Experimental Investigation of Cycle-to-Cycle Variations in Homogeneous Charge Compression Ignition Engine Fueled with Methanol Using Wavelets

Abstract

<div class="section abstract"><div class="htmlview paragraph">The development of automotive engines continues to be determined by gradually more stringent emission norms including CO₂ emissions and fuel consumption. To fulfill the simultaneous emission requirements for near-zero pollutants and low CO₂ levels, several research studies are currently being carried out around the world on new engine combustion process, such as Homogeneous Charge Compression Ignition (HCCI). In HCCI engines, combustion rate, and ignition timing are dominated by physical and chemical properties of fuel/air/residual gas mixtures, boundary conditions including ambient temperature, pressure, and humidity, and engine operating conditions such as load, speed, etc. Higher cycle-to-cycle variations are observed in HCCI combustion engines due to the large variability of these factors. The cyclic variations in the HCCI engine are investigated on a modified four-stroke, four-cylinder engine. The HCCI combustion mode is tested with methanol fuel. This study presents the cyclic combustion analysis of the HCCI engine using statistical and Wavelet Transform techniques. The cyclic variations are characterized under different operating conditions such as relative air-fuel ratios (λ), intake air temperature (<b><i>T</i></b>_{<b><i>i</i></b>}), and engine speed (N). The wavelet analysis results indicate that cyclic variations in IMEP and combustion phasing (CA₅₀) occur at different frequencies. Results indicate that with an increase in the T_i, the variations in IMEP are shifted from low periodicity to high periodicity. The high periodicity variations for higher Ti operation are found due to the too advanced CA₅₀ position (before TDC position). Global wavelet spectrum results depict that peak power decreases with an increase in T_i and λ which implies the reduction in cyclic combustion variations.</div></div>