Real I. C. Engines Vs Ideal Models P M V Subbarao Professor Mechanical Engineering Department Ideal Cycles Set Performance Limits !!! Real Engines are Yet Reach these Limits…

Need Vs Innovation

Future Targets for LCVs US:LDV:49.1 Japan:55.1 EU:60.6

Gap in Conventional Concepts - factor of 2 in efficiency  Ideal Otto cycle engine with CR = 8: 52%  Real engine: %  Differences because of Throttling losses Heat losses Friction losses

Space for innovation - infinite in pollutants non-equilibriumPollutants are a non-equilibrium effect Burn: Fuel + O 2 + N 2  H 2 O + CO 2 + N 2 + CO + UHC + NO On A Faster Expansion: CO + UHC + NO “frozen” at high level With slow expansion, no heat loss: CO + UHC + NO  H 2 O + CO 2 + N 2 But how to slow the expansion and eliminate heat loss? Worst problems: cold start, transients, old or out-of-tune vehicles. 90% of pollution generated by 10% of vehicles !!!!

Space for innovation - very little in power  IC engines are air processors  Fuel takes up little space  Air flow = power  Limitation on air flow due to  “Choked” flow past intake valves  Friction loss, mechanical strength - limits RPM  Slow burn  Majority of power is used to overcome air resistance  Majority of power is used to overcome air resistance - smaller, more aerodynamic vehicles beneficial

Clues for Improvement- alternative fuels : Natural Gas Somewhat cleaner than gasoline, non-toxic High octane without refining or additives (≈ 110) No cold start problem Half the CO 2 emission of EVs charged with coal- generated electricity Dual-fuel (gasoline + natural gas) easily accommodated Lower energy storage density (≈ 1/4 gasoline) Lower power (≈ 7% less) Attractive for fleet vehicles with limited territory Renewable bio-methane could increasingly take the place of fossil-fuel gas. The IC Engine is not addicted to fossil fuels …. WE ARE!

Clues for Improvement - alternative fuels – Alcohols/Bio-Diesels  Slightly cleaner than gasoline  High octane (≈ 95)/ varying (48 – 67) Cetane  Not cost-effective without price subsidy  Lower storage density (methanol ≈ 1/2 gasoline)  Toxic combustion products (aldehydes) Attractive to farm states

Clues for Improvement- alternative fuels - Hydrogen Ultimate clean fuel Excellent combustion properties Ideal for fuel cells Very low storage density (1/10 gasoline) Need to manufacture - usually from electricity + H 2 O Attractive when we have unlimited cheap clean source of electricity and breakthrough in hydrogen storage technology

What to be learnt to Understand the reasons behind all said so far?!?!?! Geometric & Kinematic Models Used in Current An I.C. Engines

Displacement Work Devices for Execution of Macro Thermodynamic Operations Intake Stroke Power Stroke Compression Stroke Combustion Products Exhaust Stroke

Nature of Temporally Cycling Devices The thermal operation of an IC engine is a transient cyclic process. Even at constant load and speed, the value of in-cylinder thermodynamic parameters vary with time. Each event may get repeated again and again. So, an IC engine operation is a transient process which gets completed in a known or required Cycle time. Higher the speed of the engine, lower will be the Cycle time. How to fix the cycle time? Within a given cycle time, how to allocate the time slots for each process? Within a given time slot, how to control the process speed and hence rates of changes in thermodynamic properties?

The Art of Positive Displacement Work Displacement of system provokes the process. The rate of change in instantaneous controls, decides the rates of changes of other thermodynamic variables. The brain of an animal controls the strain rates in Muscles….. How to design the basic brain of these devices?

Control Dominates the Strength