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

Singh, Eshan; Hlaing, Ponnya; Shi, Hao; Dibble, Robert W.

doi:10.4271/2019-01-0257

Cited by 16 publications

(11 citation statements)

References 49 publications

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“…In previous work, we direct-injected water late in the exhaust stroke to cool/quench only the residual exhaust without impacting the fresh incoming mixture (by finishing water injection before intake valve opening time) [23,24]. Such strategy significantly suppressed preignition frequency, supporting the idea that reactive debris in the residual gas is the cause for triggering pre-ignition in the subsequent cycle.…”

Section: Results and Discussion: Exploration #1: Pre-ignition Prediction From Exhaust Cycle Ion Signal And Mitigation Strategymentioning

confidence: 61%

Pre-ignition Detection Followed by Immediate Damage Mitigation in a Spark-Ignited Engine

Singh

Dibble

2021

SAE Technical Paper Series

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Pre-ignition remains a significant bottleneck to further downsizing and downspeeding technologies employed for reducing CO2 emissions in modern turbocharged spark-ignited engines. Pre-ignition, which occurs rarely, may lead to high peak pressures that auto-ignite the entire charge before TDC. The resulting high-pressure oscillations are known as super-knock, leading to sudden and permanent hardware damage to the engine. Over the years, numerous researchers have investigated the stochastic phenomenon's source and concluded that there is a role of lubricant additives, deposits, gasoline properties, and hot surfaces in triggering pre-ignition. No single source has been identified; the research continues. Here, we take a different approach; rather than continue the search for the source(s) of super-knock, we explore mitigating super-knock by detecting pre-ignition early enough to take immediate evasive action. Such evasive action is expected to suppress knock intensity, thereby saving the engine from any permanent damage.In this regard, the current work offers ways to detect pre-ignition (using ion sensors) and then mitigate engine damage by using immediate fuel enrichment. We present three related explorations.In exploration #1, we explore if the occurrence of ions products from the exhaust can warn that the next cycle has a high probability of preignition. For this next cycle, the intake fuel injection can be suspended or increased to operate engine fuel-rich. We find strong ion activity on every cycle. However, there is a weak correlation between the ion signal and pre-ignition occurrence.In exploration #2, an in-cylinder ion-current sensor is used to discover pre-ignition event unfolding during the compression stroke. When such a rare event is detected, more fuel is immediately injected, making the end gas far less reactive and avoiding autoignition and knock. These explorations #1 and #2 were conducted with a DC-based ion sensor. These explorations showed exciting and promising findings. However, our DC-based ion sensors are prone to low signal-to-noise ratio SNR, leading to false positives (unacceptably high number of false positives.)In Exploration #3, the signal-to-noise ratio improvement is explored by replacing the DC-based system with a novel AC-based system. We find the bandpass filtering of the ion signal is key to improved SNR.

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Section: Results and Discussion: Exploration #1: Pre-ignition Prediction From Exhaust Cycle Ion Signal And Mitigation Strategymentioning

confidence: 61%

Pre-ignition Detection Followed by Immediate Damage Mitigation in a Spark-Ignited Engine

Singh

Dibble

2021

SAE Technical Paper Series

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“…Water injection has been explored further, concerning its preignition suppression tendency in a previous work . Key findings relevant to the preignition suppression by water injection are discussed here.…”

Section: Resultsmentioning

confidence: 97%

“…Water injection at −50 CAD aTDC was not effective beyond intake air pressure 1.07 bar case. Previously, the authors have observed that injecting water very close to the top dead center may not allow the best charge cooling because of incomplete evaporation by the time of spark . Representative data for only two cases: intake air pressure of 1.60 and 1.80 bar are shown in the results below.…”

Section: Resultsmentioning

confidence: 99%

Investigating Water Injection in Single-Cylinder Gasoline Spark-Ignited Engines at Fixed Speed

2020

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Increasingly stringent emission norms have always brought forth innovative measures to improve engine efficiency. Spark-ignited engines have been limited in efficiency, traditionally by knock, and more recently by preignition too. Water injection has recently regained interest as a knock suppressant. The current work explored water injection via port and direct injection at a fixed engine speed of 2000 rpm and varying engine loads. The data presented in this work emphasize that the gains from using water injection are best realized at a specific injection timing (neither too early nor too late), and the effectiveness of water in suppressing knock decreases rapidly with increasing water mass injected. In general, direct water injection offers a more significant knock reduction because of better utilization of the charge cooling effect than port water injection. Engine-out emission confirms a reduction in NOx and CO, while the HC emissions increased when using water injection. No preignition events were observed at the engine load up to 27 bar. Chemical kinetics simulations confirm the role of water in suppressing reactivity under the operating conditions considered in the current study.

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“…It also appears to confirm the link between the previous cycle and pre-ignition event, which has been the subject of some debate within the research community. More details on the experiment are part of [36].…”

Section: Effect Of Injecting Water Late In the Exhaust Strokementioning

confidence: 99%

Mechanism Triggering Pre-Ignition in a Turbo-Charged Engine

Singh

Dibble

2019

SAE Technical Paper Series

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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).

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

Cited by 16 publications

References 49 publications

Pre-ignition Detection Followed by Immediate Damage Mitigation in a Spark-Ignited Engine

Pre-ignition Detection Followed by Immediate Damage Mitigation in a Spark-Ignited Engine

Investigating Water Injection in Single-Cylinder Gasoline Spark-Ignited Engines at Fixed Speed

Mechanism Triggering Pre-Ignition in a Turbo-Charged Engine

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