Meeting Target Swirl Ratio with Minimum Cylinder Head Changes
The client is a leading Indian manufacturer of engines for use in automotive and off-highway industries.
How to Meet Target Swirl Ratio with Minimum Cylinder Head Changes
Clients wanted to modify the swirl ratio of one of their engines as part of their strategy to meet the new emissions norms. They needed to achieve this with minimum changes to the head so as to minimise costs.
Client engaged Caepro to make design modifications to the head that would give them the desired swirl ratio.
Swirl is the rotation of charge about the cylinder axis and it is used in diesel engines to control the mixing of fuel and air. Optimising the mixing of fuel and air minimizes pollutants.
Caepro has significant experience developing combustion chambers to meet certain performance and emission requirements.
Fig 1: Inlet port and valve assembly
Correlation of Port Flow Simulation to Paddle-Wheel Test Rig:
First, Caepro performed a steady-state CFD simulation of the baseline geometry in the paddle-wheel setup configuration.
The simulation predicted swirl ratio within 6% of the test rig. This gave the client confidence that further prediction based on recommended design changes would be replicated on the test rig.
Fig 2: Representation of Swirl Flow
Designing a Minimum Cost Solution:
Once the simulation had been correlated, Caepro focussed on designing a minimum cost design solution to meeting the target swirl ratio.
To achieve this Caepro investigated creating an offset chamfer on the cylinder flame face.
This required only a machining operation rather than expensive and time-consuming casting changes.
After a few iterations the target swirl ratio was achieved in simulation. When the modified head was place on the test rig the results were again within 6%.
With this confidence, the client built a complete engine to put on the engine test bed.
Fig 3: Without Chamfer Fig 4: After Inserting 5mm Offset Chamfer
Caepro was able to predict swirl ratio to within 6% of the paddle-wheel test giving the client confidence that our design changes would meet their requirements.
Caepro were able to meet the client’s swirl ratio targets by adding one machining operation to introduce an offset chamfer at the entrance of the inlet port to the cylinder.
This saved the client considerable cost and time by avoiding changes to the port itself which would have required changes to the casting.
The modified engine successfully met the emissions targets.
“Caepro’s ability to correlate their simulations so closely to the test rig gave us great confidence in their approach.The design modification proposed was a very practical, low-cost solution that enabled us to meet our objectives with minimum time and cost.” Head of Engineering, Engine OEM.
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