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Top Down ScVENGING

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    By

    EMIL LOUIS

    No. 18

    S7 ME

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    CONTENTSIntroduction

    Advantages of two stroke engine

    LimitationsObjectives of this study

    Engine design

    Operation

    Motored engine tests

    Conclusion

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    INTRODUCTION In the late 1990 the Orbital Engine Company of Australia designed such a two-

    stroke engine for automotive application.

    It was an externally compressed air-scavenging GDI engine that used an air-

    assisted fuel injection system.

    The use of an external compressor allows lubrication similar to that used in four-

    stroke automotive engines.

    Exhaust ports were located at the bottom of the cylinder as with conventionaltwo stroke engines.

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    ADVANTAGES OF THE TWO

    STROKE ENGINEHigh power to weight ratio

    Lighter fly wheel

    Valves and valve springs are absent

    Simple design

    Low manufacturing cost

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    LIMITATIONS Removal of exhaust gases is not efficient.

    Insufficient scavenging results in excessive exhaust gas residual concentration

    that leads to slow, inefficient burning and misfires.

    They also suffer from lower fuel efficiency due to significant amounts of air

    fuel mixture being lost out the exhaust pipe.

    High emissions due to unburned hydrocarbons flowing out the exhaust along

    with the combustion products.

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    STUDY

    This study explores:

    the feasibility of using multiple check valves built into

    the cylinder head, in place of a camshaft driven poppet valve,

    in a topdown uniflow-scavenged engine.

    the possibility of a clean burning engine that could rival

    four-stroke engine emissions.

    to demonstrate the feasibility of the check valve conceptand the basic operation of the engine.

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    ENGINE DESIGN A single-cylinder 1975 Yamaha 400 cc two-

    stroke engine.

    The engine block and cylinder head were

    specially constructed.

    Two diametrically opposed sets of exhaust

    ports are located at the bottom of the cylinder.

    The head contains a matrix of 16 check

    valves.

    Supercharger is used to supply scavenging air

    which is mounted above the intake plenum.

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    Two diametrically opposed set

    of exhaust ports are located atthe bottom of the cylinder.

    Each port consist of four 15 mm

    dia closely spaced round ports.

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    The head contains a matrix of 16 check valves .

    Each valve consist of a 10 mm dia channel opening upto 2.6

    mm long and then a 16 mm cavity.

    The cavity contains 1.5 mm thin ,12.24 mm square steelplates that weighs 1.23 grams.

    A two mm thick stainless steel plate provided at the bottom

    of the head supports platelets from below.

    The retaining plates have a cluster of four 5.5mm dia holes

    for each check valves.

    .

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    Contd The retaining plate has a rectangular slot cut at the center for spark

    plug and fuel injector.

    The platelets are free floating.

    The roots type super charger supply the scavenging air.

    The supercharger mounted to large 3.8 gallon surge tank.

    Fuel injector is operating at a pressure of 75 bar.

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    . Illustration of check valve looking up at the retaining plate.

    (a) Platelet in the optimum orientation for airflow.

    (b) Platelet rotated 45 resulting in a poor orientation for

    airflow.

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    OPERATION

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    MOTORED ENGINE TESTS

    The novel feature of the engine is the completely free operation of thevalves without the use of a cam.

    The valves are not driven off with the cam profile.

    The purpose of this test is to determine the exact timing of operationof inlet valves.

    The method is to use piezoelectric sensers to sense the vibrations .

    Engine speed was 675 rpm.

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    TEST DATA ANALYSIS

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    CONCLUSIONS

    The engine equipped with the novel passive check valve concept was

    successfully operated.

    Fuel efficiency was increased due to the novelty of the engine.

    Opening and closing times of valves is determined from the graph.

    The engine was successfully fired up to a maximum speed of 3600 rpm.

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    REFERENCES G. Ciccarelli, Steve Reynolds, Phillip Oliver- Design and evaluation of the

    ELEVATE two-stroke automotive engine- Mechanical and MaterialsEngineering, Queens University, SAE Paper 2003-01-0403, 2003.

    P. Oliver, S. Reynolds, G. Ciccarelli, Flowbench -Calibration of a numericalmodel for a novel uniflow-scavenged two-stroke GDI engine- SAE Power

    Train Conference, Toronto, 2006.

    Richard Stone-Introduction to IC Engines- MacMillan Press Ltd, 1999.

    J.B. Heywood-Internal Combustion Engine Fundamentals- McGraw-Hill, 1988.

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    Queries?

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