Preheat Time Research Articles

Model Experimental Study on De-Icing Method of Bridge Pylon Beam Based on Electric Heating

The icing of bridge pylon crossbeams is a problem that could pose a serious threat to traffic during a cold winter. However, little research has been carried out on the problem and few corresponding countermeasures have been provided. This paper aims to propose a novel heating system, and to study the feasibility of beam de-icing and the related de-icing strategies so as to provide a reference scheme for the practical application of beam de-icing. A number of icing and de-icing tests were carried out on a scale model of Wuhan Yangtze River Second Bridge in the cold chamber. The de-icing effects of the beam in different environments and different de-icing methods were compared, and the recommended pre-heating time, applicable environment range, and heating method were given. The results of the model experiments show that pre-heating the heating system can prevent the surface of the beam from freezing and that the anti-icing method is more suitable for beam de-icing than the passive de-icing method. When the pre-heating time exceeds 7 min, the entire anti-icing process can be ice-free. When the wind velocity exceeds 5 m/s, it is safer to shut down the heating system, and using the passive de-icing method at the end of the icing can also eliminate the hidden danger of beam icing.

PENGARUH PRE-HEATING PADA PIROLISIS BIOMASSA LIMBAH AREN TERHADAP CHAR PADA REAKTOR HORIZONTAL MODEL CONTINUOUS

<p><em>Utilization of palm waste in the form of charcoal briquettes makes the fuel more efficient and in a better form. Thus, charcoal briquette fuel with sugar palm waste is a solution or alternative to solving the waste problem caused by palm trees. This research was conducted with the aim of knowing the effect of pre-heating on the pyrolysis process of palm sugar waste biomass on gas fraction, bio-oil and char. This study used an experimental method conducted in the Mechanical Engineering Education Laboratory of Sebelas Maret University. The research variable is the variation of pre-heating time in the pyrolysis of palm waste biomass against gas fraction, bio-oil and char in a continuous model horizontal reactor. The result of this study is that pre-heating has an effect on the gas fraction. The longer the pre-heating process is carried out, the lower the amount of O2 gas produced. Pre-heating affects the char, so the quality and quantity can be measured.</em><em></em></p>

Optimasi unjuk kerja pada sistem pendinginan adsorpsi dengan siklus pemanasan-ulang kombinasi

The adsorption refrigeration system is a cooling system that offers several benefits, including being environmentally friendly due to the very small amount of global warming effect given, the lack of potential for ozone depletion, the low energy consumption of its operation, the low heat source used in its operation and good for reducing gas emissions on earth. This paper describes a combined reheating adsorption refrigeration system with three heat exchangers, as well as operating modes. The operation of the adsorption refrigeration system with combined reheating is schematically described with operational modes and diagrams. This adsorption cooling system is made up of three heat exchangers (H), one evaporator, and one condenser. The combination cycle is intended for heat exchanger systems that operate in a reheat cycle (H1 and H2) and a non-reheating cycle (H3). This paper also discusses system cycle time optimization. Research to get the optimum value of cycle time in this system is still rarely done and therefore optimization of cycle time is carried out on the system to get the best performance. The PSO (particle swarm optimization) program is paired with the MATLAB program to simulate the performance of the system under discussion while also enhancing its performance. The goal of this work is to use simulation to determine the optimal system performance versus the overall cycle time, which includes adsorption/desorption time, pre-cooling and pre-heating time as well as mass recovery time. Getting the best value for the entire cycle time is made possible by fusing the simulation of the system's process performance with performance optimization. As a results, the greatest increase in the optimization results' performance value occurs at a heat source temperature of 55ºC with a longer time to achieve optimal performance.

Polymerization and shrinkage kinetics and fracture toughness of bulk-fill resin-composites.

