Factors affecting knocking in si engines pdf merge

Study of knocking effect in compression ignition engine. Performance of an automobile engine is based on the various factors that affect combustion in engines. Engines mechanical engineering multiple choice questions and answers list. This is not acceptable and causes harm to the engine.

High mean pressures produce increased knocking, which frequently results in a reduction in the compression ratio at high specific powers. When fuel is improperly ignited, it causes a fireballlike explosion that can interfere with the engine s cycles and can even damage engine components these premature detonations are the source of the ping noise. The effects of detonation may be anywhere from arbitrary to severe. The most important factors which affect the flame speed are. Higher intake air temperatures increase the occurrence of engine knock. Factors determing ignition and efficient combustion in modern. As large engines operate at low revolutions per minute rpm because of inertia stress limitations, the delay period in terms of crank angle is smaller and hence less fuel enters the cylinder during the period. This video explains knocking combustion and preignition and the reasons for this irregular combustion. Hydrogen is one of two natural elements that combine to make water. The highpressure and hightemperature of the compression stroke combine with the internal heat to. Engines mechanical engineering multiple choice questions and answers list sunday, 31 august 2014 250 top i. From your past experience and training, you know that engine efficiency and performance depend upon much more than just operating the throttle and changing oil at prescribed intervals. Factors determining antiknocking properties of gaseous fuels in spark ignition.

A knocking sound is the most typical engine noise indicating a mechanical problem that can be fixed if diagnosed correctly and early. A sdvosb service disabled veteran owned small business. The same reason also affects the power output which is observable at the time of acceleration. The factors which affect the flame propagations are 1. Spark ignition engine an overview sciencedirect topics. The factors which affect the flame propagations are the factors wh ich affect the flame propagations are ich affect the flame propagations are 111. Fuel consumption of engine increases drastically as heat energy is lost during knocking. Particularly for spark ignition engines a high octane number of fuel is needed for. Higher combustion efficiency and fuel economy can be achieved by higher flame propagation velocities. Knocking in your engine, also described as pinging, can mean one of several problems. In this article, i am going to explain the various factors which will affect the combustion process. What are the various factors that affect the flame speed.

Pdf knocking combustion in sparkignition engines researchgate. Similarly, overheating may cause additional wearandtear on the engine, be relatively harmless or cause the engine to catch on fire and break. Engines aice important part b 16 marks questions, pdf books, question bank with answers key, me6016. Certain chemical changes must first occur for knock to happen. Describe a 3 explain knocking, properties and its effects in ci engine. Chapter 5 engine performance and efficiency your prime concern as an engineman is to keep the machinery for which you are responsible operating in the most efficient manner possible. Influence of compression ratio on the performance characteristics of a spark ignition engine aina t.

From the above discussion on knock, it may be seen that four major factors are involved in either producing or preventing knock. The expansion ratio which may or may not equal to the compression ratio determines how much work is. The usage of hydrogen in compression ignition engine leads to production of. New model for knock factors optimization in internal. In an internal combustion engine, scavenging is the process of replacing the exhaust gas in a cylinder with the fresh airfuel mixture or fresh air, in the case of directinjection engines for the next cycle. What is knocking and detonation in the petrol and diesel. Knock onset, knock intensity, superknock and preignition in spark. A study on performance and emissions of a 4stroke ic engine operating on landfill gas with the addition of h2, co and syngas a thesis submitted in partial fulfillment of the requirements for the degree of master of science earth and environmental engineering jechan lee dr.

What is the difference between knocking and detonation in. The engine knock analysis an overview sciencedirect. If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, leading to reduced power output. The expansion ratio which may or may not equal to the. Turbulence and engine speedturbulence and engine speed 555.

