The MALIN 6000 is the latest development from Malin Instruments Ltd, the manufacturers of the first commercial portable engine-analyser. The first MALIN was a stand-alone unit that did little more than show a pressure trace and provide basic calculations on a graphics screen, but the award-winning design was quickly adopted by a large number of customers world-wide. with the massive expansion of PC usage over the following years the MALIN family has gradually developed to depend on a computer for archiving and analysis of data. This increased data processing capability has greatly added to the usefulness of the equipment, but at the same time the demands of the users have grown significantly. There is currently a strong desire by users to have available other information to use in conjunction with the pressure data. The MALIN 6000 has been designed to address these added requirements whilst also keeping up with current trends in PC equipment. Eighteen years of experience together with feedback from a large customer base has allowed Malin Instruments to greatly simplify the user interface and incorporate a wealth of new features, whilst simultaneously reducing the cost of the basic system. The MALIN 6000 is designed to provide a basic tool at a relatively low cost but be easily expandable as requirements develop. The same basic piece of hardware will be used from the simplest to the most complex installation. This means that even the basic tool offers components and software of a high quality, with the result that the MALIN 6000 offers by far the best value for money in its field on the market. The basic unit consists of a completely redesigned analyser together with the proven MALIN pressure transducer and the TDC detector (Magnetic or Laser variants). The MALIN 6000 offers the following features : Rugged and ergonomic instrument design. Multi-engine collection capability, test all your engine in one go. Greatly increased storage; no need to setup the Malin again after the inital installtion as all information on engines is retained within the instruments non volatile flash memory for use on demand. To test an entire engine the operator has only to press one simple OK button when prompted. Superimposed vibration information on the pressure traces. Detect any engine event and accurately synchronise it with the pressure trace. Superimposed injection pressure profiles on the pressure traces. Malin AVS encoder wheel for precise timing on slow speed engines. Continuous mode to view continuously updating pressure traces on screen. Easy USB connectivity. No more USB/Serial converters and / or comms port numbers! All components designed and manufactured in England.
The MALIN 6000 records a pressure trace which is synchronised with the rotation of the engine. In practice the pressure is measured via the indicator cocks and the assumption made that this pressure is also that acting on the piston and hence the force acting instantaneously on the piston is known. In fact because of gas dynamics this assumption is not entirely true but is generally accepted and is used in the analysis of combustion via PV traces. If the engine were rotating at a constant angular velocity then all that would be necessary would be to record pressure at regular intervals of time and use the engine speed to deduce the corresponding crank angles. This approach is used on the Malin at speeds above 120rpm. Above this speed the engine speed is sufficiently constant to allow a single pick up point to give results of resonable accuracy. This is certainly not true for long stroke slow speed engines where there are very signifcant angular velocity variations throughout the cycle. It has been shown experimentally that the errors in this are less than 0.5 degrees above 120rpm but increase as engine speeds drop, leading to significant IMEP errors. The most commonly used method of determining the piston position is to use one or more magnetic pickups, one detecting TDC and the other to count the flywheel teeth. This method is not precise enough to give accurate results on long slow speed engines. A typical flywheel has around 100 teeth giving only 100 pulses per rev which corresponds to a 3.6 degree angular resolution. The MALIN 6000 uses an angular velocity sensor (AVS) for low speed engines which is essentially a rotary encoder giving up to 3600 pulses/rev (0.1 degree resolution) and driven by the shaft. This gives good results but even this cannot eliminate the effect of crankshaft wind-up under load. The need for accurate phasing is paramount for IMEP calculations but not so important for other practical diagnostic deductions that can be made from the resulting pressure traces. The starting point for the pressure recording is BDC for each cylinder. This point is calculated as a time (or number of AVS pulses) after TDC on cylinder 1 which is itself detected by means of a laser on reflective tape or hall-effect device. The required offset for each cylinder is calculated on the basis of the engine geometry by the PC during set-up and passed to the instrument. AVS sensor (angular velocity sensor) only for use on slow speed 2 stroke engines. The AVS sensor must be used in conjunction with either the magnetic or laser sensors. The Malin pressure transducer is designed to withstand the harsh conditions found in engine rooms, in particular the high temperatures and vibration at the indicator cock.
