Biodiesel, particularly Neem oil-based biodiesel, has emerged as a promising eco-friendly alternative, offering reduced greenhouse gas emissions, lower sulphur content, cleaner combustion, and biodegradability. Variable Compression Ratio (VCR) engines further enhance performance, fuel efficiency, and emissions reduction across various fuels. This study focuses on experimenting with Neem-based biodiesel in VCR engines and conducting a parametric study to address the challenges of fossil fuel use. The experimental study revealed several key findings. CO emissions decreased with higher biodiesel blending and compression ratios, achieving a 28% reduction with NB50 at 6 N-m load and CR 22. CO2 emissions are reduced by 20% using B40 at CR 22 under full load (12 N-m). A 27% reduction in HC emissions is
noted with B30 at CR 20 under full load. NOx emissions increased by 20% at full load and CR 22:1 with pure diesel. Brake Thermal Efficiency increased by 16% with NB30 at 6 N-m loadand CR 22. SFC significantly decreased under no-load conditions with NB50. Optimal results
from AI-TLBO with NB40 fuel and a compression ratio of 22 at no-load showed reductions of 20.20% in CO, 23.84% in CO2, 24.5% in HC, and a 23.1% NOx increase.