Part 1: Squish from piston
After the piston squeezes the air-fuel mixture, the spark ignites it and causes combustion. The expansion of the combustion gases pushes the piston downward during the power stroke. There are various types of chamber and we are going to study the effect of spark-plug location & squish on the Chevy 302 engine.
Modifying the piston is the most common way to generate a squish-piston engine because it is the most convenient item to be manufactured.
The above pistons create squish in different levels. The piston on the left is a flat-top piston that kills most of the quench effect. The middle piston shows a half-dished nature. It makes use of a dish to lower the local compression but maintaining the flat portion to trigger a quench effect. The domed piston (RHS) increases compression ratio but still retains a flat portion for the quench effect. The squish improves the dyno performance because the turbulence enhances air-fuel mixing, heat transfer of cylinder wall and thermal efficiency.
Part 2: Open vs closed wedge
Chamber design can make a remarkable effect on combustion efficiency and power. The closed-wedge combustion chamber produces more horsepower than the open-wedge combustion chamber because the asymmetric area in a wedge-shaped chamber creates turbulence when the piston approaches top dead center (TDC). Although turbulence (squish) sounds bad, the opposite is true. If an engine is designed to amplify the squish effect, the piston crown comes very close to the cylinder head at TDC. The gases are suddenly "squished" out within the combustion chamber due to the modified shape. As a consequence, the dyno performance of the closed-wedge system is stronger.
Part 3: Side plug vs center plug
The center plug provides a symmetric thermal distribution so that the heat transfer is more effective. In contrast, the side plug generates a thermal gradient inside the chamber and hence the heat-exchange process is limited.
After the piston squeezes the air-fuel mixture, the spark ignites it and causes combustion. The expansion of the combustion gases pushes the piston downward during the power stroke. There are various types of chamber and we are going to study the effect of spark-plug location & squish on the Chevy 302 engine.
Modifying the piston is the most common way to generate a squish-piston engine because it is the most convenient item to be manufactured.
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| superchevy |
The above pistons create squish in different levels. The piston on the left is a flat-top piston that kills most of the quench effect. The middle piston shows a half-dished nature. It makes use of a dish to lower the local compression but maintaining the flat portion to trigger a quench effect. The domed piston (RHS) increases compression ratio but still retains a flat portion for the quench effect. The squish improves the dyno performance because the turbulence enhances air-fuel mixing, heat transfer of cylinder wall and thermal efficiency.
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| Measurement data |
Part 2: Open vs closed wedge
Chamber design can make a remarkable effect on combustion efficiency and power. The closed-wedge combustion chamber produces more horsepower than the open-wedge combustion chamber because the asymmetric area in a wedge-shaped chamber creates turbulence when the piston approaches top dead center (TDC). Although turbulence (squish) sounds bad, the opposite is true. If an engine is designed to amplify the squish effect, the piston crown comes very close to the cylinder head at TDC. The gases are suddenly "squished" out within the combustion chamber due to the modified shape. As a consequence, the dyno performance of the closed-wedge system is stronger.
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| Example - LHS: open-wedge, RHS: closed-wedge (pantera) |
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| Measurement data: The ignition timings of the these two chambers are fixed at 20 deg (@crank) regardless of RPM values. |
Part 3: Side plug vs center plug
The center plug provides a symmetric thermal distribution so that the heat transfer is more effective. In contrast, the side plug generates a thermal gradient inside the chamber and hence the heat-exchange process is limited.
 |
| Measurement data |