To determine degree of conversion (DC), maximum polymerization rate (RPmax), polymerization shrinkage (PS), maximum shrinkage rate (PS Rmax) and fracture toughness (KIC) of different types of bulk-fill (BF) composites plus the effect of viscosity reduction techniques. BF specimens were created in 2 mm deep molds: SonicFill 3 (SF3), Viscalor (VC), One Bulk Fill (OBF) and Beautifil Bulk (BBR). SF3 was applied via sonic insertion using a SonicFill handpiece (Kerr Corp. USA). Viscalor was pre-heated in a Caps Warmer in T3 mode (at 68 °C) for 30 s (T3-30 s) and 3 min (T3-3 min), respectively. Specimens were irradiated at zero distance from the upper surface with an Elipar S10 LED unit (3 M ESPE, USA) of mean irradiance 1200 mW/cm2 for 40 s. Real-time polymerization kinetics and DC at 5 min and 24 h post-irradiation (DC5 min and DC24 h) were measured using ATR-FTIR (n = 3). PS was measured up to 1 h on 1 mm thick discs via the bonded-disk technique (n = 3) and PS Rmax obtained by numerical differentiation (n = 3). For fracture toughness, single-edge-notched specimens (32 × 6 ×3 mm) of each BF composite were prepared and measured by three-point bending after 7 d water storage (n = 5). Data were analysed using One-way ANOVA, independent T-tests and Tukey post-hoc tests (p < 0.05). SF3 showed the significantly highest DC5 min, DC24 h and RPmax (p < 0.05), followed by OBF (p < 0.05). Regardless of pre-heating, VC showed comparable conversion kinetics to BBR (p > 0.05). There was no significant difference in PS of these BF composites, except OBF had the highest PS (p > 0.05). However, PS Rmax significantly varied among materials (p = 0.047) and SF3 had the highest PS Rmax. Regarding fracture toughness, BBR had the lowest KIC (p < 0.05), whereas other composites showed similar KIC (p > 0.05). Strong correlations of filler content (wt%)-PS/KIC were found. Different pre-heating times had no significant influences on DC %, RPmax, PS, PS Rmax and KIC of VC (p > 0.05). Different types of bulk-fill composites showed comparable shrinkage. A highly filled BF giomer composite (BBR) had the lowest fracture toughness, whereas others had similar KIC. Pre-heating had no adverse effects on Viscalor properties. Sonication and pre-heating are beneficial techniques to enhance composite flowability without either increasing shrinkage or reducing fracture toughness.

Preheating time estimation in intermittent heating with hot-water radiators by considering model uncertainties

Intermittent heating refers to heating buildings only during occupied periods. Owing to the thermal inertia of buildings, a preheating time is necessary to bring the indoor temperature into a comfortable range at the start of occupied periods. This paper proposes a new method to estimate the preheating time in intermittent heating with hot-water radiators by considering model uncertainties. First, a dynamic physical model is established based on the thermal equilibrium of buildings, and is approximated as a first-order continuous-time model by ignoring the influence of ambient conditions on the indoor temperature. The ignored part is represented as model uncertainties. Second, the continuous-time model is identified from collected data of indoor temperature and supply water temperature, and the model uncertainty is obtained based on the identified model. Third, the preheating time is determined with a credible probability to ensure that the indoor temperature meet thermal comfortable requirements. The proposed method has two novel features: (i) it can be applied to buildings with unknown physical parameters and unmeasurable ambient conditions, and (ii) it can yield reliable estimates of preheating time based on the model uncertainties to ensure the success of preheating under a given probability. Experimental examples demonstrate the effectiveness of the proposed method.

Optimasi waktu pemanasan awal dan waktu pasteurisasi PEF terhadap asam lemak bebas, vitamin C, dan pH pada pengolahan susu

RSM (Response Surface Methodology) is one method that is widely used for process optimization. The purpose of this study was to obtain the optimum combination of treatments in milk processing. The combination of treatments given was pre-heating time and pulsed electric field time with response levels of free fatty acids (%), vitamin C (mg/ml), and pH. The pre-heating temperature used was 70ºC and the voltage of pulsed electric field was 15 kV/cm. Software Design Expert 13 was used to optimize the milk processing. The optimum condition obtained was a combination of heating time treatment for 5 minutes and pulsed electric field time of 135.608 seconds. The combination of these treatments resulted in a response of free fatty acids levels of 0.002%, vitamin C of 0.217 mg/ml, and pH value of 7.087. The desirability results or results accuracy of the optimum solution show a value of 0.441. The PEF utilization as a low-temperature milk processing can improve milk quality. Optimization of the use initial temperature in combination with PEF is usefull for the effectiveness of milk processing

Time-Temperature Profiles Effect on Thermoluminescence Glow Curve Formation of Germanium Doped Optical Fibres

