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MARPRIME SYSTEM – THE ALL-IN-ONE SOLUTION
OF CYLINDER PRESSURE HANDHELD DEVICES

The MarPrime System is a simple, user-friendly device for measuring cylinder pressure. It is designed to measure and analyze the combustion process of 2- and 4-stroke marine diesel engines and stationary power plants. This easy-to-use system offers the potential to gauge all the engines in your machine room and draw up well-founded diagnostic reports quickly with a high degree of accuracy.

It uses a high performance electric pressure transducer of well proven design allowing the cylinder pressure to be measured very accurately. With the MarPrime handheld device you have a “one-hand/ one-person” tool which quickly and easily collects and records the full range of engine performance data. Fast data transfer via network or USB connection and an automatic detection of the device guarantee an easy operation when reading out and displaying data. Using the supplied software the measured pressure sequences can be displayed accurately as a function of the crank angle.

MarPrime Instruct, MarPrime Ultra & Basic Software

Together with the new MarPrime Instruct and MarPrime Ultra, a single unit is now able to offer you full assessment of your engines in one hand: The MarPrime System. MarPrime Instruct determines the performance of your engine and enables you to compare it with other parameters.

A feature of the MarPrime Ultra version is the ultrasonic sensor. It enables the engine timing – such as the start and finish of the injection process and the engine valve timing – to be determined very precisely. In combination with our indication device MarPrime Ultra, the software MarPrime Instruct makes any other additional software obsolete.

Nevertheless, the included, basic software of the MarPrime System requires no additional installation of pick-up sensors or crankshaft position transmitters and will carry out the TDC correction of the pressure sequences automatically. Learn more about the MarPrime system:

  • Handheld device
  • Optimizing the engine operation
  • Monitoring the load balance
  • Checking the valve timings
  • Reducing fuel consumption and emissions
  • Determining condition of the cylinder head assembly
  • Reducing costs of replacement parts and maintenance 
  • No need of any pick-up sensor or encoder
  • Dynamical TDC calculation
  • Accurate power calculation
  • High accurate cylinder pressure sensor
  • Easy handling
  • Measuring at every engine
  • Self-explanatory evaluation software
  • With USB and network connector
  • Engine Diagnostic Far Beyond Cylinder Pressure
  • with dynamic TDC correction
  • no additional installation of pick-up sensors or crankshaft position transmitters is required

Additional Ultra Sonic Diagnostic

  • Determine Injection Timing
  • Determine Valve Timing
  • Determine Valve Leakages
System requirements for engine diagnosis

The standard engine diagnosis systems for main or auxiliary engines are based on recording the in-cylinder pressure. However, the combustion process should also be seen as a function of gas exchange and fuel injection. The combination of mobile cylinder pressure measuring devices with additional ultrasound measurement technology is a very promising approach to meeting both the current requirements for optimising the operation of ships’ engines and increased requirements in the future.

Daniel Gau, Bastian Schnöll  

The continuing increase in the demands on large diesel engines with regard to their performance, reliability and environmental compatibility means that more and more new demands are being made on ships’ engines. As a result of the increasing pressure of competition, less favourable operating conditions, smaller crews lacking in qualifications, scheduling demands and a reduction in the quality of fuel, it must also be expected that the demands on engine technology will continue to increase in the future. In today’s shipping operations, alongside high levels of capital expenditure, main and auxiliary engines represent a considerable expense in servicing and maintenance.

The development of large diesel engines with the introduction of common rail technology and the widespread use of electronic controls has led to a considerable improvement in the quality of the combustion process in the engine and thus to improved efficiency, fewer emissions and an increase in reliability.

This high quality and reliability demands very precise calibration and monitoring of the engine control parameters. Mechanical indicators, the measurement of exhaust gas temperatures and monitoring of the coolant and oil are too imprecise to produce diagnostic data for testing and/or optimising these electronically controlled processes. In this article we intend to show which features a modern measuring and diagnostic system needs in order to offer possibilities for optimising the operation of the engine.

Measuring cylinder pressure

According to classification societies, various different systems are used to determine cylinder pressure pattern – from simple spring-loaded mechanical indicators to measuring systems that require one pressure sensor for each cylinder.

The monitoring of any engine is based on high-precision measurement of the cylinder pressure pattern coupled with an investigation into the quality of the combustion. The values of and deviations in maximum pressure, compression pressure and performance are regarded as the prime indicators for the evaluation.

