Ic engine most important mcq questions with answers most important mechanical engineering mcq on ic engine. Knocking should not be confused with preignitionthey are two separate events. Spark knock is a pinging noise, rattling or knocking which might be heard while the engine is working hard under load passing on the highway, towing a trailer, driving up a mountain, etc. These det cans can be either electronic or mechanical, the former using a microphone to transmit the audio through a pair of headphones, and the latter just using a copper mount and tubing to transmit the sound picked up by the copper to the headphones. The air motion so organized inside the combustion chamber and the turbulence of the air passes across the fuel jet tears it into fine particles. Study of knocking effect in compression ignition engine. In addition, detonation could be initiated near the walls in ic engines if the energy density is high enough. Because of the noise that it makes, detonation is called engine knock or pinging in cars. Knocking and detonation is physically same like nosiy sound. Under normal conditions, the combusting air and fuel mixture inside the combustion chamber ignites in a controlled manner. Preignition is an uncontrolled combustion event which occurs before the spark event. Some engines, such as liquid cooled 2stroke engines found in snowmobiles, watercraft and motorcycles, have a very common detonation failure mode.
It is caused due to the propagation of a high speed pressure wave created by the autoignition of end portion of unburnt fuel. Marshall engineers and industry partners united technology research corp. Knock control benefits vehicle engines work more efficiently and produce more power when operating near. Prolonged and intense knocking can break the piston or the engine, though it is can also endure this slight issue for thousands of miles. The effect of strokebore ratio on engine friction and economy is very small. Knocking is generally not heard at high speed and power settings because of the noise developed in air intake or exhaust system is louder and masks. What is the meaning of knocking and detonation in i. This is achieved by using small engines having larger rpm and larger engines having smaller rpm. Effect of knocking in spark ignition in a fourstroke engine authors ravikant sahu1, eklabya gupta2.
So, we have understood that in a spark ignition engine combustion is initiated, you know. Mild detonation may increase engine wear, though some engines can operate with mild detonation regularly. Knocking and detonation refer to the same phenomena in internal combustion engines. The compression ratio is very important in many aspects of both compression and spark ignition engines, by defining the efficiency of engines. This video explains knocking combustion and preignition and the reasons for this irregular combustion. Internal combustion engines can be classified internal combustion engines ca n be classified n be classified as c as cas continuous ic engines and ontinuous ic engines and. Us2220558a detonation suppression system for internal. Ill add a couple of thoughts that come to mind when i think about knocking and detonation. Unintentional detonation when deflagration is desired is a problem in some devices. What typically happens is that when detonation occurs the piston expands excessively, scurfs in the bore along those four spots and wipes material into the.
Knocking combustion in sparkignition engines article pdf available in progress in energy and combustion science 61. The airfuel charge is meant to be ignited by the spark plug only, and at a specified time during the normal cycle of the piston. What is the difference between knocking and detonation. Knocking also knock, detonation, spark knock, pinging or pinking in sparkignition internal combustion engines occurs when combustion of some of the airfuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of airfuel mixture explode outside the envelope of the normal. Knocking in spark ignition internal combustion engines occurs when combustion of some of the. Most oem knock sensors are basically microphones tuned to listen for a specific. It the temperature of intake air in ic engines is lowered, then its efficiency will a increase b decrease. The piston is bourn due to high temperature of the unbrount charge in knocking.
Effect of engine operating variables on the engine knocking detonation. The resulting knock or ping is the sound of the pistons slamming against the cylinder walls. Knocking is the noise you hear caused by detonation,which is an explosion or uncontrolled burning inside the cylinder of a reciprocating engine. Engines the loud pulsating noise heard within the engine cylinder of an i. A knocking sound is the most typical engine noise indicating a mechanical problem that can be fixed if diagnosed correctly and early. Noted below are a few facts about why an engine knocks and what can be done to resolve these issues. Knocking or also called detonation in ic engines, in ignition spark engine, occurs when the incorrect ignition of the air fuel mixture in the some cylinder occurs while other cylinders correctly combust and produce the power stroke at the correct time. Similarly, overheating may cause additional wearandtear on the engine, be relatively harmless or cause the engine to catch on fire and break. Pressure waves accompanying detonation in the internal. Internal combustion ic engine study notes handwritten. Internal combustion enginel is a fair summary of the opinions existing at the present time. There are different types of ic engines that can be classified on the following basis.