DRAW CARDS A draw-card, i.e. plot of Pressure v Crank Angle starting at BDC and extending for 360 degrees (2-stroke) or for 720 degress (4stroke). This will be the most familiar to engineers. The main features of this diagram, starting at BDC on the compression stroke, are as follows:a) An increase in the pressure due to compression. The rate and final value of the pressure rise in this phase are direct indications of the quality of the sealing of the cylinder and any deficiency in, say, piston rings should be evident from this phase. A reduced turbo performance will also effect this phase markedly. In some engines, notably large slow 2-strokes, the piston will go over TDC before combustion starts. In this case the value of Pcomp is close to the value of P at TDC and indeed this is the default value used by the MALIN. Under these circumstances or indeed with any engine when motored, the peak pressure due to compression will occur slightly before TDC (typically 0.5degrees, because of heat loss from the cylinder) and is a good check on the accuracy of your marker positions. Any deficiency here can be corrected in the MALIN set-up. In the case of faster engines the additional pressure rise due to combustion will start to occur before TDC thus masking the value of Pcomp. In this case there is the option of acquiring Pcomp by motoring the engine or choosing a value of crank angle a few degrees BTDC as your reference position. The MALIN software supports this latter option by allowing the editing of Pcomp and by providing a facilty to show the balance of the pressure at any angle. b) An increase in pressure due to combustion. At some point near TDC the injection will start and sometime later sufficient fuel will be burning to increase the pressure above that expected due to piston motion alone. This ignition delay (IDEL) will be followed by a rapidly increasing pressure as full combustion gets underway. In a diesel engine (unlike a spark ignition engine) the fuel is being delivered during combustion at a rate which is determined by the characteristics of the injector pump. A primary aim is to deliver fuel at a rate which allows smooth burning without excessive rates of pressure rise which would cause undue stresses on, and excitation of, the engine components. Monitoring the RPR (The Maximum Rate of Pressure Rise) and keeping the balance of RPR even will reduce stress and consequently reduce engine failure. RPR is shown on the data sumary. In some cases the maximum rate of pressure rise due to combustion can actually be less than that due to compression. An injector is designed to admit fuel only above a certain fuel pressure and a injector which does not do this will be injecting fuel outside the correct time interval, with clear effects on the draw card. During the ignition delay period only a certain amount of fuel must be injected or the inital rate of pressure will be too great. Burning will continue, thus trying to increase the cylinder pressure whilst the piston is going down this trying to reduce the pressure. At some point the competing effects will lead to the pressure reaching a maximum but injection will continue past this point. The difference between Pmax and Pcomp is presented as Pdiff (The maximum pressure increase due to combustion) and is useful as a indicator of cylinder performance. c) A reduction in pressure due to expansion. As the piston goes down and injection and thus combustion ends the pressure in the cylinder will be above that which would have occurred in a motored engine. It is this pressure increase that is giving the power output of the engine and the time for which this is significant will depend on the engine design. For example an ultra-long stroke slow speed engine will, by design, be generating significant amounts of power for most of the down stroke but this is not so for a high-speed generator. This is best observed on a PV diagram (see below). In this case the large pressures around TDC contribute little to work output (i,e, a large P does NOT mean a large Pdv) and thus it does NOT follow that because a cylinder is producing a reasonable Pmax it is contributing its share to the engine output. This is a very strong reason for not relying on a peak pressure meter for engine balancing. Only by monitoring the balance of Pmax, Exhaust temperatures and IMEP can the engine be balanced efficiently. With mechanical indicators it is not possible to view the data from all cylinders together. d) Gas exchange phase As the piston ends its stroke the details of the gas exchange process (e.g. valves opening) will be reflected in the cylinder pressure. This is best viewed on a weak spring diagram.
