High-frequency Pressure Oscillations Research Articles

A Pressure-Oscillation-Based RON Estimation Method for Spark Ignition Fuels beyond RON 100

Knock in spark ignition (SI) engines occurs when the air–fuel mixture in the combustion chamber ignites spontaneously ahead of the flame front, reducing combustion efficiency and possibly leading to engine damage if left unattended. The use of knock sensors to prevent it is common practice in modern engines. Another measure to mitigate knock is the use of higher-octane fuels. The American Society for Testing and Materials’ (ASTM) determination of the Research Octane Number (RON) and Motor Octane Number (MON) of spark ignition fuels has been based on measuring cylinder pressure rise at the onset of knock since its inception in the 1930s. This is achieved through a low-pass filtered pressure signal. Knock detection in contemporary engines, however, relies on measuring engine vibrations caused by high-frequency pressure oscillations during knock. The difference between conditions in which fuels are evaluated for their octane rating and the conditions that generate a knock intensity signal from the knock sensor suggests a potential difference between octane rating and the knock limit typically identified by a contemporary knock sensor. To address this disparity, a modified RON measurement method has been developed, incorporating pressure oscillation measurements. This test method addresses the historical lack of correlation between RON and high-frequency pressure oscillation intensity during knock. Using toluene standardization fuels (TSFs) as a reference, the obtained results demonstrate excellent high-frequency knock intensity-based RON estimations for gasoline. The method is able to differentiate between two fuels that share the same ASTM RON, associating them with a RON-like metric that is more aligned with their performance in a modern SI engine. This alternative method could potentially serve as a template for an upgrade to the existing ASTM RON method without significantly disrupting the current approach. Additionally, its capability to evaluate fuels beyond RON 100 opens the door to assessing a wider range of fuels for antiknock properties and the intensity of fuel oscillations during knocking combustion.

Analysis of the Vibrational Behavior of dual-fuel RCCI combustion in a Heavy-Duty Compression Ignited Engine fueled with Diesel-NG at Low Load

In the field of internal combustion engines, the Low Temperature Combustions (LTC) appear to have the potential to reduce the formation of both soot and nitrogen oxides. One of the most promising LTC is Reactivity Controlled Compression Ignition (RCCI) which is based on the combustion of a lean low reactivity fuel-air mixture generated in the intake manifold and autoignited by small injections of high reactivity fuel introduced at high pressure in the combustion chamber. By the combination of net-zero natural gas and biodiesel, such LTC methodology might represent a suitable solution moving toward zero-emissions in transportation sector.Despite the potential to reduce pollutant emissions, Low Temperature Combustion strategies face a challenge in controlling the angular position where the combustion takes place which can be overcome by a proper management of the high-pressure injections.One potentially interesting application is related to trucks, mainly because they have long periods of idling, since emissions can be drastically reduced by means LTC. A single cylinder research engine for heavy duty application is operated under steady state conditions at low load and speed to analyze the possibility of controlling the engine behavior in dual fuel RCCI mode. The results indicate that the combustion mode switches from the dual-stage to gaussian within a narrow angular range. A further advance of the start of injection can generate misfires and significant variations in typical combustion indexes, while a delayed start of injection can cause impulsive combustion that rises the cylinder temperature and results in high-frequency pressure oscillations inside the combustion chamber. These oscillations are related to the combustion chamber typical resonance frequency, and if relevant in amplitude and persist for a long time, they might generate a potential source of failures.

Wave mode analysis of a turbine guide vane-integrated rotating detonation combustor based on instantaneous frequency identification

Owing to the pressure gain combustion characteristics, the gas turbine can enhance the system thermodynamic cycle efficiency by integrating a rotating detonation combustor (RDC). In this study, an experimental model of a hydrogen/air RDC with a variant installation of turbine guide vanes (TGVs) was developed. A mathematical model was proposed to identify the rotating detonation wave (RDW) propagation direction. The accuracy of the calculated RDW instantaneous velocity was improved, and the range of velocity fluctuations narrowed from 200 to 1700 m s−1 to 800–1600 m s−1. The impact of TGV installation on the rotating detonation characteristics was investigated. Both the RDW frequency and static pressure increased by installing the TGV at the combustor outlet. The propagation direction of the initial detonation wave induced the RDW to propagate along the same direction. TGV installation reduced the discrepancy in the RDW velocity between two opposite directions as well as the propagation direction changing frequency, while the inverse TGV installation achieved better optimization. The high-frequency pressure oscillations attenuated at the downstream of the TGV, and the amplitude varied depending on the TGV installation options. The static pressure decreased by 14%–16% in both TGV installation options when the combustion flow travelled through the TGV.