Curve fitting technique was used in construction of the model, and also akaike information criterion aic was used as a test in choosing the best model. Detonation or engine knocking is when the airfuel mixture does not burns in the cylinder at the time of firing from spark plug but still some airfuel mixture burns in some other part of cylinder, normally outside the normal fuel burn envelope. Then, influencing factors of autoignition and pressure oscillations are presented based on. For a cylinder 10 cm in diameter, the time required for a pressure disturbance. Knock intensity distribution and a stochastic control. Knocking is due to auto ignition of end portion unburned charge in combustion chamber. Factors influencing combustion engine speed equivalence ratio residual gas fraction. Engine trouble, engine knocking, factors affecting knocking. Fuel should burn in even waves that are timed to the engine s cycles, carrying through until the next cycle causes the next wave.

The main goal of this paper is to construct a new mathematical model and study the behavior of the factors affecting the problem of knocking in internal combustion engines. The engine size has little effect on the delay period in milliseconds. Details of operation for manual transmission vehicles as well as restart procedures. Partthrottle knock is a transient phenomenon and is a nuisance to the driver. Turbulence is induced by inlet flow configuration or squish squish is the rapid radial movement of the gas trapped in between the piston and the cylinder head into the bowl or. A high degree of turbulence is needed to achieve a high flame front velocity. The majority of todays highly efficient gasoline engines utilize downsizing. Factors affecting the problem of knocking have been identified. There is a certain time interval between instant of s. High power output and thermal efficiency this can be achieved by considering the following factors. In the spark ignition engine, fuel and air are mixed before initiating combustion with fuel introduced either in the intake manifold or now commonly in cylinder with direct injection technologies.

In other words diesel oil has low self ignition temperature and short time lag where as petrol have high self ignition temperature and a long ignition lag. Engines aice books lecture notes syllabus part a 2 marks with answers me6016 advanced i. Hydrogen fuel is an effective alternate fuel in making a pollutionfree environment with higher efficiency. Internal combustion engines, lecture 3 ideal cycle analysis. Due to the large variation in fuel quality, a large number of engines now contain mechanisms to detect knocking and adjust timing or boost pressure accordingly in order to offer improved performance on high octane fuels while reducing the risk of engine damage caused by knock while running on low octane fuels. Beyond this, the phenomenon of preignition has been linked to the rise in specific power in gasoline engines for many years. Superknock combustion in highly boosted spark ignition engines with random preignition events. Factors affecting fuel conversion efficiency these ideal engine cycle analysis results show that expansion ratio rc and gas composition through the ratio of specific heats both affect the cycles fuel conversion efficiency because. As a mechanical engineer it is very much essential to have knowledge.

Knocking is characterized by extreme pressure differentials and violent gas vibrations evidenced by audible knock. Knock is an abnormal and stochastic combustion phenomenon which limits the efficiency of spark ignition engines. Preignition knocking knocking is due to autoignition of end portion of. Factors determining antiknocking properties of gaseous fuels in. A change in engine speed, changes temptime and pressuretime relationships. Physical factors affecting ignition delay combustion chamber design spray impingement on the walls effect fuel evaporation and id inc in compression ratio, inc p and t and reduces id reducing stroke volume, inc surface area to volume ratio, inc engine. Factors that effect ignition delay in diesel engine. Use knock sensor to control spark retard so as to operate close to engine knock.

Knock is most critical at wot and at low speed because of its persistence and potential for damage. In order to decrease the tendency of knock it is necessary to decrease the ignition delayand. In ci engines knocking occurs in the beginning of combustion. When the secondary fuel ratio was small, the ch4h2 blend possessed the lowest knocking tendency. The factors affecting the combustion in engine cylinder. Diesel fuel injection systems stages of combustion knocking factors affecting knock. One of the main factors limiting the efficiency of sparkignited engines is the occurrence of engine knock. Superknock combustion in highly boosted spark ignition engines with random preignition events has. It introduces the visualization researches, simulations and some judging indexes of engine knock. 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 aim of this project is detecting knock during combustion of biodieselhydrogen fuel and also the knock is suppressed by timed injection of diethyl ether dee with biodieselhydrogen fuel for different loads. In ci engines diesel is used as fuel, hence they are also called diesel engines. Whether or not knock occurs depends on engine fuel vehicle factors and ambient conditions temperature, humidity. A study on performance and emissions of a 4stroke ic.