To provide sufficient cooling to the engine to let it operate at peak power throughout an endurance event, at the targeted 10,000 to 14,000 rpm operating range, under competition conditions.
A single-pass water-to-air heat exchanger takes heat out of the coolant. A Pierburg CWA100-3 electric pump at the lowest point in the system moves roughly 40-50 L/min of coolant through the engine and back through the radiator on AN-16 BMRS lines with crimped fittings. A swirl pot with a radiator cap sits at the highest point in the system; its angled tangential inlet uses centrifugal force to separate air and vapour from the coolant, and the cap makes it the pressure reference and the bleed point. A coolant catch can takes the overflow. A 9 in Spal fan on a carbon fiber shroud pulls air through the core when the vehicle is not moving fast enough to do it, activated automatically at 96 C water inlet temperature. A separate oil-to-air heat exchanger handles the lubrication system, fed through a Setrab sandwich plate adapter at the OEM oil cooler location, with its own 5.2 in Spal fan activating at 90 C oil temperature.
Design so the car can be sufficiently cooled solely when stationary. That is the worst case, it removes the dependence on vehicle speed, and it is what makes the endurance event survivable in traffic. Size from measured heat rejection, not from a rule of thumb. The MATLAB NTU-epsilon sweep starts from heat rejections measured on the previous year's endurance and sweeps core length, width, thickness, fin density, water mass flow and air mass flow until the candidate rejects significantly more than the maximum seen. CR25's mock half endurance measured average heat rejection of 23.7 hp and a maximum of 32 hp; CR26I's radiator is sized to dissipate 35.26 hp. 1. Define measured heat rejection from previous-year endurance data. 2. Iterate core parameters in the MATLAB NTU-epsilon analysis until the target is beaten with margin, at the stated assumptions: steady state, single-phase water, constant air mass flow from CFD at 32 mph average endurance speed, 105 C water inlet, 27 C air inlet, constant fluid properties. 3. Give the core geometry to Aerodynamics for duct, shroud and radiator angle design; take back the achieved mass airflow. 4. Lay out the water loop: pump at the lowest point, swirl pot cap at the highest, bleed valve on the top tank, temperature bungs at inlet and outlet. 5. Validate on a mock endurance with inlet and outlet thermistors and back-calculate heat rejection.
- Adequately cool the engine while operating in the 10,000-14,000 rpm target band under competition conditions. - Incorporate the aerodynamic analysis into component sizing and cut system mass. CR26I cooling total 15.2 lb against CR22's 28.2 lb, a 13 lb / 55.5% reduction. - Reduce weight everywhere: radiators 10.8 to 7.25 lb, fans and shroud 3.75 to 1.33 lb, lines 5.66 to 1.5 lb, fittings 2.58 to 1.68 lb. - Keep combined fan current draw under the 15 A allowance. CR26I sits at 12.6 A combined. - Gain in-depth understanding backed by data and testing. - Improve Aerodynamics and Powertrain integration to remove the need for a cooling fan entirely.
- Air stuck in the cooling system. Solved by removing the thermostat and then bleeding the system. This is also the CWA100 pump's recurring complaint: air gets trapped in the pump. - The duct being blown off the radiator by pressure. Solved with stronger metal fastening and by attaching the sidepod to hold the duct in place. - The radiator not using its full surface area to cool. No solution yet. - EWP80 coolant pump leaking. Pumps were swapped regularly, then the team moved to the CWA-series pump. - Peak water temperature reaching 113.5 C on a mock half endurance against a 115 C maximum and a 126 C boiling point at system pressure. The margin is real but thin.
MATLAB NTU-epsilon heat exchanger sizing (referenced to Bergman, Fundamentals of Heat and Mass Transfer, 8th ed.). ANSYS Fluent porous media simulation with Darcy-Forchheimer coefficients from flow bench testing, and a fan boundary condition from the manufacturer curve. Flow bench for radiator and oil cooler pressure-drop curves. MoTeC i2 Pro for on-track inlet/outlet temperature and back-calculated heat rejection. GT Suite for future full-system analysis.