New Features VIBRATION ANALYSIS CONTINUOUS AND FREE RUNNING MODES Vibration information when synchronised with engine rotation can provide useful information about the mechanical condition of a unit at a relaively low cost. This is a qualitative measurement in the sense that a base line must be established but it can give a early indication of such common problems as broken piston rings. With the addition of Manual, Continuous and Free runing modes the engineer can now easily record data from just one cylinder, and can also see continuously updated draw cards and pressure values (Minimum, Maximum and average peaks) on the instrument screen. ADDITIONAL EQUIPMENT USB PC CONNECTIVITY In keeping with the trends in the PC industry, the Malin product range now offer USB connectivity for simplified set up and download. No more comms port numbers to worry about. The malin 6000 can accept and record an analogue signal from external third party equipment. For infomation on a particular requirement please feel free to contact Malin Instruments. TO ARRANGE A DEMONSTRATION PLEASE CALL YOUR LOCAL DEALER MALIN INSTRUMENTS LTD 9E SWAINS MILL CRANE MEAD WARE ENGLAND SG12 9PY TEL : +44 (0)1920 460269 FAX : +44 (0)1920 469600 EMAIL : sales@malin.co.uk WEBSITE : www.malin.co.uk April 2008
DERIVATIVE DIAGRAMS A derivative diagram, i.e. a plot of the rate of change of pressure with angle v crank angle. The derivative diagram shows the rates at which pressure is changing in the cylinder. Remember that this rate is with respect to angle not time, if dp/dt is of interest then you must use the engine speed. Rates of pressure need to be limited and should, if injection is progressing correctly, show a smooth characteristic. The derivative will reach a maximum (RPR) at an angle (APR) which may correspond to compression or combustion depending on the type of engine. A positive derivative indicates pressure increasing, a negative value that pressure is decreasing and in this case a zero value shows that Pmax has been reached. The deriviative contains no further information than the draw card but is simply an alternative view. PV DIAGRAMS A PV diagram, i.e. a plot of Pressure v Volume over 360 degrees (2-stroke) or 720 degrees (4-stroke). This volume V is the swept volume, i.e. take no account of the fixed volume in the cylinder. The swept volume is deduced from the crank angle and the engine bore, stroke and conrod length. This view is important because of the close relationship between PV diagrams and power output. A further feature in the MALIN software is that during compression the relationship PVn=const should apply where V in this equation is the total cylinder volume, and n is the socalled polytropic index and has a value typically of about 1.35. The point at which this relationship no longer applies is used to determine the ignition point to a better accuracy than can be obtained from study of the pressure alone. DATA OVERLAYS Data from several cylinders can be overlaid on the same graph. Overlaying cylinders immediatley shows any differences from one cylinder to another. Data can be overlaid historically allowing reference to baseline data or sea trial data. This gives the engineer the ability to compare the data he has taken today with the ideal cylinder data.
BALANCE DIAGRAMS All the measured, calculated and manually input data can be displayed in the form of bar charts. Data shown in this format is invaluable for maintaining the engine keeping mechanical and thermal stress as low as possible. The balance of the Pmax can be examined at any point throughout the cycle. Viewing the balance of Pmax before any fuel is injected will show whether all the cylinders are compressing properly or not. Viewing the balance well after top dead center will show any early or late opening valves. Checking on compression and valve performance now takes a few seconds. BASELINE DATA Baseline data for most parameters can be taken from the shop or sea trial data and stored in the software for comparison with the current data. Baseline data can be stored for the complete range of engine loads. When the current data is viewed against the baseline data for the same load setting then any discrepancies will be highlighted in red on the data summary, this indicates immediately that there is a problem. This feature of the Malin 6000 makes it very difficult for a potentially disastrous and expensive mistake to go unnoticed even by the most inexperienced engineer. TREND DIAGRAMS The facility to trend data is also available, and is extremely important if long term performance is to be monitored. The ability to trend data also allows the user to schedule engine maintenance more efficiently thus reducing down time due to unexpected failure of engine components. With careful trend monitoring maintenance periods can be extended resulting in more efficient use of engine parts.