Systematic Approach to Analyze and Characterize Pre-ignition Events in Turbocharged Direct-injected Gasoline Engines

Abstract

Downsized direct-injected boosted gasoline engines with high specific power and torque output are leading the way to reduce fuel consumption in passenger car vehicles while maintaining the same performance when compared to applications with larger naturally aspirated engines. These downsized engines reach brake mean effective pressure levels which are in excess of 20 bar. When targeting high output levels at low engine speeds, undesired combustion events called pre-ignition can occur. These pre-ignition events are typically accompanied by very high cylinder peak pressures which can lead to severe damage if the engine is not designed to withstand these high cylinder pressures. Although these pre-ignition events have been reported by numerous other authors, it seems that their occurrence is rather erratic which makes it difficult to investigate or reliably exclude them. This paper describes a systematic engine dyno testing approach to force the engine into pre-ignition in order to study and characterize these events. A sensitivity study of various parameters shows that pre-ignition can occur repeatedly at the same load levels if boundary conditions are controlled sufficiently, meaning pre-ignition occurrence is less erratic than previously thought. Several hundred pre-ignition events have been recorded and analyzed in this study. A post-processing tool was developed and applied to analyze and characterize all recorded pre-ignition events. The knowledge gained out of these investigations will help to better understand the pre-ignition phenomena and what combustion development activities need to be applied in order to avoid or counteract pre-ignition during an engine development program or afterwards during customer usage in a passenger car.

LES study of deflagration to detonation mechanisms in a downsized spark ignition engine

“…Flame speeds between 1 and 2 km/s were measured in some specific super-knock operating conditions [5,6], which are at least two orders of magnitude larger than the turbulent premixed flame speed. Besides, the pressure levels recorded by pressure transducers indicate that the pressure rise can be sometimes larger than the constant volume pressure increase observed in a homogeneous autoignition [4]. These observations suggest that super-knock is characterized by a deflagration to detonation transition (DDT).…”

“…On the other hand, pre-ignition, also called LSPI (Low Speed Pre-Ignition) [2] corresponds to the autoignition of a fresh gases spot before ST that acts as a spark plug itself, leading to the creation of a premixed flame before ST. A pre-ignition cycle can be schematically understood as a cycle experiencing a very early ST as experimentally shown in [2]. As the premixed flame develops earlier in a pre-igniting cycle (or with a very early ST), autoignition of the end gas is often observed, but not systematically [3,4]. If this autoignition event is weak, it is similar to knock under standard spark ignition, this is why it is still called knock.…”

“…If this autoignition event is weak, it is similar to knock under standard spark ignition, this is why it is still called knock. On the contrary, extremely strong autoignitions can be observed at a very low frequency, leading to a fast and intense pressure rise [2][3][4]. Physically, this means that a large amount of fresh gases autoignites suddenly, leading to extreme pressure levels reaching several hundred bars.…”

Simulations of engine knock flow field and wave-induced fatigue of a downsized gasoline engine

“…At present, super detonation has become the biggest obstacle for gasoline engines to continue to improve power density and reduce fuel consumption. Many automotive engine manufacturers, fuel and lubricant companies and related research institutes at home and abroad are studying the mechanism and suppression strategy of super detonation [2,3]. Under this circumstance, the study of the engine knock characteristics and piston strength calibration has both theoretical and engineering values in terms of the research for safety and reliability of the downsized engine [4].…”

Probabilistic Approach to Predict Abnormal Combustion in Spark Ignition Engines

“…The source that a causes pre-ignition is not known in experiments and multiple sources are reported in literature that is responsible for preignition, such as oil droplets, carbon deposits, hot surfaces etc., [4,[12][13][14][15][16]. However, it is important to realize that whether the preignition leads to detonation/super-knock in the end gas depends strongly on the property of the bulk gas, such as temperature and composition distribution.…”