1 / 16

Geometry Vs Engine Breathing

Geometry Vs Engine Breathing. P M V Subbarao Professor Mechanical Engineering Department. Its not engine Volume, but Mass of air Decides the Power Output …. Improper Breathing in an Engine Creates A Pumping Cycle. Anatomy of Intake System.

clydea
Download Presentation

Geometry Vs Engine Breathing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Geometry Vs Engine Breathing P M V Subbarao Professor Mechanical Engineering Department Its not engine Volume, but Mass of air Decides the Power Output ….

  2. Improper Breathing in an Engine Creates A Pumping Cycle

  3. Anatomy of Intake System

  4. The Intake System and Instantaneous Mass of air in Engine Cylinder

  5. Piston Speed Piston Displacement : • The speed of the piston

  6. Mean Piston Speed • Better than using rotational speed (RPM) • Gas flow velocities in the intake manifold and cylinder all scale with mean piston speed. • Should be between 8 and 16 m/sec. • Lower end is typical of large industrial engines • High end is typical of automotive engines

  7. 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.

  8. Effect of Rod Ratio on Piston Speed

  9. Rod Ratio vs. Intake Efficiency • A “R” value of 1.75 is considered “ideal” by some respected engine builders, if the breathing is optimized for the design. • Except for purpose-built racing engines, most other projects are compromises where 1.75 may not produce the best results. • The “R” value can be used as a correction factor to better “match” the intake to the manifold. • Low “R” numbers (1.45 - 1.75) are produced by short rods in relation to the stroke. • High “R” numbers (1.75 - 2.1) are produced by long rods in relation to the stroke.

  10. SHORT ROD : Intake Stroke • Intake Stroke -- Short rod spends less time near TDC and will suck harder on the cylinder head from 10o ATDC to 90o ATDC the early part of the stroke. • Will not suck as hard from 90o ATDC to BDC as a long rod. • Will require a better cylinder head than long rod to produce same peak HP. • Will require stronger wrist pins, piston pin bosses, and connecting rods than a long rod. • Short rod spends more time at the bottom which may reduce intake charge being pumped back out intake tract as valve closes. • May permit longer intake lobe and/or later intake closing than a long rod.

  11. LONG ROD • Intake Stroke -- will draw harder on cylinder head from 90o ATDC to BDC. • Compression Stroke -- Piston travels from BDC to 90o BTDC faster than short rod. • Goes slower from 90o BTDC to TDC--may change ignition timing requirement versus short rod as piston spends more time at top.

  12. http://victorylibrary.com/mopar/rod-tech-c.htm

  13. The Valve and its Inlet Conditions

More Related