OHIO TECHNICAL COLLEGE June 27th, 2018 Cleveland, OH Sean Bennett Cengage Learning

Diesel Combustion and Emissions A primer in cylinder combustion dynamics and how end gases are produced modern diesel engines

Fundamentals of in-cylinder combustion – keeping it simple What is air? What is fuel? Physics of engine torque production Chemistry of combustion End gas combustion

Diesel Cycle Review

Intake Turboboosted air forced into cylinder Excess air: depends on mode of operation – varies between as much as 600% at idle to as little as just over stoichiometric at peak torque (λ< 1) Air is a mixture of N2 (78%) and O2 (21%) EGR is also introduced into the cylinder EGR cut percentage varies by manufacturer and mode of operation

EGR Exhaust discharge is the most convenient source of ‘dead’ (unreactive) gas It dilutes the intake charge (of oxygen) and lowers combustion temperatures It can be cooled and may be ‘cleaned’ (Cat CGI) sourced downstream DPF EGR cut-percentage is ECM controlled

Compression and Power Strokes

Lean Burn Technology Emissions tightrope: combustions temperatures must be managed High temps (lean burn): ++ NOx Low temps: ++ HC (incl PM) 1988 to 1997: ECM managed After 1997: phased intro of emissions hardware

ASTM ULS Diesel Fuel Petrochemical HC: + 85%C + 14% H Max Sulfur: 15 ppm (0.0015%) CN rating: defines ignition temp #2D: (min CN 40) summer cut + 45 Ignition temp CN 40: + 5500 F (2900 C)

High injection pressure driven through a fixed orifice = smaller fuel droplets

Diesel Fuel Injection Pressure Diesel fuel is pumped through a fixed flow area defined by the injector orifice size Pressure at the injector orifice(s) (rail pressure) determines fuel droplet size Optimum droplet size: 10 – 15µ (microns)

Crank Leverage Geometry

Hydromechanical era: hard values – combustion events dependant on pump port closure

HD Diesel CR System Layout

Electrohydraulic Injector (EHI)

Paccar Delphi CR System

CR Injection Control and Combustion

Multipulse Diesel Fuel Injection Controls injection rate to manage cylinder pressures during power stroke Managing cylinder pressure = smooth mechanical transition of torque to the engine powertrain (crankshaft) Optimizes combustion of fuel to minimize end gas pollutants

Diesel Exhaust Process End gases must be removed from cylinder Begins when exhaust valves open: occurs before BDC on the power stroke

Exhaust Purge Events Pressure differential: gas blowdown during piston downstroke Inertial purge: piston at BTDC Displacement: piston moves to TDC Scavenging: Exhaust valves closing, intake valves opening. Maybe extended in diesel engines.

Valve Operation

End gas composition CO2 (a pollutant since 2007 Supreme Court ruling) H20 (a GHG when produced in a redox reaction) Other: NOx PM Uncombusted gaseous HC Uncombusted liquid HC

DOC Diesel oxidation catalyst Uses platinum and palladium catalysts Used for a generation in diesel engines and is located upstream from DPF Reaction temps range from 8000 -10000 C

DPF A soot trap for emission solids known as particulate matter (PM) PM is entrapped by filters and collected When soot reaches a threshold value, the DPF must be regenerated Regen reduces soot to unreactive ash

DPF Entrapment Principle

DPF regeneration modes Passive: set to occur when soot build-up has reached a threshold and engine exhaust temps are high enough Engine is usually under load and the vehicle is running at highway speeds Exhaust gas heat (600 C plus) is used to burn-off soot to unreactive ash Ash is then collected

DPF regeneration modes Active: occurs when DPF soot levels exceed a threshold value ECM-controlled when vehicle operating conditions permit ECM-diagnostic software generated May require: fuel to be injected into the exhaust gas and spark-assist ignition

SCR NOx reduction agent used in gasoline fueled engines (rhodium) only functions as a catalyst when stoichiometry is <15:1 SCR uses ECM-managed DEF (aqueous urea) injection to reduce NOx compounds back to elemental O2 and N2 DEF is a consumable that must be replenished: levels are ECM-monitored and are EPA-required to progressively cripple the engine if refill alerts are ignored

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