Interaction of flame propagation and pressure waves during knocking combustion in sparkignition engines 21 january 2014 combustion science and technology, vol. Knocking combustion causes major engine damage, and also reduces the efficiency. In internal combustion engines it is called engine knocking or pinging or pinking, and it causes a loss of power, excessive heating, and eventual engine failure in some cases. Knocking and detonation are not what you want occurring in your engine 2.
However, severe detonation can cause engine failure in minutes. Phenomenon of knock in ci engine is called knocking and phenomenon of knock in petrol engine is called detonation. In the flames of internal combustion engine there is con stant thermal. What is the difference between knocking and detonation in ic engine. As the flame propagates across combustion chamber, end gas is compressed causing pressure, temperature and density to increase. Knocking, in an internalcombustion engine, sharp sounds caused by premature combustion of part of the compressed airfuel mixture in the cylinder. The usage of hydrogen in compression ignition engine leads to production of knocking or detonation because of its lower ignition energy, wider flammability range, and shorter quenching distance. Knocking combustion in sparkignition engines sciencedirect.
Knocking in your engine, also described as pinging, can mean one of several problems. And ci engines in sparkignition engines, the autoignition of. What is the difference between knocking and detonation in. Detonation or knocking in ic engines mechanical engineering. Professional tuners often rely on the use of detonation cans det cans to detect knock events on highly modified engines. Knocking or detonation or pre ignition what is knocking detonation pre ignition. Knock pinging is the actual noise that can be audibly heard if detonation is bad enough.
Detonation is an uncontrolled combustion event which occurs after the spark event. Detonation occurs when the pressure and temperature inside the cylinder become higher than the critical pressure and temperature of the fuel. Detonation and knocking 80 theories of detonation 82 effect of engine variables on knock 83. The high velocity knock, usually called detonation,will produce severe damage of the engine and is avoided by the electronic engine control. Detonation is when the fuel explodes rather than burning. High strokebore ratio engines have equally good friction mep values as that for low strokebore ratio engine.
Due to same piston speed, the inlet velocity, degree of turbulence and flame speed are nearly. This autoignitioninduced flow pushes back the sparkignited flame front and creates a further negative curvature. Theory of detonation in turn assumes initiation of knocking as a result of flame front. Powerpoint slide on knocking in ic engines compiled by raja hossain.
Engines objective questions and answers pdf,interview questions,multiple choice questions,lab viva,seminar topics,online quiz important free download. In a properly functioning engine, the charge burns with the flame front progressing smoothly from the point of ignition across the combustion chamber. The violence of detonation also causes a reduction in power. Composition factor the detonation or knocking in ci engine can be reduced by using certain fuel additives which would increase the cetane number of the fuel. Knocking occurs when parts of the supplied fuelair mixture do not explode at the optimum point in the combustion process of a 4 stroke cycle. The effects of detonation may be anywhere from arbitrary to severe. Mild detonation is called knocking because of the noise that can be heard when it happens at low power settings. But for ci engines higher the compression ratio, lesser is the ignition delay and lesser probability of detonation or diesel knock occurring. The noise which gives the name of knocking to detonation is like. It was found that detonation can occur in modern internal combustion engines under high energy density conditions. Thus, a 2nd autoignition occurs with much more pressure rise intensity near walls. Knocking is violet gas vibration and audible sound produced by extreme pressure differentials leading to the very rapid rise during the early part of uncontrolled second phase of combustion. The application of ethanol in engines with a high compression ratio is favoured because of its high knock resistance, due to a higher octane number 31, and high heat of evaporation 32 in comparison with gasoline, reducing the temperature of the mixture and resulting in increased engine power and efficiency 15,33. Effect of knocking in spark ignition in a fourstroke engine.
The effect of knocking in piston and piston cylinder is crack and defect in piston head as shown in fig. The mixture is ignited by the spark, normally in the centre of the cylinder, and a flame front moves from the spark towards the outside of the cylinder in a controlled burn. Detonation, as is known, is a phenomenon occurring in internal combustion engines improperly adjusted or under severe conditions of operation. The two chemical drops normally used are, ethyl nitrate 33gmsus gallon 29gmsus gallon amyl nitrate higher the. Keep your vehicle running smoothly quality governing of internal combustion engine in this video, i explained quality governing of internal combustion engine. What is the difference between knocking and detonation in internal. Engines of similar design generally run at the same piston speed. Knocking also called knock, detonation or spark knock, pinking in uk english or pinging in us english in sparkignition internal combustion engines occurs when combustion of the airfuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of airfuel mixture explode outside the envelope of the normal combustion front. Pdf knocking combustion in sparkignition engines researchgate.