Structural Characteristics of a Shock Train Flow Field in a Variable Cross-Section S-Shaped Isolator

Experiments were conducted in this study to reveal the flow characteristics of a variable cross-section S-shaped isolator, when applying the steady-state back pressure at the isolator outlet. The self-excited oscillation characteristics of the shock train generated under the influence of steady-state back pressure at an incoming flow speed of Mach 2, were also studied. The findings suggest that pressure oscillation within the area affected by the shock train’s flow field was significantly more potent than outside the affected area. Moreover, the forward movement velocity of the shock train in the variable cross-section S-shaped isolator was not uniform. The forward movement speed was slower when encountering sharp turns and faster during gentle turns. In the shock train flow field, high-frequency pressure oscillations, which mainly stemmed from the oscillations of the separated shock legs, propagated more readily within the flow field than low-frequency pressure oscillations. The significant separation of the shock train flow field will switch between the top and bottom walls, and the frequency of pressure oscillation in the large separation region is low. On another note, the closer the distance between two points is in the shock flow field, the stronger the coherence of pressure oscillations will be. In the distance upstream of the shock train flow field, the turbulent boundary layer (TBL) determines pressure oscillations instead of the shock train flow field, so the coherence was very high.

Experimental and theoretical study on the association between entrainment vortex evolution and pressure oscillation of steam jet condensation

Condensation pressure oscillation of steam jet has great influence on direct contact condensation (DCC) equipment. Therefore, it is essential to reveal the microscopic mechanism of pressure oscillation of steam jet condensation. In this study, the association between entrainment vortex evolution and pressure oscillation of steam jet condensation is investigated. Firstly, the periodic variation of characteristic parameters of jet oscillation caused by periodic vortex shedding is obtained based on the image processing techniques. Secondly, by synchronous comparison between the pressure oscillation cycles and the jet parameters oscillation cycles, it is found that the periodic evolution and shedding of two-phase entrainment vortexes formed in the upper and lower mixing layers is the microscopic mechanism which causes condensation pressure oscillation. Specifically, the high-frequency pressure oscillation near the steam jet results from the high-frequency transverse oscillation of the steam jet which is caused by the periodic vortex evolution in the mixing layer and the periodic shedding of the vortex blob at the tail of the jet; the low-frequency pressure oscillation near the steam jet results from the low frequency oscillation of the whole steam jet caused by periodic shedding of the paired vortex blobs; the pressure oscillation in the downstream of the steam jet is caused by the condensation oscillation of periodic shedding vortex blobs. Finally, the dominant frequency distribution of condensation pressure oscillation under various test conditions is analysed. Combined with the vortex shedding model, a prediction equation of the dimensionless characteristic frequency St of the shedding vortexes is established. The predicted values had good agreement with the experimental results.

Numerical simulation of flow field characteristics and the improvement of pressure oscillation of rotating detonation engine

Due to the inherent working mode of rotating detonation engine (RDE), the detonation flow field has the characteristics of pressure oscillation and axial kinetic energy loss, which makes it difficult to design nozzle and improve propulsion performance. Therefore, in order to improve the characteristics of detonation flow field, the three-dimensional numerical simulation of annular chamber and hollow chamber is carried out with premixed hydrogen/air as fuel in this paper, and then tries to combine the two chambers to weaken the oscillation characteristics of detonation flow field through the interaction of detonation flow field, which is a new method to regulate the detonation flow field. The results show that there are four states of velocity vectors at the outlet of annular chamber and hollow chamber, which makes RDE be affected by rolling moment and results in the loss of axial kinetic energy. In the external flow field of combined chamber, the phenomenon of cyclic reflection of expansion wave and compression wave on the free boundary is observed, which results in Mach disk structure. Moreover, the pressure monitoring points are set at the external flow field. The pressure signal shows that the high-frequency pressure oscillation at the external flow field of the combined chamber has been greatly weakened. Compared to the annular chamber, the relative standard deviation (RSD) has been reduced from 14.6% to 5.6%. The results thus demonstrate that this method is feasible to adjust the pressure oscillation characteristics of the detonation flow field, and is of great significance to promote the potential of RDE and nozzle design.