The development of optical fibres technology grows in response to seeking a radiation detector with better thermoluminescence (TL) performance. Concerning the dosimetric characterization study by previous researchers, this research work has widened the exploration to optimize the time-temperature profile (TTP) in connection with the glow curve formation of the optical fibres. Two forms of germanium (Ge) doped optical fibres, namely cylindrical optical fibre (CF) and flat optical fibre (FF) were fabricated, and the TTP were investigated prior to commissioning the optical fibres for fieldwork. CF and FF were irradiated to the dose of 2 Gy using a 6 MV linear accelerator. Various TTP profiles, including preheat temperature, preheat time, acquisition temperature rate, and acquisition time were varied to determine the best thermal profile for the CF and FF based on the glow curve formations. Out of 4 parameters, an increase in preheat temperatures ranging from 40 to 120 °C caused a significant variation in the glow curve formation, thus possibly giving rise to different TL signals of the optical fibres. The maximum glow peak temperature of CF and FF was unvarying when different preheat temperatures employed. These findings support the conceptual idea that manipulating the optical fibres’ readout system can alter the glow curve formation. Thus, an optimized TTP will provide the correct glow curve configuration for kinetic parameter analysis.

Contact angle analysis and intermetallic compounds formation between solders and substrates under formic acid atmosphere

In 3D packaging, an increase in the solder bump density and reductions in solder-bump height are the roadblocks to using gel or liquid fluxes for the soldering process. Fluxless soldering has become a popular technology, and the formic acid (FA) atmosphere soldering is one of the most promising fluxless soldering techniques. In this study, the effects of FA atmosphere on contact angle and the intermetallic compounds formation between three different solders (Sn-58Bi, Sn-3.0Ag-0.5Cu, and Sn-0.5Sb) and two different substrates (Cu and Ni/Cu) were investigated. The results indicate that the wettability of those soldering systems of FA soldering is very similar to that of soldering with the solder flux. Moreover, the effect of pre-heat treatment on the wettability of the Sn-3.0Ag-0.5Cu solder (SAC)/Cu by FA soldering was investigated. With the increase in the pre-heat time, the soldering wettability was improved. And there was no significant difference in the interfacial reactions of SAC/Cu between FA and flux soldering according to the microstructural study results before and thermal aging. This paper verifies that the FA atmosphere is suitable for various lead-free solders and substrates to achieve fluxless soldering and then provides a theoretical reference for the industrialization of formic acid atmosphere in electronic packaging.

Effect of preheat & post-weld heat treatment on the microstructure and mechanical properties of 6061-T6 aluminum alloy welded sheets

MIG welding is one of the most predominantly welding techniques in manufactories due to its high automation. However, aluminum alloy welded joints fabricated using MIG welding often exhibit a reduction in mechanical properties. In this paper, an attempt has been made to combine preheat and post-weld aging treatment in double-pulse MIG (DP-MIG) welding process to produce 6061-T6 aluminum alloy welded sheets with high mechanical properties. Response surface methodology (RSM) was used to study the main effect and interactive effect of heat treatment parameters including preheat temperature, aging temperature and time on mechanical properties. On this basis, the optimum heat treat parameters that maximize both strength and ductility of welded joints have been determined using multi-objective optimization algorithm. Additionally, the influence of heat treatment parameters on the microstructural evolution and mechanical properties of welded joints was further investigated, by systematic experimental and theoretical analysis. The results showed the preheat temperature affects the grain size and precipitation of the welded joint, while the aging heat treatment mainly affects the precipitation and transformation of the strengthen phase. Since the aging temperature is of greater significance for the improvement of mechanical properties of welded joints, compared with other heat treatment parameters and their interactions, indicating the strengthening of precipitates determines the mechanical properties of welded joints.

Disc Forming by Friction Stir Consolidation of AA2024 Chips

This work aims to form a disc by recycling AA2024 chips using friction stir consolidation (FSC) technique. Initially, the chips were compacted inside a chamber by an applied pressure of 20.7 MPa. Different chips weights and two process parameters were studied in the FSC process: pre-heating time and plunging depth of the tool. The process was carried out at 1400 RPM. Effect of the process parameters and chips weight on chips quality was analyzed by design of the experiments method. The discs formed with a fully consolidated (FC) volume fraction range of 14.5-22.4%. The plunging depth was the most effective factor on surface finishing and grain size of the discs, while the chips weight was the most effective factor on the FC volume. Increasing the chips weight and plunging depth increased the FC volume. The average grain size of the disks ranged between 6.3 to 11 mm.

