Engine Technology Induction System Combustion in Engine 1

Engine Technology Induction System Combustion in Engine • 1. 2. • fuels (gasoline) are made up mostly of two elements. hydrogen (H) carbon (C). Hydrogen and carbon can be joined to create various hydrocarbon (HC) fuels • Oxygen forms about 21 percent of our atmosphere. Hydrogen and carbon unite with a third element, oxygen (O) to produce the complete combustion. • 1. 2. 2. 3. • During complete combustion: Each oxygen atom unites with two hydrogen atoms – Oxygen uniting with hydrogen produces H 2 O (water). Each carbon atom unites with two oxygen atoms – Carbon uniting with oxygen produces CO 2 (carbon dioxide) All the hydrogen & carbon (HC) in the gasoline would unite with oxygen and exhaust gas would contain only harmless H 2 O (water) & CO 2 (carbon dioxide).

Engine Technology Induction System Combustion in Engine • If combustion in the engine is not perfect: 1. 2. 3. Some of the gasoline (HC) does not burn. Also, some only partly bums – carbon monoxide (CO). (Monoxide because only one oxygen atom for each carbon atom. ) • It will exit from the engine through the tailpipe and cause atmospheric pollution. • Another group of atmospheric pollutants from engine is nitrogen oxides (78% of the atmosphere is the gas nitrogen). The high temperatures in the engine cause some of the nitrogen to unite with oxygen. This forms the nitrogen oxides. •

Engine Technology Induction System Gasoline Characteristic • made from crude oil (petroleum) that was refined and several additives are put into gasoline to improve its characteristics for use as an engine fuel. • specified gasoline for an automotive engine should have 1. 2. 3. 4. 5. 6. 7. Proper volatility – determines how easily the gasoline vaporizes (turns to vapor). Resistance to spark knock or detonation. Oxidation inhibitors, which prevent formation of gum in [the fuel system. Antirust agents, which prevent rusting of metal parts in the fuel system. Anti-icers, which retard icing in the throttle body and fuel-line freezing. Detergents, which help keep the carburetor or fuel injectors clean. Dye for identification - red dye for leaded gasoline Volatility • determines how quickly a gasoline vaporizes. - A high volatility gasoline vaporizes quickly (Vapor lock results if volatility is too high) - A low volatility gasoline vaporizes slowly (if volatility is too low. Not enough fuel vaporizes to produce a combustible mixture)

Engine Technology Induction System • 1. 2. 2. 3. 4. 5. gasoline must vaporize quickly after it’s mixed with air in the intake manifold. Otherwise, drops of gasoline enter the cylinders and wash oil off the cylinder walls. This increase wears of the cylinder walls, pistons, and rings. non vaporize gasoline will not burn and leaves the cylinder with the exhaust gas. Catalytic converter removes most of the HC from the exhaust gas. Th rest goes out the tailpipe and pollutes the air. 3. This wastes gasoline and reduces fuel economy Antiknock Quality • How well gasoline resists spark knock or detonation, determines whether normal combustion or abnormal combustion occurs. • Spark knock or detonation can seriously damage an engine. The heavy shocks on the pistons put great load on bearings and other engine parts

Engine Technology Induction System Octane Ratings • antiknock quality of gasoline is indicated by its octane number. The higher the octane number, the more resistant of gasoline to produce spark knock • 93 octane gasoline (premium) is more knock resistant than an 87 octane gasoline (regular) – gasoline that knocks or detonates easily is a low octane gasoline and gasoline that resists detonation is high octane gasoline. • Before 1975 – tetraethyllead (TEL) is added to the gasoline because lead allowed higher compression ratios without detonation. After 1975 – Federal regulations have required that all new cars run on unleaded fuel. Lead added to gasoline does not bum & leaves with the exhaust gas and pollutes the air.

Engine Technology Induction System Octane Requirement • engine design and compression ratio determine the octane it requires. However, this requirement changes with weather: 1. 2. 2. 3. 4. 5. Driving conditions - octane requirement will be lower if the driver does not demand rapid acceleration and high-speed wide-open-throttle operation Mechanical condition of the engine – combustion chamber deposits reduce clearance volume. They also increase octane requirements and the possibi of detonation. Reduced cooling efficiency, fuel system or ignition troubles, and failure of emission controls may also change octane requirements Other Types of Abnormal Combustion • called surface ignition and can occur before or after the spark where mixture starts to bum, or pre ignites from hot spots in the combustion chamber • 1. 2. 3. 4. Possible causes: hot chamber surface – exhaust valve, piston head wrong spark plug carbon deposits – hot carbon deposits ignite the fuel before spark occurs wrong fuel

Engine Technology Induction System • shape of the combustion chamber has an effect on detonation. 1. 2. 3. 4. 5. Wedge chamber – flame front must travel across the chamber. The end of the wedge has a squish and quenches area. This helps prevent detonation of the last part of the unburned air-fuel mixture or end gas. The squish occ at the end of the compression stroke. The mixture is squeezed out (squishe so fast so it promotes turbulence. The turbulence improves combustion 2. 3. 4. Hemispheric combustion chamber – has a centrally located spark plug. The flame front travels only a relatively short distance. There are no distant pockets of end gas that could detonate

Engine Technology Induction System Detonation • Also called "spark knock" and it’s occurs when excessive heat and pressure in the combustion chamber cause the air fuel mixture to autoignite. • This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise • Mild or occasional detonation can occur in almost any engine and usually causes no harm. But prolonged or heavy detonation can be very damaging. So if you hear knocking or pinging when accelerating or lugging your engine, you probably have a detonation problem. • Factor that contributing detonation: 1. Wrong fuel usage – lower octane rating or higher octane rating. 2. High compression ratio – compression ratio of 9: 1 normally recommended limit for most naturally aspirated street engines.

Engine Technology Induction System Detonation 3. Wrong adjustment of ignition timing – too advance 4. Defective of knock sensor 5. Air fuel mixture – rich fuel mixtures resist detonation 6. Boost pressure – controlling amount of boost in turbocharged engine 7. Carbon deposit in combustion chamber 8. Engine working temperature 9. Heated intake air system 10. Spark plug range - wrong heat range plug can cause detonation 11. Driving habits - Instead of lugging the engine, try downshifting to a lower gear or accelerating more gradually.

Engine Technology Induction System Preignition • Occurs when a point within the combustion chamber becomes so hot and it becomes a source of ignition that ignite the fuel before the spark plug fires • fuel that ignites prematurely (early) causing a momentarily backlash as the piston tries to turn the crank in the wrong direction. • Preignition can also make itself known when a hot engine is shut off. The engine may continue to run even though the ignition has been turned off because the combustion chamber is hot enough for spontaneous ignition • Causes of preignition: 1. Carbon deposits form a heat barrier 2. Overheated spark plug (too hot a heat range for the application). 3. Glowing carbon deposits on a hot exhaust valve (valve is running too hot because of poor seating, weak valve spring).

Engine Technology Induction System Preignition 4. A sharp edge in the combustion chamber or on top of a piston (rounding sharp edges with a grinder can eliminate this cause). 5. Sharp edges on valves that were reground improperly (not enough margin left on the edges). 6. A lean fuel mixture. 7. Low coolant level, slipping fan clutch, inoperative electric cooling fan or other cooling system problem that causes the engine to run hotter than normal