Experimental Investigation of a Cylindrical Air-Breathing Continuous Rotating Detonation Engine with Different Nozzle Throat Diameters

A continuous detonation engine with various exhaust nozzles, analogous to typical scramjet cavity combustors with variable rear-wall heights, was adopted to perform a succession of cylindrical air-breathing continuous rotating detonation experiments fueled by a non-premixed ethylene/air mixture. The results show that the detonation combustion was observed to self-sustain in the combustor through simultaneous high-speed imaging covering the combustor and isolator. A long test, lasting more than three seconds, was performed in this unique configuration, indicating that the cylindrical isolator–combustor engine exhibits potential for practical applications. Three distinct combustion modes were revealed with varied equivalent ratios (hybrid mode, sawtooth wave mode, and deflagration mode). The diameter of the nozzle throat was critical in the formation of rotating detonation waves. When the nozzle throat diameter was larger than the specific value, the detonation wave could not form and self-sustain. The upstream boundary of the shock train was supposed to be close to the isolator entrance in conditions of a high equivalence ratio and small nozzle throat diameter. In addition, it was verified that periodic high-frequency pressure oscillation could cause substantial impacts on the incoming flow as compared with the steady deflagration with the same combustor pressure.

Characterization of instability mechanisms on sharp and blunt slender cones at Mach 6

Experiments are performed to investigate the effect of nose-tip bluntness on the instability mechanisms leading to boundary-layer transition on a $7^{\circ }$ half-angle cone in a Mach-6 free stream. The development of disturbances is characterized using a combination of high-speed calibrated schlieren images and pressure measurements, and the data are compared with results computed using the parabolized stability equations. The approximately 414 mm long cone model is equipped with an interchangeable nose tip ranging from sharp to 5.08 mm in radius. For nose tips with a radius $R_{N}<2.54\ {\rm mm}$ , second-mode instability waves are the dominant mechanism leading to transition. Time-averaged frequency spectra computed from the calibrated schlieren visualizations and pressure measurements are used to compute the second-mode most-amplified frequencies and integrated amplification rates ( $N$ factors). Good agreement is observed between the measurements and computations in the linear-growth regime for the sharp-nose configuration at each free-stream condition. Additionally, a bispectral analysis identifies quadratic phase locking of frequency content responsible for the growth of higher harmonics. For nose tips of $R_{N}\geqslant 2.54\ {\rm mm}$ , the schlieren visualization region is upstream of the entropy-layer swallowing length, and second-mode waves are no longer visible within the boundary layer; instead, elongated, steeply inclined features believed to be associated with non-modal instability mechanisms develop between the entropy-layer and boundary-layer edges. Simultaneously acquired surface pressure measurements reveal high-frequency pressure oscillations similar to second-mode instability waves associated with the trailing edge of these non-modal features.

Flow features of shallow cylindrical cavities subject to grazing flow

The flow behavior within shallow cavities of circular planform, subject to grazing flows, exhibits a strong dependence on the cavity depth (h)-to-diameter (d) ratio. In the present experimental study, the internal flow patterns within shallow circular cavities having a depth-to-diameter ratio of 0.15 ≤ h/d ≤ 1 have been extracted from mean static and unsteady surface pressure measurements collected on the cavity surfaces. In the literature, no comprehensive experimental study spanning this entire h/d range is available characterizing the flow behavior in shallow cylindrical cavities; only certain aspects of flow at select h/d are present in the current literature, and the present paper addresses this shortcoming. In agreement with the previous research on shallow cylindrical cavities, the mean flow orientation and the amplitude of large-scale pressure fluctuations within the cavity are observed to follow a non-monotonic function as the depth-to-diameter ratio is varied, with h/d = 0.5 exhibiting the greatest asymmetry in flow orientation. The division of the internal cavity flow into stable, switching, and flapping regimes established by previous related studies has been reevaluated, and utilizing a simple filtering technique, a modification to the classification of these flow regimes has been proposed for the present conditions. Furthermore, the observation of two high-frequency pressure oscillations, measured within the cavity for the flapping regime, has been linked to shear layer instabilities.

