Heavy-Duty Diesel Engine Cooling SystemsTom McKinleyCummins, Inc.

ObjectivesProvide background information useful to tomorrows lab project (Evaluation of a Water Cooled Exhaust Manifold). Topics covered:Typical heavy-duty (HD) diesel engine designsCommon HD automotive diesel applicationsIntroduction to engine cooling systemsArrangementDevelopment ToolsDesign Constraints

Typical HD Diesel Engine Design10 to 15 liters displacementInline-sixTurbochargedAir-to-Air Aftercooling300-600 hp at 1600-2100 rpm1250-2000 lb-ft Max Torque at 1200 rpmDry weight 2000-2800 lbReliability/Durability250,000 mile/2 year base warranty500,000 mile/5 year extended warranty1,000,000 mile life expectation

Typical HD Diesel Engine Application80,0000 lb GVW100,000 to 150,000 miles per year6 MPGOperating range from sea level to >8,000 ft altitudeAmbient temperatures from below zero to 115 deg F

Typical HD Diesel Engine Duty CycleAverage load of 180-200 hpMost of fuel used at cruise rpm of 1400-1700 rpmVarying load at cruise due to operation of cruise controlVarying engine speed due to road speed changes in traffic or urban operation

Thermo-Fluid Systems on HD Diesel EnginesCooling SystemAir Handling SystemLube SystemFuel System

Qhead+QblockEngine Cooling System LayoutQoilQmnfQradWpump

Functions of the Cooling SystemTo prevent excessively high and low engine component temperaturesTo provide a heat sink for the lube systemTo reject engine heat to the ambientTo provide a heat source for the truck cabTo provide a coolant source for other OEM equipment (e.g. torque converter coolers, fuel heaters)The optimal cooling system meets system requirements whileminimizing life cycle cost (initial cost, warranty/reliability,operating/fuel cost). Tomorrows lab will give you the opportunityto evaluate designs from a life cycle cost perspective.

Design Control ResponsibilitiesWater PumpOil CoolerLinersHeadsWater Manifold/Water HeaderThermostatBypassRadiatorCharge Air CoolerFreon CondenserRadiator FanFan Drive (Drive Ratio, Fan Clutch)Fan ShroudAir DamsCab HeaterAuxiliary CoolersEngine ManufacturerTruck Manufacturer

Cooling System Development TechniquesWater Pump Performance TestingEngine Flow StandFlow BenchFlow Circuit SimulationCFD AnalysisFE AnalysisThermal Mapping TestOil Cooler Performance TestingChassis Dyno

Cooling System Constraints

Water Pump Performance TestUsed to determine:Pump capacity (flow rate) as a function of pressure rise and pump speed

Pump efficiency and parasitic power

NPSH and cavitation temperature

Water Pump CavitationWhat is It?The formation of vapor at the pump inlet due to local pressures dropping below the saturation pressure.When does it Occur?High coolant temperatures (high saturation pressure)High coolant flow rate (low local static pressure)Why is it Important?Leads to a reduction of pump flow rate, therefore lower radiator effectiveness, therefore higher coolant temps, therefore more cavitation (runaway coolant temperatures)Leads to an increase in water pump seal temperature (fails the seal)Theoretically can lead to erosion of the impeller but generally the failure modes listed above occur first.

Typical Water Pump Map

Engine Flow StandUsed to determine:Radiator flow rate vs radiator restrictionCoolant pressure distribution within engineCoolant flow rate through external components

Allows estimation of coolant flow distribution within engine using flow circuit modeling

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Engine Restriction Curve Overlayon Pump MapDP is proportional to the square of the flow rate (energy equation -> DP is proportional to V squared)

Pump head rise is proportional to the square of the pump speed

Flow rate is linear with engine speed

Flow BenchUsed to determine:Component coolant flow vs pressure drop relationship (hydraulic resistance)

On-engine component coolant flow rates and parasitic power using flow circuit simulation or flow stand testing

Hydraulic Resistance:Analogy to Electrical CircuitsGeometric ElementsResistive ElementsBoth equations are of the form:Note that voltage (v) is analogous to pressure drop,and current (i) is analogous to volumetric flow rate.

Hydraulic resistance is a function of the flow rate. Because ofthis non-linearity, iteration is needed to obtain hydraulic circuitsolutions.

Flow Circuit SimulationBased on the analogy of hydraulic and electrical circuits

Used to determine:Cooling system parasitic power by component and for the entire systemCoolant flow distribution within the engineApproximate coolant velocity

Assists the design effort by allowing the design to be iterated quickly before hardware is procured.

CFD AnalysisUsed to determineCoolant pressure drop for use in flow circuit modelingVelocity distributionCoolant side boundary conditions (temperature and heat transfer coefficient) for thermal FE analysisModel predictions are validated by thermal mapping, flow bench testing, and flow visualization.

FE AnalysisUsed to determineComponent temperaturesComponent stressesFatigue life

Model calibrated to thermal mapping engine measurements

Thermal Mapping TestUsed to calibrate thermal FE models

Oil Cooler Performance TestUsed to determine:Oil cooler heat transfer rate as a function of oil flow, coolant flow, and fluid temperatures

Oil cooler coolant and oil side restriction

On-engine oil cooler coolant flow rates and parasitic power using flow circuit simulation or on-engine testing

Truck Cooling Package LayoutNote: Tomorrows lab includes optimization of a truck cooling package

Chassis Dyno FacilityUsed to determine coolant temperatures and engine heat rejection under simulated hot ambient conditionsCapable of handling the largest HD trucks and engines5 foot by 7 foot air tunnel can provide up to 35 MPH ram air into radiatorMixing ambient air with recirculated air allows the air temperature into the radiator to be varied to limiting ambient conditions (100-115 deg F)

Chassis Dyno Schematic

SummaryCooling system design requires the optimization of components and the system as whole to meet competing objectives of:Initial CostWarranty/reliabilityOperating/fuel costCooling system components are under the design control of both the engine and truck manufacturer. Cooperation is needed to deliver the best product to the end user.