Microstructural evolution and mechanical properties of eutectoid Ti–7Ni alloy produced by electron beam powder bed fusion

A eutectoid Ti–7Ni (wt.%) alloy was additively manufactured by electron beam powder bed fusion (E-PBF) in this work. The effects of electron beam current and preheating time on the microstructure and mechanical properties of the E-PBF-built Ti–7Ni (wt.%) alloy were investigated. The evolution of the eutectoid microstructure during the in-situ heat treatment of E-PBF was elucidated. The addition of nickel resulted in a microstructure consisting of pre-eutectoid α laths and lamellae of submicron α and Ti2Ni. The morphology of the Ti2Ni evolved from fine lamellae to discontinued ellipsoids with increasing electron energy density or preheating time. Defects such as pores and lack of fusion were observed in the alloy under insufficient electron energy density. Fine Ti2Ni lamellae and pre-eutectoid α laths were obtained in the alloy processed at an electron energy density of 54 J/mm³ and a preheating time of 6 s, contributing to a considerable ultimate tensile strength of 660 MPa and good elongation of 16.8%. In addition, a graded microstructure along the building direction was observed due to the coarsening of Ti2Ni during multiple thermal cycles. It was demonstrated that the microstructure of the eutectoid Ti–7Ni alloy can be controlled by the in-situ heat treatment during the layer-by-layer E-PBF process. The findings in this work provide understanding and guidance for microstructure regulation in other additively manufactured eutectoid titanium alloys.

Friction Spot Lap Joining of Aluminum Alloy AA6061 to Pre-Holed and Threaded Carbon Steel AISI 1006

This work addresses to joining aluminum alloy AA6061 to carbon steel AISI 1006 sheets using the friction spot joining technique. The steel sheets were pre-holed and threaded with an internal M6 thread. The joining process was carried out by extruding the aluminum through the steel hole and thread using a rotating tool with friction between the tool and aluminum. Three process parameters were used: pre-heating time, rotating speed and plunging depth of the tool, with four levels for each parameter. The results indicated that the two materials joined by a micro-scale mechanical interlock at an interface line of a width ranged between &lt;i&gt;0.7&lt;/i&gt; to ~ &lt;i&gt;2.5 mm&lt;/i&gt;. The joint’s shear force reached a minimum and maximum value of &lt;i&gt;2000&lt;/i&gt; and &lt;i&gt;2500 N&lt;/i&gt;, respectively. The plunging depth was the most effective factor affecting the amount of the extruded aluminum and the joint’s shear force.

Preparation of municipal solid waste incineration fly ash-based ceramsite and its mechanisms of heavy metal immobilization

With an increase in municipal solid waste incineration (MSWI) fly ash and its dangerous characteristics, the manner of its disposal has caused widespread concerns. In this study, ceramsite was prepared by using MSWI fly ash, civil sludge, and contaminated soil as the main raw materials; then, a certain proportion of clay was added as an additive. The optimum MSWI fly ash content and sintering conditions were investigated, and the immobilization mechanisms of heavy metals were explored. Based on the obtained results, the optimum preparation conditions were a preheating temperature of 400 °C, a preheating time of 10 min, a sintering temperature of 1150 °C, and a sintering time of 20 min. Moreover, the optimal raw material ratio of MSWI fly ash, civil sludge, contaminated soil, and flint clay was 30%:40%:15%:15%. Under these optimum preparation conditions, the obtained ceramsite showed the following excellent performance parameters: a 1-h water absorption of 0.97%, bulk density of 998.7 kg/m3, and cylindrical compressive strength of 37.84 MPa. Furthermore, the leaching of heavy metals was far less than the standard GB5085.3-2007. The immobilization of heavy metals in the ceramsite was mainly caused by the glass phase encapsulation and the formation of new crystal phase with the heavy metals. In addition, the generation of aluminosilicates played a positive role in the immobilization of heavy metals. Thus, the reuse of MSWI fly ash by preparing fly ash-based ceramsite is one of the effective methods for reducing solid wastes.