High-frequency transverse combustion instabilities of lean-premixed multislit hydrogen-air flames

The present experimental investigation is concerned with combustion dynamics of lean-premixed multislit hydrogen-air flames, with the aim of addressing some of the central technical problems associated with the development of low-emission carbon-free gas turbine combustion technology. To mitigate flashback risk in relatively fast premixed hydrogen flames, we use a multislit injector assembly with a slit width of 1.5 mm, of the same order of magnitude as the characteristic thickness of lean-premixed hydrogen flames. This new perspective on the characteristic nozzle dimension makes it possible to scrutinize the dynamics of multisheet hydrogen flames under extreme conditions. We carry out extensive measurements of self-excited pressure oscillations over a broad range of operating conditions between 30 and 100 kW thermal power. The experimental datasets are analyzed using the acoustic wave decomposition method, low-order thermoacoustic network modeling, and FEM-based three-dimensional Helmholtz simulations. We show that lean-premixed multislit hydrogen flames – unlike the multi-element hydrogen-air flame ensembles considered in our earlier investigations – undergo strong high-frequency pressure oscillations between 3.1 and 3.5 kHz in excess of 25 kPa, originating from the triggering of the first tangential mode of the combustion chamber. Whereas the frequency of the first tangential mode is well defined by the square root dependence of adiabatic flame temperature, the magnitude of pressure fluctuations is observed to be intensified exponentially with increasing flame temperature up to 2200 K. We demonstrate that the transverse mode is characterized by high-amplitude spinning modes in the clockwise direction under relatively short combustor length conditions, discontinuously switching to counter-clockwise spinning modes at relatively long combustor length, and eventually transitioning to a moderate standing wave mode at the same resonant frequency. These observations demonstrate the previously unidentified complex modal dynamics induced by lean-premixed multislit hydrogen-air flames of nozzle dimension comparable to the characteristic length scale of the flame.

Bubble dynamics and pressure oscillation in highly subcooled water jet array impingement boiling under periodical heat flux

Jet array impingement boiling is promising to be used in the applications of large-area high-heat-flux cooling. In this study, the bubble dynamics and pressure oscillations of a one-dimensional confined jet array impingement boiling of highly subcooled water on smooth silicon wafer surface under periodical heat fluxes are investigated experimentally. It is found nucleate boiling mainly occurs nearby wall jet collision (WJC) zones and the initial bubble nucleation starts after a certain period of time in each heating cycle, which is insensitive to heating frequency under the present experimental conditions but related to the positions of WJC zones due to the crossflow effect. The initial bubbles have relatively larger size and will departure from heating surface or not, while the offspring bubbles have relatively smaller size and will not departure from heating wall but collapse on the heating wall. The collapsing of the above two kinds of normal-sized bubble will generate microbubbles (i.e., Microbubble emission boiling, MEB) and the number of microbubbles in jet chamber increases during the heating period. The periodical bubble growth and collapse causes high frequency pressure oscillation, with its frequencies being related to the bubble nucleation rates. The peak oscillation frequency shows somewhat increasing trend with the increasing of heating frequency.

Attenuated Chamber-Pressure Signal Reconstruction Using Maximum-Likelihood Estimation and Optimal Deconvolution

Chamber pressure, as it develops during rocket combustion, strongly correlates with many of the internal motor ballistic properties, including combustion stability, fuel regression rate, and mass flow. Chamber pressure is also an essential measurement for calculating achieved thrust coefficient and characteristic velocity. Because of the combustion environment hostility, sensing chamber pressure with high fidelity presents a difficult measurement problem, especially for solid and hybrid rocket systems, where combustion by-products contain high amounts of carbon and other sooty materials. These contaminants tend to deposit within the pneumatic tubing used to transmit pressure oscillations from the thrust chamber to the sensing transducer. Partially clogged transmission tubes exhibit significant response latency and damp high-frequency pressure oscillations that may be of interest to the testers. A maximum-likelihood method for fitting a second-order model to chamber-pressure response is presented. The resulting model is subsequently used to reconstruct a high-fidelity motor response via optimal deconvolution. The method is applied to small hybrid-thruster results from three separate testing campaigns. Key performance parameters, such as thrust coefficient, characteristic velocity, and specific impulse, are recalculated using the reconstructed data. Results are compared to the unreconstructed data and are shown to exhibit consistently better agreement with theoretical predictions.