The aim is to minimise the load on all the engine parts (such as the bearings and crank assembly), to achieve optimum fuel combustion (thereby saving fuel) and to expose incorrect settings.

Measuring injection pressure

Essentially, the internal engine process is governed by the quality of the injection of fuel into the combustion chamber. Therefore it is self-evident that the injection pressure needs to be recorded as a measure of the injection itself and displayed with the cylinder pressure. Well-known variations are permanently installed pressure sensors in high-pressure valves or high-pressure pipes, pressure sensors in the injection pumps and the application of strain gauges to the injection line.

However, rail technology does not allow the use of one injection pressure sensor per cylinder, but only pressure monitoring within the rail itself. Pressure patterns measured at this point present oscillations that are hardly relevant and cannot therefore be interpreted meaningfully. It also seems that there are going to be problems in the future with developing measuring technology for recording pressures of up to 2000 bar.

The need for TDC correction

In order to achieve a well-founded evaluation of the cylinder pressure patterns, it is necessary to relate the cylinder pressure measurements precisely to the crank angle. In large modern diesel engines the rotation of the crankshaft can reach up to 1° KW as a result of the torsion forces in the power unit.

If no dynamic correction is made to the angle coordination, this may result in considerable errors when determining the process parameters such as the cylinder output, the start of the injection process, the start of combustion or the position of maximum pressure. When determining the cylinder output, discrepancies of up to 8% are possible here. Therefore it is hardly possible to gauge the interconnected load alignments of different stations or to analyse the injection process without using software to correct the TDC.

Many cylinder pressure measuring systems use either permanently installed rotary encoders or pick-up sensors with corresponding signal modulation on the engine to pick up a signal. In particular, there can be problems with 4-stroke auxiliary engines, since the fact that more and more engines are being encapsulated makes it more difficult to attach additional sensors.

Valve monitoring / Cylinder head assemblies

Along with the injection process, the quality of the combustion process is also determined to a significant degree by the gas exchange cycle. It is therefore desirable also to include the function of these components in the diagnosis.

In modern 2-stroke engines, valve monitoring covers the pressure of the air spring and the indication of the opening stroke. In electronic engines the switching operations of the control valves are also monitored at this point. Corresponding systems are not available for 4-stroke engines, with regard to either automation or monitoring. However, none of the alternatives described above allows for a check of the timing and leak tightness of the valves, and as a result there is no check of the adjustment setting.

Fig. 1 Cylinder pressure sensor and ultrasound sensor being used together for indexing.
Practical approaches to a solution

We have shown that well known systems – both mobile and stationary – have fallen short of the requirements described above.

MarPrime Ultra, a mobile hand-held cylinder pressure system which already meets these system requirements with a solution that takes a different approach, has been developed by Maridis GmbH. Up to now the measurement procedure has been triggered, but here it is replaced by timer-based measurements of the cylinder pressure pattern. The resulting elimination of encoders and pick-up sensors makes it possible to index all types of engines – such as 2- and 4-stroke – on board and to determine their level of performance within a short time. This means that four-stroke engines with their costly servicing can be adjusted at any time using a single measuring instrument.

TDC definition, regarded as an essential component for precise calculation, has been upgraded for this system of hand-held instruments. The software adapts a variable theoretical compression model to the pressure measurement in order to achieve the desired degree of accuracy with timed measurements in the evaluation. All the important parameters such as maximum pressure, compression pressure, indicated mean pressure, indicated performance and load distribution can thus be defined exactly.

If the combustion process is to be evaluated as a function of gas exchange and fuel injection together as cause and effect, one important piece of information about the control timings is missing. The challenge is to use measuring technology to define the opening and closing of the valves as well as to determine the point at which the fuel is injected.

Process monitoring using ultrasound measurements
Fig. 2 Cylinder pressure profile with ultrasound signal on a 2-stroke engine.


One solution for determining and monitoring the gas exchange cycle and fuel injection is to use ultrasound measuring technology. Analyses of the engine process have shown that the expansion stroke itself can be found as an emission in solids up to the ultrasound level. These emissions are superimposed on one another and are relatively difficult to separate from one another.

