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These were used in an Ansys FE model to predict temperature distribution. For piston surfaces not directly sprayed the flat plate correlation was used taking mean piston speed for Re calculation.Īs such the thermal boundary conditions are: The calculated spray velocity was used to compute Re for use with a jet HTC correlation (Jigi and Dagn in this case).
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This might seem high but Cosworth have stated that the CA piston (42.4 m/s peak velocity) could outrun the spray at peak engine speed since the engine was running 1 bar lower oil pressure. The nozzle velocity obtained was 45.8 m/s.
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The cycle average temperature and HTC were used to define the boundary conditions in a thermal FEA.įor cooling, the piston spray velocity was calculated by solving Bernoulli across the nozzle (assuming 0 velocity within the oil gallery) for 8.5 bar oil pressure. The simulation used an unmodified Vibe curve for heat release and Annand's correlations for HTC prediction. The objective was to tweak the model in order to achieve a peak cylinder pressure of around 100 bar as this was the maximum suggested by Honda at peak torque during the V8/V10 eras.
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This was achieved by building a single cylinder model in a free version of Lotus Engine Simulation available online. Next on the list was to create an engine cycle simulation model to estimate the cylinder pressure, gas temperature and crown heat transfer coefficient. There is a slim chance I might be able to CMM it at work next year but for now it will have to do. To be able to analyze the piston I created a rough but hopefully representative CAD model. Again this is evident from the dark contact marks which are offset away from the edges. The piston pin runs straight into the aluminium bore.Įach pin bore half has edge relieves at both sides. These grooves break out into small axial relieves in the pin bore. The rod thrust faces have shallow angled grooves machined to provide lubrication. The piston skirt has an ample relief at the bottom - this is evident in the wear pattern since the xylan coating is almost untouched. The oil control ring groove contains 8 oil drain holes. Below the top ring there is a standard vee shaped accumulator groove. There are no gas slots - the gasses energizing the top ring have to travel through the clearance between the ring and the groove. The ribs blend nicely into the crown with approx. By contrast, the 98 mm diameter CA piston had straight pin bore ribs aligned with the T ribs. This sometimes has the disadvantage of reducing the ring belt support, particularly for larger bore pistons. The pin bore ribs are slightly angled, presumably to direct the load towards the T rib. As the TJ did not have compound valve angles the crown dome is fairly clean.Īn interesting feature is the small pocket on the under crown that matches the intake squish land. The exhaust valve pockets break out into the top land, while the intake pockets are fully contained within the crown and form a thin wall at the closest point to the top land. DLC coatings were experimented with but the processes for applying DLC to aluminium were still in their infancy at the time and usually resulted in poor substrate adhesion or reduction in strength due to the high temperatures required. The skirts are Xyalan (1000s series) coated. The undercrown is shot peened and polished while the crown is simply just polished.
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The piston is of a fairly standard box bridged construction and made of A2618 which has been used in Cosworth pistons since the DFV. Towards the end of its development it reached 19,000 RPM and a peak power of about 920 hp. The TJ was Cosworth's last F1 V10 having been introduced in 2003 and replaced in 2006 by the CA V8. I thought it would be an interesting exercise to attempt to calculate the piston thermal and mechanical loads based on the information available on these engines. Earlier this year I've acquired an used TJ piston as well as a rod courtesy of BrianG.