Experimental research on the performance of a rotating detonation combustor with a turbine guide vane

Rotating detonation engines (RDEs) have received significant attention from industry and academia alike, owing to their numerous advantages, such as pressure gain combustion, high operation frequency, and near-constant thrust output. Furthermore, there is considerable interest in combining RDEs with gas-turbine engines to further improve their overall system performance. This study examines the propagation characteristics of continuous rotating detonation waves (CRDWs) with a turbine guide vane (TGV). We develop an experimental model of a hydrogen–air rotating detonation combustor integrated with a TGV section and record the high-frequency pressure oscillations and static pressure upstream and downstream of the TGV section. The experimental results indicate that: the interactions between CRDW and the turbine blade cause the reflected shock propagating backwards to the combustor. Both pressure oscillation amplitude and static pressure decline at downstream of TGV. Notably, the pressure oscillation attenuation by the TGV is influenced by the direction of CRDW propagation. When the CRDW propagation direction and the flow path direction of the guide vane are opposite to each other, the pressure oscillation attenuation increases. The findings obtained herein provide benchmark data that help improve the fundamental understanding of CRDW and TGV interaction, and can be used to develop detonation-based propulsion technology.

Experimental study of overpressure and temperature field behaviors of a methane-air mixture with different ignition positions, solid structure obstacles and initial turbulence levels

For gas explosion accidents occurring in buildings, the explosion characteristics may be affected by the presence of the equipment and furniture, and the temperature produced by the vented explosion threatens the safety of surrounding personal and buildings. To investigate the internal overpressure and external temperature behaviors, explosion venting tests of methane-air mixtures were conducted in a self-designed 4.5-m3 square chamber, by changing the solid obstacles, ignition positions, and initial turbulence levels. The results showed that P1 is generated due to the venting rate exceeding the volume growth rate of products after vent opening; with increasing flame propagation, flame front increases and more folds are present on the surface during venting, when the rate of combustion product exceeds the venting rate again, then P2 forms. Ignition position and obstacles have little effect on P1, but affect the Helmholtz oscillation and high-frequency pressure oscillation (P4). Front ignition leads to the longest duration of Helmholtz oscillation and central ignition results in the largest P4. In the presence of obstacles, P4 is eliminated and strengthened in the cases of rear and front ignitions, respectively. P4 decreases and then increases as a function of the number of obstacles. Front ignition leads to the lowest temperature peak, rear and central ignition results in the same temperature peak. The length of the high-temperature field is the shortest under four obstacles and front ignition, respectively. Under strong initial turbulence, the overpressure peak, length and duration of the high-temperature field are the largest.

Analysis of Diesel Knock for High-Altitude Heavy-Duty Engines Using Optical Rapid Compression Machines

In high altitude regions, affected by the low-pressure and low-temperature atmosphere, diesel knock is likely to be encountered in heavy-duty engines operating at low-speed and high-load conditions. Pressure oscillations during diesel knock are commonly captured by pressure transducers, while there is a lack of direct evidence and visualization images, such that its fundamental formation mechanism is still unclear. In this study, optical experiments on diesel knock with destructive pressure oscillations were investigated in an optical rapid compression machine. High-speed direct photography and simultaneous pressure acquisition were synchronically performed, and different injection pressures and ambient pressures were considered. The results show that for the given ambient temperature and pressure, diesel knock becomes prevalent at higher injection pressures where fuel spray impingement becomes enhanced. Higher ambient pressure can reduce the tendency to diesel knock under critical conditions. For the given injection pressure satisfying knocking combustion, knock intensity is decreased as ambient pressure is increased. Further analysis of visualization images shows diesel knock is closely associated with the prolonged ignition delay time due to diesel spray impingement. High-frequency pressure oscillation is caused by the propagation of supersonic reaction-front originating from the second-stage autoignition of mixture. In addition, the oscillation frequencies are obtained through the fast Fourier transform (FFT) analysis.

Experimental Investigation on the High-frequency Pressure Oscillation Characteristics of a Combustion Process in a DI Diesel Engine

It is difficult to decompose the in-cylinder pressure of combustion of the direct injection (DI) diesel engine, a transient process associated with complicated oscillation components, because of its steep property. An adaptive cyclic average method based on time varying filter based empirical mode decomposition (TVF-EMD) is proposed to decompose the in-cylinder pressure signal, and the cyclic number is determined adaptively with protruding ratio of high-frequency oscillation. The proposed method is used to compare with the ensemble empirical mode decomposition and original TVF-EMD. The results indicate that the proposed method can overcome the drawbacks of these methods and extract high-frequency oscillations accurately and effectively. Three evaluation indexes, center frequency, normalized energy, and average center frequency are defined to analyze the frequency and energy characteristics of high-frequency oscillation quantitatively. The influence of speed, load, rail pressure, main injection timing, pilot injection interval, and pilot injection quantity are investigated systematically. The energy of high-frequency oscillation reaches the peak at medium-high speed, and increase with engine load and rail pressure. However, the relationship of high-frequency oscillation with fuel injection parameters are non-monotonic.

