Search Results

Understanding of the oil film formation mechanism around a piston skirt is very important to reduce the friction loss at piston skirt. We have investigated lubricant oil film behavior around piston skirt which is affected by piston slap under motoring condition. In this study, a cylinder liner of a commercial engine is displaced with a quartz cylinder. Photographic observations of oil film behavior between the cylinder liner and the piston skirt were performed with two kinds of methods; direct monochromatic photography and LIF (Laser Induced Fluorescence) image using a high speed camera. The oil film distributions were determined from oil boundary observed by the direct photography, and oil film thickness was estimated from the LIF intensity. Differences of the oil film distributions and the oil film thickness depending on piston shapes were investigated for four types of pistons.

In this study, in order to clarify the mechanism of preignition occurrence in highly boosted SI engine at low speed and high load operating conditions, directphotography of preignition events and light induced fluorescence imaging of lubricant oil droplets during preignition cycles were applied. An endoscope was attached to the cylinder head of the modified production engine. Preigntion events were captured using high-speed video camera through the endoscope. As a result, several types of preignition sources could be found. Preignition caused by glowing particles and deposit fragments could be observed by directphotography. Luminous flame was observed around the piston crevice area during the exhaust stroke of preignition cycles.

Investigation of knocking combustion in a hydrogen spark-ignition engine is one of the major challenges for future vehicle development. The knock phenomenon in a Spark-Ignition (SI) engine is caused by autoignition of the unburned gas ahead of the flame. The explosive combustion of the end-gas creates a pressure wave that leads to damage of the cylinder wall and the piston head of the engine. We observed autoignition in the end-gas region due to compression by the propagating flame front using a high-speed colour video camera through the optically accessible cylindrical quartz window on the top of the cylinder head. Moreover, a high-speed monochrome video camera operating at a speed of 250, 000 frame/s was used to measure the pressure wave propagation. The goal of this research was to improve our ability to describe the effect of the autoignition process on the end-gas and propagating pressure wave during knocking combustion with the help of a high-speed video camera.

A square-piston engine simulator used at Berkeley to study both spark-ignited and diesel engine processes is described. The square piston configuration provides optical access to fluid mechanical and combustion processes through two fiat quartz windows used as cylinder walls. Results from three previous research projects are reviewed to illustrate the engine's capabilities. Since these studies, we developed and used a color schlieren cinematography system to record in-cylinder processes. Color schlieren movies of both spark-ignition and diesel combustion reveal the essential fluid mechanical and combustion features within the engine. For these movies, we redesigned the diesel fuel system and installed a new liquid fuel injection system for spark-ignited operation. By preventing fuel and soot condensation on the windows, these new fuel systems improved the quality of our Schlieren images.

Pre-chamber combustion (PCC) has re-emerged in recent last years as a potential solution to help to decarbonize the transport sector with its improved engine efficiency as well as providing lower emissions. Research into the combustion process inside the pre-chamber is still a challenge due to the high pressure and temperatures, the geometrical restrictions, and the short combustion durations. Some fundamental studies in constant volume combustion chambers (CVCC) at low and medium working pressures have shown the complexity of the process and the influence of high pressures on the turbulence levels. In this study, the pre-chamber combustion process was investigated by combustion visualization in an optically-accessible pre-chamber under engine relevant conditions and linked with the jet emergence inside the main chamber. The pre-chamber geometry has a narrow-throat. The total nozzle area is distributed in two six-hole rows of nozzle holes.

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. In order to better understand oil transport, a laser induced fluorescence technique is used to visualize oil motion on the side of the rotor during engine operation. Oil transport from both metered oil and internal oil is observed. Starting from inside, oil accumulates in the rotor land during inward motion of the rotor created by its eccentric motion. Oil seals are then scraping the oil outward due to seal-housing clearance asymmetry between inward and outward motion. Cut-off seal does not provide an additional barrier to internal oil consumption. Internal oil then mixes with metered oil brought to the side of the rotor by gas leakage. Oil is finally pushed outward by centrifugal force, passes the side seals, and is thrown off in the combustion chamber.

Ethyl tertiary-butyl ether (ETBE), a reaction product of ethanol and isobutylene, has been proposed as a high-octane blending component for gasoline. Laboratory studies have been conducted to determine how the addition of ETBE to gasoline affects the volatility characteristics of the fuel, and how the effects of ETBE compare with those of the commonly used oxygenates, ethanol and MTBE. The amount of vapor generated in bench-scale simulated evaporative emissions tests with each of those three oxygenates was also determined. The vapor pressures of gasoline-ETBE blends decreased linearly as the concentration of ETBE was increased. In contrast, ethanol addition raises the vapor pressure of gasoline, although in a nonlinear fashion. ETBE increased the mid-range volatility of the fuel, in the same way as a pure hydrocarbon of similar vapor pressure and boiling point.

