Release Model is a Geometric representation of rate of combustion suitable for SI and CI engines. This geometric model can generate more information about the role of engine kinematics.

Need for Flexibility in Engine Kinematics Field level Requirements of Otto’s Cycle:

The Ultimate Effect…….

Optimum Cylinder Geometry Identification of the optimum engine geometry that provides the best opportunity to have a highly efficient internal combustion engine is the first step in designing an engine. In-cylinder simulations have shown that the heat transfer increases rapidly above a bore-to-stroke ratio of about 0.5. Engine systems simulations have shown that the pumping work increases rapidly above a bore=to- stroke ratio of about Engine friction models have shown that the crankshaft bearing and power-cylinder friction values, for the most part, cancel each other out for our opposed-piston, two-stroke engine.

Development of Comprehensive Mathematical Templates for I.C. Engines Modeling of IC engine process can be carried out in many ways. Multidimensional, Transient Flow and heat transfer Model. Thermodynamic Transient Model USUF. Fuel-air Thermodynamic Model