Nonlinear controller design and testing for chatter suppression in an electric-pneumatic braking system with parametric variation

Abstract Accurate pressure control is essential for an electric-pneumatic braking system (EPBS). However, component wear and prolonged service can cause EPBS parameters to drift, which results in system chatter with high frequency. Such is a state of nonlinearity and instability that leads to the gradual deterioration of pressure control. Designing a viable controller for the system is challenging as it requires that system nonlinearity, sensor configuration, and computing capacity be considered. This article addresses the issue and presents a 2-step nonlinear control strategy. An LMS-based adaptive feedforward amplitude-phase regulator is first employed to reduce the frequency of the high frequency pressure oscillation to low frequency’s, followed by applying an output feedback controller based on high gain observer to mitigate the low frequency oscillations to realize steady state. A logic rule is designed to ensure that the two controllers work to suppress pressure oscillations of high and low frequencies in coordination. A comprehensive system model is derived to help characterize system nonlinearities and for designing the high gain observer. Numerical and physical validation are executed to demonstrate the feasibility of the strategy and for the performance of the controller design. Experiments results shows that the nonlinear controller can supress the chatter within 0.1 s either in step response or sinusoid tracking when system parameters vary.

Equivalence ratio variation and combustion instability in hybrid rocket

In this paper, a series of combustion tests using PMMA/O2 was conducted to examine the initiating characteristics of low frequency instability (LFI) in relation to the changes in both flow and combustion conditions. By selecting parameters such as the oxidizer mass flow rate, fuel grain length, and mixing ratio of mixture oxidizer composed of oxygen and nitrogen; combustion tests were conducted to vary the equivalence ratio in the combustion. This study further validated instability characteristics in connection with coupling behavior between the high frequency pressure and heat release oscillations in 500 Hz band. Based on the results, a combustion stability map was plotted and it shows that the initiation of LFI is contingent upon the satisfaction of specific conditions of flow and combustion. The results also confirmed that the initiation of LFI is highly linked to an establishment of a positive coupling between high frequency pressure and heat release oscillations. In addition, equivalence ratio was found to be a critical factor in the transition of coupling status between the two high frequency oscillations. For a given flow condition, the sole increase in equivalence ratio above a certain threshold resulted in the phase shift between the two oscillations leading to a positive coupling or vice versa.

Mathematical simulation of the motion law of differential mortar pump piston intended for construction mix

The paper is dedicated to the creation of a differential mortar pump with electromagnetic action for pumping finishingmaterial, which is not sensitive to electric energy gaps, and which is at the same time convenient, easy to use, reliable andeconomical in operation. The paper presents the mathematical model of the working process dynamics of a differentialmortar pump with electromagnetic action, which will allow to study common patterns of pumping processes in the pump inthe whole, to solve general problems on their calculation and design, to set and solve problems of reliability control,connected with high-frequency pressure oscillations, the problems of structural optimization and optimal design of all itselements. The control system of a pumping unit with vector controlled asynchronous electric drive is proposed on the basis ofthe concept of inverse dynamics problems in combination with the minimization of local functionality of instantaneousenergy magnitudes, which ensures high-quality pressure regulation under the conditions of parametric perturbations activityand has acceptable energy indices.

Vibration Characteristics of Compression Ignition Engines Fueled with Blended Petro-Diesel and Fischer-Tropsch Diesel Fuel from Coal Fuels

Fischer-Tropsch diesel fuel synthesized from coal (CFT) is an alternative fuel that gives excellent emission performance in compression ignition (CI) engines. In order to study the vibration characteristics, which are important for determining the applicability of the fuel, CFT-diesel blends were tested on a CI engine to acquire vibration signals from the engine head and block. Based on the FFT and continuous wavelet transformation (CWT) analysis, the influence of CFT on the vibration was studied. The results showed that the root mean square (RMS) values of the vibration signal decrease as the proportion of CFT in the blends increases. The CWT results indicated that the vibration energy areas motivated by the pressure shock of transient combustion were weak with increasing CFT proportion for the different frequency bands. The blend of 90% pure petro-diesel and 10% CFT registered the largest RMS value for piston side thrust response, and the RMS of high-frequency pressure oscillation response is greater than that of the main response of combustion, for FT30. Therefore, CFT has the potential to reduce the combustion vibration of the engine at all frequency bands, and there is a possibility that the proportion of blended fuel can be modified to satisfy the vibration characteristics requirements in different frequency bands.