During several test programs involving evaporative emissions and driveability, the vapor pressures and distillation characteristics of a large number of gasoline-alcohol and gasoline-ether fuel blends were measured. The maximum increases in Reid vapor pressure (RVP) above that of the gasoline alone ranged from 1.0 kPa (0.2 psi) for tertiary-butyl alcohol to 23.4 kPa (3.1 psi) for methanol. As little as 0.25 percent methanol, ethanol, or Oxinol ™ 50 (a 1:1 mixture of methanol and gasoline-grade tertiary-butyl alcohol) produced measurable increases in RVP. Because of the nonlinear response of RVP to alcohol concentration, mixing a gasoline and a gasoline-alcohol blend of the same RVP can produce a fuel with a higher RVP. The vapor pressures of fifteen gasolines and gasoline-alcohol blends were measured at several vapor-to-liquid ratios (V/L), With an increase in V/L, the vapor pressures of the gasolines were reduced more than the vapor pressures of the blends.

Computational procedures are described for combining a simple multicomponent fuel volatility model with flammability data to facilitate the analyses of a wide variety of practical situations involving methanol/ gasoline blends. These include fire hazards, fuel droplet or film evaporation, ignition, combustion and engine cold starting. In addition to outlining the computational procedures, several examples are given to illustrate possible applications. In particular, gasoline and M85 are compared as to their respective flashpoints, flammability of fuel tank headspace vapours, and fuel droplet evaporation under cold ambient conditions.

In order to improve the volumetric efficiency of a crankcase-supercharged 4-stroke cycle engine in the high speed range, rotary disc valves were used at both the inlet and the outlet sides of the crankcase. The effects of the size of the opening and the phasing of the disc valves on volumetric efficiency were investigated and compared with a system using reed valves. It was found that a volumetric efficiency higher than 120 % could be obtained over a speed of 3000-6000 rpm, which was not possible by using the reed valve system. SUPERCHARGING SYSTEMS utilizing Roots type blowers and/or exhaust turbochargers have been used effectively for increasing the brake mean effective pressure of 4-stroke cycle engines. The authors built a prototype cranckcase-supercharged 4-stroke cycle engine, which used the underside of the piston as a supercharging pump, and confirmed the effectiveness of the concept by motoring and firing tests.

Port fuel injection - PFI - engines are widely available and the calibrations of fuel models are well defined. Modern flex-fuel engines are designed to work with different fuels and a mix of them. However, Brazil’s ethanol is composed of anhydrous Ethanol mixed with 8% distilled water, making it distinct in relation of composition. In a PFI, the fuel mass is mixed to the air mass before entering the combustion chamber in order to keep the mixture most uniform as possible. In this process, heat exchange and partial pressure variation are present and this may lead to volumetric efficiency modification. However, measurement errors may be introduced from the indirect measurement method if it does not considers water content and combustion efficiency to determine volumetric efficiency.

Stringent vehicle emissions limits, fuel economy and driveability requirements demand an accurate air-fuel ratio management system. A flex fuel (ethanol capable) engine system without an ethanol sensor requires a precisely tuned air fuel ratio control system. In flex fuel systems without an ethanol sensor, the ethanol content is estimated based on the closed loop adaptation values, therefore; it is important to have a very good open loop estimate of cylinder trapped air and consumed fuel since an error in either of these values will cause a shift in the closed loop adaptation values and ultimately, in the estimated fuel ethanol content. This paper analyzes the effect of volumetric efficiency and stoichiometric air-fuel ratio variation of OTTO port fuel injection (PFI) engines when operating on ethanol. Proposals for correction of these parameters are compared to experimental data.

In two research programs, Volvo has investigated high performance turbocharged versions based on the new 3-litre inline six-cylinder naturally aspirated engine. Power and torque targets were 180 kW and 385 Nm respectively, with a wide usable torque range. The MEP-(Methanol Environment Performance)-project was linked to alternative fuel studies and focused on methanol (M85) and Flexible Fuel Vehicle-(FFV)-development. With alternative fuels, it is important to investigate not only the emissions and fuel efficiency, but also the performance potential, in particular when used in turbocharged engines. The MEP-engine could be reduced to 2.5 litre displacement, due to the good specific performance with M85 fuel. Higher charge pressures could be used compared to gasoline. An M85 turbocharged high performance engine must be designed for higher peak combustion pressures.