Friction Spot Joining of AA6061 to Pre-holed Pure Copper Sheets with a Snap Rivet Head Die

This work aims to join AA6061 to Copper sheets using friction spot joining technique without formation of intermetallic compounds (IMCs). Aluminium (Al) sheets were arranged with a lap joint configuration over a pre-holed copper sheet. A snap die was used under the copper specimen. A rotating tool was utilized to carry out the joining technique by friction at the common surface between the tool shoulder and Al surface. Three process parameters were selected to study its influence on the joint quality: rotating speed, pre-heating time, and plunging depth of the tool. Two materials were joined by extruding the Al metal through the copper hole, and forming a rivet head. The results indicated the two materials joined by mechanical interlock at an interface line of a micro-scale, without forming IMCs or presence of defects like cracks, voids or gaps. The extruded aluminium through the rivet head die prevented pull-outing the joint. The plunging depth of the tool exhibited the highest influence on the joint’s shear force which recorded a maximum value of 1800N.

Experimental analysis on the bonding conditions of thermoset-thermoplastic composite parts manufactured by the hybrid single shot method

The hybrid single shot method is an innovative manufacturing technique that allows thermoset composite sheets to be formed and cured while they are also bonded into an injected thermoplastic body all in a single integrated operation. This integration concept is complex in nature but promising to overcome the drawbacks of the traditional procedures for manufacturing such multi-material structures by reducing the cycle time, energy consumption, and cost of the required tools and machinery. In this study, CF/Epoxy prepreg sheets are selected as the inserted material which is then later deformed and bonded to an injected body made of a polypropylene compound. The bonding between these two dissimilar materials is mostly achieved by taking the advantages of the melt penetration and the tackiness of the prepreg sheet. Therefore, an experimental study is here designed and carried out to evaluate the bonding conditions of the final hybrid parts regarding several influential process parameters. To better monitor the process and analyze the physics behind this integration, a set of real-time process variables are measured and analyzed using an instrumented experimental setup. The results show that the pre-heating time has the largest effect on the bonding strength, and the best combination of the deformation and bonding strength is achieved when the cavity pressure and temperature are at the highest level compared to the other experiments. The maximum bonding strength attained in the optimum process settings was 6.8 MPa which shows a 51% improvement compared to the average value of the other experiments.

Effect of Humic Acid Binder on Oxidation Roasting of Vanadium–Titanium Magnetite Pellets via Straight-Grate Process

The oxidation roasting of vanadium–titanium magnetite (VTM) pellets with a new composite binder was investigated using a pilot-scale straight-grate. The evolution of the chemical and phase composition, the compressive strength, and the metallurgical properties of the fired VTM pellets were investigated. Under a preheating temperature of 950 ∘C, a preheating time of 18 min, a firing temperature of 1300 ∘C, and a firing time of 10 min, the compressive strength of the fired pellets was as high as 2344 N per pellet. The fired pellets mainly consisted of hematite, pseudobrookite, spinel and olivine. The total iron content of the fired pellets was 0.97% higher using 0.75 wt% humic acid (HA) binder instead of 1.5 wt% bentonite binder. These properties are beneficial for the production efficiency and energy efficiency of their subsequent use in blast furnaces. Moreover, both the softening interval and the softening melting interval of the HA binder pellets were narrower than those of the bentonite binder pellets, conducive to the smooth and successful smelting of the VTM pellets in a blast furnace.

Joining of Aluminium Alloy (AA6061-T6) to Pre-Threaded Pure Copper by Friction Spot Lap joining (FSpLJ) Process

Objective - The objective of this study is to join Aluminum alloy type (AA6061-T6) of (1.5) mm thickness to pre-threaded pure copper of (2) mm thickness applying the frictional spot lap joining (FSpLJ) technique. Styling - All specimen aluminium and copper was prepared by cutting them by dimensions (100×25) mm, pure copper samples (2) mm thickness were pre-punctured with a diameter of (4) mm and then threaded it with a diameter of (4.8) mm, a tooth step (1) mm, a rotational instrument with a (10) mm diameter was used for the joining operation. Configuration - The threaded copper was put in the mold channel, placing aluminum on top of the copper, putting the fastener over the sample, and placing the top cover of the template and fixation it with three bolts. Approach - The process parameters [rotating speed (RPM), plunging depth (mm), and pre-heating time (sec.)] was optimized by using Taguchi style, there were four levels for each parameter. The influence of the operation parameters on the joint shear strength was analyzed. The tests [Visual examination, shear force, macrostructure, and the microstructure of the joint were applied]. Results – AA6061 was extruded through the pure copper hole and its interlock with the thread slot. As a result, it was obtained mechanical overlap between the extruded aluminum and the copper. The plunging depth parameter had the greatest influence on the shear strength of the joint. Increasing the plunging depth and the rotational speed of the tool was gradually increased the efficiency of the joint. The results showed that the samples failed to test shear in the zone of the lap joint. The highest shear force is (2176) N.

