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. Factors determing ignition and efficient combustion in modern. As a mechanical engineer it is very much essential to have knowledge. 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. Engines mechanical engineering multiple choice questions and answers list. Study of knocking effect in compression ignition engine. Particularly for spark ignition engines a high octane number of fuel is needed for. The factors which affect the flame propagations are the factors wh ich affect the flame propagations are ich affect the flame propagations are 111. The effects of detonation may be anywhere from arbitrary to severe. Higher combustion efficiency and fuel economy can be achieved by higher flame propagation velocities. Knock is most critical at wot and at low speed because of its persistence and potential for damage. A change in engine speed, changes temptime and pressuretime relationships. The most important factors which affect the flame speed are. Details of operation for manual transmission vehicles as well as restart procedures.
Fuel consumption of engine increases drastically as heat energy is lost during knocking. This is not acceptable and causes harm to the engine. 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. Describe a 3 explain knocking, properties and its effects in ci engine. The same reason also affects the power output which is observable at the time of acceleration. Hydrogen is one of two natural elements that combine to make water.
Knock onset, knock intensity, superknock and preignition in spark. Knocking is due to auto ignition of end portion unburned charge in combustion chamber. Knocking is characterized by extreme pressure differentials and violent gas vibrations evidenced by audible knock. 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. The usage of hydrogen in compression ignition engine leads to production of. In this article, i am going to explain the various factors which will affect the combustion process. In ci engines knocking occurs in the beginning of combustion. A high degree of turbulence is needed to achieve a high flame front velocity.
Factors influencing combustion engine speed equivalence ratio residual gas fraction. 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. It introduces the visualization researches, simulations and some judging indexes of engine knock. Spark ignition engine an overview sciencedirect topics. If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, leading to reduced power output. A knocking sound is the most typical engine noise indicating a mechanical problem that can be fixed if diagnosed correctly and early. 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. The expansion ratio which may or may not equal to the. Then, influencing factors of autoignition and pressure oscillations are presented based on.
Influence of compression ratio on the performance characteristics of a spark ignition engine aina t. What is knocking and detonation in the petrol and diesel. There is a certain time interval between instant of s. Turbulence and engine speedturbulence and engine speed 555. Performance of an automobile engine is based on the various factors that affect combustion in engines. High mean pressures produce increased knocking, which frequently results in a reduction in the compression ratio at high specific powers. Knock is an abnormal and stochastic combustion phenomenon which limits the efficiency of spark ignition engines. Partthrottle knock is a transient phenomenon and is a nuisance to the driver.
The majority of todays highly efficient gasoline engines utilize downsizing. Certain chemical changes must first occur for knock to happen. The factors which affect the flame propagations are 1. The factors affecting the combustion in engine cylinder. 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 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. In order to decrease the tendency of knock it is necessary to decrease the ignition delayand. Beyond this, the phenomenon of preignition has been linked to the rise in specific power in gasoline engines for many years. Engines aice important part b 16 marks questions, pdf books, question bank with answers key, me6016. Pdf knocking combustion in sparkignition engines researchgate. 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. 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. The expansion ratio which may or may not equal to the compression ratio determines how much work is.
The highpressure and hightemperature of the compression stroke combine with the internal heat to. For a cylinder 10 cm in diameter, the time required for a pressure disturbance. New model for knock factors optimization in internal. Knock intensity distribution and a stochastic control. A sdvosb service disabled veteran owned small business. Factors determining antiknocking properties of gaseous fuels in spark ignition. Engine trouble, engine knocking, factors affecting knocking. Factors determining antiknocking properties of gaseous fuels in. Similarly, overheating may cause additional wearandtear on the engine, be relatively harmless or cause the engine to catch on fire and break.
Knocking in your engine, also described as pinging, can mean one of several problems. Internal combustion engines, lecture 3 ideal cycle analysis. Fuel should burn in even waves that are timed to the engine s cycles, carrying through until the next cycle causes the next wave. 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. Hydrogen fuel is an effective alternate fuel in making a pollutionfree environment with higher efficiency. Engines mechanical engineering multiple choice questions and answers list sunday, 31 august 2014 250 top i. Factors affecting the problem of knocking have been identified. Diesel fuel injection systems stages of combustion knocking factors affecting knock. The engine knock analysis an overview sciencedirect. 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.
Superknock combustion in highly boosted spark ignition engines with random preignition events. When the secondary fuel ratio was small, the ch4h2 blend possessed the lowest knocking tendency. 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. Detection and control of knocking combustion have become essential components of control systems in modern engines. Preignition knocking knocking is due to autoignition of end portion of. 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 ci engines diesel is used as fuel, hence they are also called diesel engines. Knocking combustion in sparkignition engines sciencedirect. 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. From the above discussion on knock, it may be seen that four major factors are involved in either producing or preventing knock. Higher intake air temperatures increase the occurrence of engine knock. High power output and thermal efficiency this can be achieved by considering the following factors.
Factors that effect ignition delay in diesel engine. The ambient temperature is found to affect the flame speed, the combustion reaction rate, the uniformity of the fuelair mixture, the volumetric efficiency and the heat transfer rate though the cylinder walls pulkrabek, 1997. Noted below are a few facts about why an engine knocks and what can be done to resolve these issues. Effect of knocking in spark ignition in a fourstroke engine. The engine size has little effect on the delay period in milliseconds. What is the difference between knocking and detonation in. 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. The high pressure and hightemperature of the compression stroke combine with the internal heat to. Engines aice books lecture notes syllabus part a 2 marks with answers me6016 advanced i. One of the main factors limiting the efficiency of sparkignited engines is the occurrence of engine knock. What are the various factors that affect the flame speed. 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. Whether or not knock occurs depends on engine fuel vehicle factors and ambient conditions temperature, humidity. This video explains knocking combustion and preignition and the reasons for this irregular combustion.