Results of the application of numerical simulation of the Navier-Stokes equations to the flow field inside a model of an internal combustion engine are presented. The numerical method is a hybrid vortex-finite element scheme, which combines the flexibility of finite element methods in handling complicated boundary conditions of the field equation, and the capability of vortex methods to reveal large scale convective structures at high Reynolds numbers. Moreover, it extends the application of vortex methods to compressible flows at low Mach number. At this stage, interest lies in predicting the flow structure within the cylinder during the intake and compression strokes. The effects of the piston geometry and the shape of the intake valve on the flow pattern are investigated. Qualitative comparisons with experimental data are discussed.

Decision that the fixed radial air-cooled type of aeronautic engine offers the most possibilities in light weight and maximum dependability was arrived at by the company with which the author is connected after a careful and comprehensive engineering analysis of many types of both water-cooled and air-cooled engine and therefore it undertook the development of this type. Because the Navy was desirous of obtaining a 400-hp. direct-drive engine and a 500-hp. engine to drive either direct or geared and because a commercial air-cooled engine to replace the Liberty-12 water-cooled engine was desirable owing to the increased pay-load it would make possible, it was decided to undertake first the development of a 400-hp. engine of this type. Work on the design was started Aug. 1, 1925, and the first engine was finished on Dec. 24, or approximately 5 months later. This engine was named the Wasp.

Wall quenching plays a vital role on particulate formation. A single cylinder engine test has been carried out to clarify the effects of wall quenching on particulate emission. A completely warmed up engine is fired in variety of operating period under various engine load, and then stopped immediately. Deposits are collected from 25 positions on the combustion chamber wall. Area basis concentration of deposit is obtained at each position. Soluble organic fractions (SOF) extracted from deposit are analyzed with gel permeation chromatograph (GPC). Results show the correlation between SOF in exhaust particulate and in deposit. Deposit concentration is highest on the spray axis impinging region of piston cavity wall. GPC pattern of the SOF in deposit indicates that higher molecular weight composition generates as a result of polymerization of fuel where the main jet region of the spray impinges.

The real cycle simulation is an important tool to predict the engine efficiency. To evaluate Extended Expansion SI-engines with a multi-link cranktrain, the challenge is to consider all concept specific effects as best as possible by using appropriate submodels. Due to the multi-link cranktrain, the choice of a suitable heat transfer model is of great importance since the cranktrain kinematics is changed. Therefore, the usage of the mean piston speed to calculate a heat-transfer-related velocity for heat transfer equations is not sufficient. The heat transfer equation according to Bargende combines for its calculation the actual piston speed with a simplified k-ε model. In this paper it is assessed, whether the Bargende model is valid for Extended Expansion engines. Therefore a single-cylinder engine is equipped with fast-response surface-thermocouples in the cylinder head. The surface heat flux is calculated by solving the unsteady heat conduction equation.

A simple imaging technique was explored as a means for characterizing in-cylinder wall wetting in GDI engines. For technique development, a GDI fuel injector was directed vertically down on the top of a temperature controlled flat piston within a non-motored research cylinder in an experimental arrangement described previously [3, 4, 6, 7, 14]. A three-factor randomized factorial design of experiments was performed that included laser sheet level (with three treatments including 0 mm, 2 mm, and 5 mm from the piston surface), piston surface temperature (with three treatments including 100 °C, 150 °C, and 200 °C), and time after start of fuel (with five treatments including 1 ms, 2 ms, 3 ms, 4 ms, and 5 ms after start of fuel). The technique for characterizing wall-wetting differences involved subtracting the 8-bit pixel intensity values at every pixel location for one laser-illuminated scattered image from another image.

This paper presents a new ethanol content identification concept, with focus on flex fuel vehicles start ability robustness. The solution refers to the usage of cold start system based on heated fuel rail (normally used for low temperatures) in a preventive way like an ethanol sensor, ensuring a successful start attempt in specific conditions, even at high ambient temperatures. At most of flex fuel projects, the ethanol content calculation (or the percentage of ethanol in fuel) is done through the oxygen sensor (also called lambda sensor). Therefore the engine start strategy considers the fuel mixture determined in the previous vehicle operation. In situations when the adaptation cycle is not completed during the operation cycle previous to the start attempt, and also in combination with an extreme fuel exchange situation after tanking (previous to the last vehicle operation cycle), it may happens that the first start attempt is not successful.