Optical study of knocking phenomenon in a spark-ignition engine by using high-speed OH* chemiluminescence imaging: A multiple ignition sites approach

<div class="section abstract"><div class="htmlview paragraph">Ammonia (NH<sub>3</sub>) is a carbon-free fuel, which could partially or completely eliminate hydrocarbon (HC) fuel demand. Using ammonia directly as a fuel has some challenges due to its low burning speed and low flammability range, which generates unstable combustion inside the combustion chamber. This study investigated the effect of two different compression ratios (CRs) of 10.5 and 12.5 on the performance of ammonia combustion by using a conventional single spark-ignition (SI) approach. It was found that at a lower CR of 10.5, the combustion was unstable even at advanced spark timing (ST) due to poor combustion characteristics of ammonia. However, increasing the CR to 12.5 improved the engine performance significantly with lower cyclic variations. In addition, this research work also observed the effect of multiple spark ignition strategies on pure ammonia combustion and compared it with the conventional SI approach for the same operating conditions. Multiple flames were generated by four spark plugs, which were mounted at equal intervals on the periphery of a customized metal liner and one additional spark plug was fitted at the top of the cylinder head. The results illustrated that adding more spark ignition sites builds higher in-cylinder pressure and temperature, which further burned the charge rapidly. This produced higher engine efficiency, lower combustion duration, and reduced cycle-to-cycle variations. Additionally, multiple spark plugs together were used to ignite a lean case of air-fuel equivalence ratio, λ: 1.2, and compare it with the stoichiometry condition of λ: 1.0. Furthermore, a Cambustion fast NO and NO<sub>2</sub> analyzer was used to precisely record the NO and NO<sub>2</sub> concentrations during ammonia combustion. It was observed that firing multiple spark plugs produced higher NOx emissions than the single spark plug case, considered to be due to the higher in-cylinder temperature generated by the creation of multiple flame kernels.</div></div>

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A Comparative Study of Knock Formation in Gasoline and Methanol Combustion Using a Multiple Spark Ignition Approach: An Optical Investigation

Uddeen,

Tang,

Shi

et al. 2024

SAE Technical Paper Series

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<div class="section abstract"><div class="htmlview paragraph">Engine knock is a major challenge that limits the achievement of higher engine efficiency by increasing the compression ratio of the engine. To address this issue, using a higher octane number fuel can be a potential solution to reduce or eliminate the propensity for knock and so obtain better engine performance. Methanol, a promising alternative fuel, can be produced from conventional and non-conventional energy resources, which can help reduce pollutant emissions. Methanol has a higher octane number than typically gasolines, which makes it a viable option for reducing knock intensity. This study compared the combustion characteristics of gasoline and methanol fuels in an optical spark-ignition engine using multiple spark plugs. The experiment was carried out on a single-cylinder four-stroke optical engine. The researchers used a customized metal liner with four circumferential spark plugs to generate multiple flame kernels inside the combustion chamber. The results indicated that generating multiple flames inside the cylinder caused higher pressures and temperatures, which led to the production of more knocking cycles with higher knock intensities. Additionally, the study showed that methanol combustion produced significantly lower knock intensity with better engine power output compared to gasoline combustion due to its higher octane rating enabling more advanced ignition and its faster flame propagation. The researchers characterized various knock intensities obtained by multiple ignition sites and exhibited a transition from normal combustion to slight knock, medium knock, and high knock cases. Furthermore, the researchers performed high-speed natural-flame-luminosity (NFL) imaging to capture the multiple flame development and autoignition kernels inside the cylinder for various combustion cases. This study provides a detailed understanding of the combustion characteristics of gasoline and methanol fuels in a spark-ignition engine and can be used to further optimize engine performance by reducing knock intensity and increasing engine efficiency.</div></div>

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Optical study of knocking phenomenon in a spark-ignition engine by using high-speed OH* chemiluminescence imaging: A multiple ignition sites approach

Cited by 3 publications

References 37 publications

A novel multiple spark ignition strategy to achieve pure ammonia combustion in an optical spark-ignition engine

A novel multiple spark ignition strategy to achieve pure ammonia combustion in an optical spark-ignition engine

Investigation into Various Strategies to Achieve Stable Ammonia Combustion in a Spark-Ignition Engine

A Comparative Study of Knock Formation in Gasoline and Methanol Combustion Using a Multiple Spark Ignition Approach: An Optical Investigation

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