Engine Performance Parameters and Emission Control Technologies

Vocabulary practice flashcards covering internal combustion engine design parameters, cylinder geometry, valve actuation, PCV systems, EVAP canisters, EGR mechanisms, and catalytic exhaust aftertreatment technologies.

Engine Cylinder Geometry

The structural configuration of an internal combustion cylinder where poppet valves, a fuel injector, and the piston govern fluid flow and combustion, translating linear motion between top-dead-center (TDC) and bottom-dead-center (BDC) into rotational crankshaft motion across crank-angle degree $\theta$.

Engine Performance

An indication of the degree of success with which an internal combustion engine accomplishes its assigned task of converting the chemical energy contained within the fuel into useful mechanical work.

Compression Ratio (CR)

The ratio of the cylinder volume and its head space when the piston is at the bottom of its stroke (BDC) to the volume of the head space when the piston reaches top dead center (TDC). Typically, petrol engines operate with a CR of $8\text{ to }10$, while diesel engines operate with a CR of $15\text{ to }20$.

Engine Knocking

An abnormal combustion phenomenon occurring in spark-ignition engines when fuel-air mixture autoignites thermally prior to spark initiation, rather than burning uniformly across the combustion chamber.

Octane Number

A standard rating of petrol quality that dictates the compression ratio at which thermal pre-ignition occurs, where higher values permit operation at higher compression ratios without knock.

Hemispherical Combustion Chamber

A combustion chamber design characterized by an inclined two-valve configuration that provides the lowest surface-to-volume ratio, high air swirl, and minimal knocking tendency.

Pentroof Combustion Chamber

A shallow-angle combustion chamber design accommodating four valves per cylinder that generates tumble air motion and higher burning rates while minimizing quench layer thickness to lower $\text{HC}$ emissions.

Port Fuel Injection (PFI)

An electronic fuel delivery system utilizing an individual injector per cylinder positioned at each intake port, eliminating the carburetor venturi restriction and improving volumetric efficiency and mixture distribution.

Gasoline Direct Injection (GDI)

A fuel introduction system that delivers gasoline directly into the engine cylinder, enabling downsizing and improved fuel economy, but with an increased tendency to generate small particulate matter emissions.

Valve Overlap

The interval during engine cycle events when both intake and exhaust valves remain simultaneously open; large overlap utilizes the ram effect for high volumetric efficiency at high speeds, whereas low overlap avoids residual gas backflow at low speeds.

Variable Valve Lift

A valve actuation feature that adjusts valve lift depth based on engine load and operating speed, maintaining high intake charge velocity and turbulence at low loads for stable combustion.

Multiple Valves Configuration

The arrangement of four valves (two intake and two exhaust) per cylinder in spark-ignition engines, allowing central spark plug placement, reduced flame travel distance, decreased knock propensity, and increased total flow area.

Positive Crankcase Ventilation (PCV) System

An add-on engine emission system that uses intake manifold vacuum to draw harmful blow-by gases and fuel vapors out of the crankcase and into the intake manifold for combustion.

Open PCV System

An early crankcase ventilation setup that pulls fresh air via a vented oil filler cap, but discharges excess contaminated vapors into the atmosphere under high crankcase vapor volumes.

Closed PCV System

A crankcase ventilation design standardized after $1968$ that supplies fresh air from the air filter housing and utilizes a sealed, non-vented oil cap to prevent blow-by vapors from escaping into the open atmosphere.

PCV Valve Operation

A vacuum-actuated metering valve containing a spring-loaded plunger that moves fully forward under high manifold vacuum at idle to restrict flow, and opens wider under lower vacuum during cruise or acceleration.

Evaporative Emission Control (EVAP) System

A sealed fuel vapor management system that traps hydrocarbon vapors emitted from the fuel tank and lines to prevent photochemical smog formation, eliminating up to $20\%$ of vehicle pollution.

Liquid-Vapor Separator

A device positioned above the fuel tank or within the overflow tank that uses a float-and-needle assembly or foam dome to block liquid petrol from entering and overloading the EVAP canister vent line.

EVAP Canister Operation

The process in which activated carbon inside a storage canister adsorbs and holds fuel tank vapors until the powertrain control module commands a purge solenoid open, allowing intake manifold vacuum to siphon stored vapors into the engine cylinders.

Exhaust Gas Recirculation (EGR) System

An emission control configuration that diverts a measured portion of inert exhaust gases back into the cylinder charge, reducing oxygen concentration and lowering peak combustion temperatures to inhibit $\text{NO}_x$ formation.

Thermal Reactor System

An exhaust treatment arrangement consisting of two enlarged exhaust manifolds and a secondary air pump that injects fresh air into hot exhaust gases, providing sufficient residence time to oxidize unburned $\text{HC}$ and $\text{CO}$ into $\text{CO}_2$.

Diesel Particulate Filter (DPF)

An exhaust aftertreatment component installed in diesel exhaust streams that physically traps particulate matter and soot, achieving emission reduction efficiencies of over $90\%$.

Selective Catalytic Reduction (Urea-SCR)

A catalytic aftertreatment system that injects an aqueous urea solution into the diesel exhaust stream to reduce $\text{NO}_x$ emissions into harmless nitrogen and water with over $90\%$ efficiency.

Three-Way Catalyst (TWC)

The primary emissions aftertreatment catalyst used on stoichiometric spark-ignition engines to simultaneously eliminate over $90\%$ of $\text{NO}_x$, $\text{HC}$, and $\text{CO}$ emissions.

Diesel Oxidation Catalyst (DOC)

A diesel exhaust aftertreatment catalyst that promotes rapid oxidation of $\text{HC}$ and $\text{CO}$, while oxidizing $\text{NO}$ to $\text{NO}_2$ to enhance the downstream function of SCR and DPF systems.