Friction Spot Joining (FSpJ) process of Aluminium AA6061-T6/Poly Vinly Chloride (PVC)

The goal of this research is to use a Friction Spot Joining (FSpJ) is a new technique which used for joining hybrid structures of metal-polymer composite. The FSpJ was proposed to join sheets of aluminum alloy of type AA6061-T6 and polymer of type polyvinyl chloride (PVC). The aluminum alloys sheets were of 3mm thickness, while the polymer sheets were of 5mm thickness. All sheets were manufactured with dimensions of 25*100 mm2. The aluminum sheets were drilled with two holes: the first of 8mm diameter with 1mm depth, the second hole was of the same pervious hole center with a penetrating hole diameter of d mm (2,4 and 6) the aluminum holes were made at a the center of the lap joint area. The process parameters included the rotating speed of the tool of 710, 900, 1120, 1400 and 1800 RPM, plunging depth of the tool of 0.1, 0.2, 0.3, 0.4 and 0.5 mm and pre-heating time of 5, 10, 15, 20 and 25 sec. The results indicated that all the specimens were joined successfully. The tested sample indicated that the failure of FSpJ joints occurred at two locations; the first at polymer side and the second was occurred by shearing the lap joint of specimens. The first type of failure indicated that the shear strength of the joined samples exceeded the shear strength of the polymer with a shear strength joint efficiency of more than 100%. The specimens that failed by shearing the polymer at the lap joint region were failed without dislocation the molten polymer from the aluminum hole cup. The shear force of the AL-PVC joints ranged from (704-1664N). The hole diameter exhibited the highest effect on the joint shear force followed by the plunging depth, rotating speed and pre-heating time of the rotating tool. The macrostructure examination and SEM tests indicate that a macro mechanical interlocking formed between the metal and filled hole which attributed to the main joining mechanism at the common surface.

Research on Energy Consumption Prediction Based on Machine Learning

Energy conservation and emission reduction is an important part of enterprise management. Energy costs directly affect the economic benefits of enterprises. Energy control of industrial air conditioning has long been the focus of the attention of enterprises. At present, enterprises often adopt fixed pre-cooling and pre-heating time for air conditioning start-up strategy, and there is no unified and scientific standard. By collecting and cleaning the historical data (climate, capacity) of air conditioning operation of enterprises, this paper establishes a scientific model of air conditioning energy consumption and a prediction model of air conditioning starting time. In addition, the theory and technology proposed in this paper are applied in practice to design and implement the air-conditioning energy control system of smart factory, and to predict the starting time of the air-conditioning in the production workshop of enterprises. The results show that the system can help enterprises achieve the goal of intelligent energy management and control.

Cooling system based on double-ball motor control valve

To realize eco-models based on (where 3R represents reducing, reusing, and recycling), both researchers and automobile development departments use controllable components to reduce vehicle fuel consumption and emissions. In this context, this paper presents the design of a double-ball motor control valve (DB-MCV). When compared with use of a traditional thermostat, use of the proposed valve in a Worldwide Harmonized Light Vehicles Test Cycle (WLTC) allows the coolant temperature to be controlled accurately as per the vehicle operating conditions, with control accuracy of ±1°C. Using this approach, the engine pre-heating time is reduced by 61 s, the total hydrocarbon (THC)) emission is reduced by 6.79%, the CO emission is reduced by 7.18%, and NOX emission is reduced by 4.84%. Under the same vehicle and working conditions, the engine fuel consumption is reduced by 2.31% on average. Under the cabin heating condition, the cabin temperature can be increased by 4.3°C, which improves the thermal comfort of the driver. When the vehicle is stopped after running at high speed and the engine is idling, the coolant temperature in the engine decreases rapidly, which reduces the risk of a hot dip occurring in the engine.