The objective of the present investigation is to explore the influence of ternary (diesel-biodiesel-alcohol) fuel blends on the combustion and vibration parameters of a variable compression ratio compression ignition engine. Kusum seed oil biodiesel and isobutyl alcohol were blended with conventional diesel to make a ternary fuel. The blend of biodiesel-diesel (B20) was made in proportion of 20% and 80% by volume, respectively. Furthermore, isobutyl alcohol was added at diverse proportions (ie, 0.25%, 0.5%, 0.75%, and 1%). The investigation was carried at different compression ratios (CRs), namely, 16.5, 17.5, and 18.5. The study shows that, upon the addition of isobutyl alcohol, the combustion characteristics (ie, cylinder pressure [CP] and net heat release rate [NHRR]) are significantly enhanced, whereas the mechanical vibration level maintains stable. The CP and NHRR of B20+ 1% isobutyl alcohol are greatly improved for corresponding values of 4.55% and 8.39%, respectively, except for the conventional diesel at CR 18.5. Furthermore, the root mean square velocity (vibration) decreases when increasing the quantity of isobutyl alcohol and attained a minimum with B20+ 1% isobutyl alcohol. The experimental results show that the isobutyl alcohol up to 1% with diesel-biodiesel blends can be used in the CI engine with no further adjustments. K E Y W O R D S combustion, compression ratio, Kusum seed oil biodiesel, RMS velocity, transesterification Abbreviations: , crank angle (•); l, length of connecting rod (m); ΔCA, uncertainty in crank angle; ΔW, uncertainty in load; ΔP, uncertainty in pressure; ΔN, uncertainty in speed; ΔT, uncertainty in temperature; ΔRMSvelocity, uncertainty in vibration; ADC, analog to digital converter; B20, KSOME 20% in diesel; CHRR, net heat release rate (J/ o CA); CI, compression ignition; CP, cylinder pressure (bar); CR/CRs, compression ratio/compression ratios; D, cylinder bore (m); FFT, fast Fourier transforms; IP, injection pressure; KSOME, Kusum seed oil methyl ester; LDV, laser Doppler vibrometer; m/sec, meter/second; n, number of points within a time period; NaOCH 3 , sodium methoxide; NHRR, cumulative heat release rate (J/ o CA); PDV, Polytec Doppler vibrometer; r, crank radius (m); RMS, root mean square; V, instantaneous cylinder volume (m3); V(t j), velocity with respect to time; Vc, clearance volume (m3); VCR, variable compression ratio; V RMS , RMS velocity. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.