Cycle-to-Cycle Pressure Analysis of Butanol-Water-Diesel Blends at Varying Engine Loads

Abstract

This study investigates the cycle-to-cycle variation (CCV) in-cylinder pressure for an internal combustion engine fueled with various butanol–water–diesel blends at a constant engine speed of 3,000 rpm and different engine loads (20% and 35%). The primary aim is to assess the combustion stability and performance of the tested emulsified fuels by analysing in-cylinder pressure and coefficient of variation (COV) of the indicated mean adequate pressure (IMEP). Five fuel types were tested: pure diesel (D), water-emulsified diesel (W5D), and three water–diesel blends with 5%, 10%, and 15% butanol additions (W5DBu5, W5DBu10, W5DBu15). At 20% engine load, the W5DBu5 blend showed the lowest relative standard deviation (%RSD) of maximum pressure at 2.80%, indicating superior combustion stability compared to diesel (5.58%) and W5D (4.77%). The maximum pressure (Pmax) ranged from 47.68 bar (D) to 67.30 bar (W5DBu15). At 35% load, W5DBu10 exhibited the highest Pmax of 81.34 bar and a higher variation (%RSD of 2.93%), while diesel had a significantly lower variation at 1.45%. The results demonstrate that small additions of butanol, especially in W5DBu5, improve pressure stability and combustion performance at partial load. However, increased butanol concentration beyond 10% tends to elevate cyclic pressure fluctuations. These findings offer insight into optimizing biofuel blends for improved engine efficiency and reduced emissions.