The noise of diesel engines is dependent upon numerous factors such as: load, speed, fuel injection strategies and fuel type, design of the piston, piston-pin and cylinder and their tolerances, bearings, valves and rocker arm clearances, and designs of the manifolds.
In this study, engine sound and vibrations analysis have been conducted using two types of fueling and combustion strategies: classical ULSD combustion and the new RCCI with n-butanol injected in the intake manifold. The analyses add to the understanding of the influence of combustion characteristics’ effect on mechanical noise and vibrations throughout the engine’s operating cycle.
The sound and vibration signals were both analyzed in the frequency and angle domain spectrum. Overall NVH spectrum from ULSD combustion was compared to that of RCCI with 50% by mass PFI of n-butanol (the 50% remaining ULSD fuel was directly injected).
Frequency analyses were performed using the FFT and CPB methods with Bruel & Kjaer’s Pulse sound and vibrations analysis software. Angle domain analyses were performed, referencing 0 CAD as TDC in combustion.
The engine tests were conducted at 1500 rpm and 4 bar IMEP. The COV of IMEP for DI ULSD and RCCI were 2.4 and 2.2, respectively. The correlations between sound, three dimensional vibration levels, and timings were found for: pressure gradients from combustion process, intake and exhaust valve actuations and gas exchange, and piston slap on the cylinder liner.
The measurements were extracted and analyzed, and the results determined that virtually all the noise and vibration values pertinent to RCCI were lower than those of ULSD classical combustion.