Influence of Ethanol Blends on Low Speed Pre-Ignition in Turbocharged, Direct-Injection Gasoline Engines

Pre-ignition is an abnormal engine combustion phenomenon where the inducted fuel-air charge ignites before the spark ignition. This premature combustion phenomenon often leads to heavy knocking events. The mixture preparation plays a critical role in pre-ignition tendency for a given load. Literature shows efforts made towards improving pre-ignition-limited-IMEP by splitting the injection pulse into multiple pulses. In this study, two direct injectors are used in a single cylinder research engine. A centrally mounted direct injector was used to inject Coryton Gasoline (RON 95) fuel early in the intake stroke. A second fluid was injected late in the compression stroke to suppress pre-ignition. The fluids used in the second direct injector was varied to see the effects of the molecule and its physical and chemical property on pre-ignition suppression tendency. Methanol, ethanol, water, and gasoline were tested as second fluid. Engine tests were conducted at 2000 rpm and at an intake pressure of 2.1 bar (abs). Although alcohols show high pre-ignition tendency as fuels, they were most effective at pre-ignition suppression when injected later in the compression stroke. The pre-ignition suppression led to a decrease in IMEP and an increase in cycle-to-cycle variation. Water injection was highly effective at maintaining peak IMEP values. Water injection was further explored for pre-ignition suppression. The water injection helped reduce pre-ignition count when injected at two different injection times each in intake, compression and late exhaust stroke.

Section: Effect Of Varying Fluids In Late Split Injection Pulsementioning

confidence: 99%

“…For the third case, water was injected into the exhaust stroke. Recent research elucidates that pre-ignition precursors may miss the scavenging process and be trapped in the cylinder [3,54,56,57]. These particles can trigger pre-ignition in the next cycle.…”

Section: Effect Of Water Injection On Pre-ignition Suppressionmentioning

confidence: 99%

Effect of Different Fluids on Injection Strategies to Suppress Pre-Ignition

Singh¹,

Hlaing²,

Shi³

et al. 2019

“…A connection between pre-ignition events and combustion events in previous cycles has been observed. Haenel et al (2017) provided evidence of elevated hydrocarbon emissions in the exhaust from the cycle before a pre-ignition cycle [13]. Consecutively, Ford Motors were able to trigger pre-ignition in cycles after a highly retarded spark timing cycle.…”

Section: Introductionmentioning

confidence: 99%

“…It should be noted that pre-ignition and super-knock are phenomenologically different [11,12]. While pre-ignition is a hot-spot induced ignition phenomenon (more frequent at low speeds), super-knock is auto-ignition of end-gas [13]. In general, super-knock is always preceded by a pre-ignition event, but a pre-ignition event does not guarantee a super-knock event.…”

Section: Introductionmentioning

confidence: 99%

Mechanism Triggering Pre-Ignition in a Turbo-Charged Engine

Singh

Dibble

2019

Pre-ignition in modern engines is largely attributed to oil-fuel mixture droplets igniting before the spark timing. Researchers have also found pre-ignition events to be triggered by high hydrocarbon emissions from the previous cycle as well as late spark timing in the previous cycle. Additionally, an ideally scavenged engine was not found to be limited by pre-ignition. These observations point to a significant role of residuals in triggering pre-ignition events. Current work studies preignition in a probabilistic approach. The effect of residuals and incylinder thermodynamic state is studied by varying the exhaust back pressure and intake air temperature respectively. Experiments were performed with a fixed mass flow rate of air + fuel and intake air temperature while the exhaust back pressure was varied. Intake air pressure varied in response to fixed intake temperature. Pre-ignition and super-knock count increased with increasing exhaust back pressure. In the next set of experiments, mass flow rate of air + fuel and intake air pressure were fixed, while the exhaust back pressure was varied. Intake air temperature was varied to fix the intake air pressure constant. Pre-ignition counts generally increased with increasing intake temperature, although the exhaust back pressure decreased. Number of super-knock cycles correlated directly with intake air temperature. Conclusively, the current study shows that probability of a pre-ignition event relies on (a) the likelihood of precursor generation (from fuel impinging the liner), (b) the likelihood of precursors being held back in cylinder (related to exhaust back pressure) and (c) the reactivity of bulk mixture (related to in-cylinder temperature).

“…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.…”

Section: Introductionmentioning

confidence: 99%

Probabilistic Approach to Predict Abnormal Combustion in Spark Ignition Engines

Ali¹,

Luong²,

Sow³

et al. 2018

This study presents a computational framework to predict the outcome of combustion process based on a given RANS initial condition by performing statistical analysis of Sankaran number, Sa, and ignition regime theory proposed by Im et al. [1]. A criterion to predict strong auto-ignition/detonation a priori is used in this study, which is based on Sankaran-Zeldovich criterion. In the context of detonation, Sa is normalized by a sound speed, and is spatially calculated for the bulk mixture with temperature and equivalence ratio stratifications. The initial conditions from previous pre-ignition simulations were used to compute the spatial Sa distribution followed by the statistics of Sa including the mean Sa, the probability density function (PDF) of Sa, and the detonation probability, P D. Sa is found to be decreased and detonation probability increased significantly with increase of temperature. The statistic mean Sa calculated for the entire computational domain and the predicted Sa from the theory were found to be nearly identical. The predictions based on the adapted Sankaran-Zel'dovich criterion and detonation probability agree well with the results of the previous high fidelity pre-ignition simulations.