Spark ignition engines, knock

Knock in spark ignition engines may be defined as an abnormally rapid combustion of the unburned fuel-air mixture ahead of the normal flame front. A severe pressure unbalance due to this rapid combustion process sets up shock waves which impinge on the cylinder walls and piston and produce the characteristic metallic knocking noise (43). 

Various modifications of the normal spark-ignited engine have been made to increase the utility of the engine as a research tool. Using these modified engines, the chemical and physical phenomena accompanying the knock reactions have been studied in detail. A brief description of these experimental techniques is included in this review. 

Motor octane method a test for determining the knock rating of fuels for use in spark-ignition engines see also Research octane method. 

The autoignition that leads to knock in spark ignition engines is extremely dependent on the chemical composition of the fuel. The knock phenomenon and the practical methods of characterising a fuel in terms of its octane number are described in Chapter 7, but it is pertinent to illustrate here how the understanding of alkane oxidation can help to elucidate the effect of fuel structure on its behaviour in engines. 

Measurements and the Cyclic Dispersion of Knock in Spark Ignition Engines, 25th Symp. (Int.) Comb. (1994) pp. 125-133. 

R.J. Nates and A.D.B. Yates, Knock Damage Mechanisms in Spark-Ignition Engines, SAE Technical Paper 942064 (1994). 

D. Bradley, G.T. Kalghatgi, C. Morley, P. Snowdon and J. Yeo, CARS Temperature Measurements and the Cyclic Dispersion of Knock in Spark Ignition Engines, 25th Symp. (Int.) Comb. (The Combustion Institute, Pittsburgh, 1995) p. 125. 

D. Lyon, Knock and Cyclic Pressure Dispersion in a Spark Ignition Engine, Petroleum Based Fuels and Automobile Applications, I. Mech. Eng. Lon. (1986) 105. 

G.T. Kalghatgi, P. Snowdon and C.R. McDonald, Studies of Knock in a Spark Ignition Engine with CARS Temperature Measurements and Using Different Fuels, SAE Technical Paper 950690 (1995). 

O.K.L. Lee and N.S. Lightfoot, Investigation of Flame Propagation Leading to the Knock Phenomenon in Spark Ignition Engine, Combustion Research Conference, 18/19 March 1986 (Publications Office, Harwell Laboratory, 1986) p. 134. 

G.T. Kalghatgi, M. Golombok and P. Snowdon, Fuel Effects on Knock, Heat Release and CARS Temperatures in a Spark Ignition Engine, Comb. Sci. Tech. 110-111 (1995) 209. 

G.T. Kalghatgi, Combustion Chamber Deposits and Knock in a Spark Ignition Engine - Some Additive and Fuel Effects, SAE paper No. 962009 (1996). 

C.A. Blunsdon and J.C. Dent, The Simulation of Autoignition and Knock in a Spark Ignition Engine with Disk Geometry, SAE Technical Paper 940524 (1994). 

Theoretical air/fuel ratio - A = 14.5 kg air by kg fuel. Octane number (RON) - 92 - 98 this is a measure of autoignition resistance in a spark-ignition engine, being the volume percentage of iso-octane in an iso-octane/ n-heptane mixture having the same anti-knocking... 

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