Mechanical Losses in An Engine

P M V SubbaraoProfessor

Mechanical Engineering Department

Estimation of Curse…..One-Third of Car Fuel Consumption Is Due to

Friction Loss !!!

Science Daily (Jan. 12, 2012)

• No less than one third of a car's fuel consumption is spent in overcoming friction.

• This friction loss has a direct impact on both fuel consumption and emissions.

• New technology can reduce friction by anything from 10% to 80% in various components of a car, according to a joint study by VTT Technical Research Centre of Finland and Argonne National Laboratory (ANL) in USA.

• It should thus be possible to reduce car's fuel consumption and emissions by 18% within the next 5 to 10 years and up to 61% within 15 to 25 years.

Performance of US Vehicles

Future Targets for LCVs

The Cyclic Integral

dVpW indcycle,

k

NWP cycle

engine

60

k=1:for two-stroke cyclek=2:for four-stroke cycle

Frictional Limit of A Thermodynamic Cycle

• Integration of Real p-V diagram of an engine cycle will give net indicated work output per cycle.

• This is only an indicative work output.• Only a fraction is available for use.• Actual work output available for use is called as engine brake

work output.• Any thermodynamic cycle can be implemented as an engine.• Thermodynamic model generates indicated work output and

engine generates brake work output.• Any thermodynamic concept is said to be practically feasible,

only when engine brake power is positive and significant with respect to physical size of the engine.

• The difference between indicative work output and brake work output is defined as Frictional Work.

• The value of brake or frictional work is practically accepted as significant by comparing to the size of the engine.

Friction Loss

• As the internal parts of an engine move, they rub against each other and lose energy due to friction.  

• The drain of power is the piston rubbing against the cylinder walls.  

• As power output and spin rate increase, the losses due to friction account for a larger portion of the engine's gross output.  

• This is why efficiency falls off above the "sweet spot".  • Oil is circulated in the engine to reduce friction, but the

primary goal is to reduce wear to an acceptable level.  • Until recently, engine design did not go to great lengths to

further reduce friction and as a result improve efficiency.  • Ironically, friction becomes more of a problem as engines

get smaller.  • So, when we make an engine smaller to address the partial

power problem, we give up some of the gain to increased friction losses.

Distribution of Fuel Power

Fuel energy distribution for a medium size passenger car during an urban cycle

Classification of Mechanical Losses

• Internal combustion engines involve mechanical losses due to relative motions among the components such as Piston, crank and valve trains or bearings.

• A mechanical efficiency of internal combustion engine (ICE) is 0% at idling and about 90% at high operating load.

• At the early stage of design, mechanical losses optimization is always a difficult task.

• A model for simulation of mechanical losses and their extrapolation from the known point is required for estimation of mechanical losses.

Distribution of Mechanical Losses

Effect of Speed & Size on Component of Friction

Major Components of IC Engine Friction

• Crank Shaft Friction

• Reciprocating Friction

• Valve train Friction

• Auxiliary component friction

A Stribeck curve :Fundamental Idea to Reduce Friction & Wear

p

N Number Hersey

Challenges in Implementing Optimal Lubrication

Anatomy of Piston Assembly