If the frequency band is now adjusted to higher frequencies and to ultrasound, it is possible to hear that the low-frequency mechanical emissions have been blanked out as much as possible, but other processes become apparent in their place, being separated clearly and distinctly from one another. The data includes the desired parameters, such as all the control timings and information about the leak tightness of the valve assemblies.

By applying a passive ultrasound pick-up to the cylinder head whilst measuring the cylinder pressure, it is possible to detect the ultrasound emission from the engine. Because ultrasound diffuses quickly in solids, the echoes from all the valves, as well as from the injection and ignition, are recorded without distortion. Low-frequency mechanical signals from the engine should be blanked out at this point by means of a band-pass filter in order to be able to draw clear-cut conclusions.

The indexing of the process operation by the crew remains unchanged. After the cylinder pressure sensor has been screwed onto the indicator cock, the MarPrime ultrasound sensor which is to be used for taking the measurements is fixed to the cylinder head using a magnetic grip. Once the measurements have been taken, the sensor is removed again.

At the analysis stage, plotting the individual signals with the cylinder pressure against the crank angle enables the recorded ultrasound signals to be clearly assigned. The closing of an outlet valve and the resultant slight knocking (Fig. 2 point 1) can be identified just as easily as the opening of the valve (Fig. 2 points 2) and the fall in pressure associated with this in the cylinder pressure profile. The injection ignition process (Fig. 2 point 3) with its beginning and end – a point at which the sound is very intense – can be read off and compared with the pressure profile with regard to both cause and effect.

Detecting damage and tuning the engine
Fig. 3 Cylinder pressure profile with leakages on the outlet valve in a 2-stroke engine.


The results of direct monitoring of control calibrations and settings can be checked from first-hand evidence, and the fine tuning of the engine to optimize its performance can be carried out relatively easily by repeating the measurements.

As mentioned at the beginning of this article, damage to the cylinder head tends to be diagnosed by means of indirect measurements such as monitoring the temperature of the exhaust gas. Until now it has not been possible to examine the valves whilst the motor was running and to draw conclusions about the way the vales are seated and possible leakages. This is now possible using MarPrime Ultra.

A flow of gas emits ultrasound in the same frequency spectrum. The gas exchange, characterized by the inflow of air and outflow of exhaust gases, is defined by the control timings. If the point at which the fuel enters is also blanked out, this reveals an interval before and after during which, in a functioning valve assembly, no gas flows. There are therefore also no ultrasound emissions. This is the area to which attention should be paid when looking for leakages.

One typical example of damage is a blow-by on the valve. This damage occurs when the valve seat no longer closes exactly in situ because of uneven wear and then hot exhaust gas blows through as if through a shot hole. The gas is accelerated and passes through the narrow space at increased speed, thereby emitting ultrasound. After indexing, when the cylinder pressure is plotted against the crank angle, the damage is immediately visible and can be assessed (Fig. 3, points 1 and 2).

The assignment of the leakage to the outlet valve is an important piece of information. It is possible to differentiate whether the loss of compression pressure is being caused by leakages on the outlet valve or by the seal to the combustion chamber made by the piston rings.

One further evaluation allows for differentiation between the qualities of the leakages. With regular indexing, it is possible to discover valve seat leakages and “shot holes” that are starting to develop. It is exactly this aspect that is of interest, because “shot holes” are an example of damage which does not go deep into the valve seat and is still repairable. Repairs during shipping operations involve the replacement of the valve assembly and reconditioning using on-board materials – a considerable difference in cost when contrasted with the total loss of the valve rod and the complete replacement of the sub-assembly.

Summary

The use of the MarPrime Ultra hand-held device from Maridis GmbH offers considerable advantages. These include exact measurements, an easy-to-use system and new approaches to the procedure of engine diagnosis all combined in one device. It must be borne in mind that crews are also being set new tasks and challenges as a result of the increasing complexity of motive power units.

In order to cope with these, what is needed on board is the simplest possible measuring system which will enable complex diagnoses to be made. The combination of mobile cylinder pressure measurement with the addition of ultrasound technology can be taken as a starting point from which to satisfy modern requirements for optimizing the operation of ships’ engines. The aim here is to have sufficient cylinder pressure measurements to be able to carry out an evaluation based on the condition of the engine and carry out preventative repairs, thereby increasing the certified service life of the engine and reducing costs.]

One typical example of damage is a blow-by on the valve. This damage occurs when the valve seat no longer closes exactly in situ because of uneven wear and then hot exhaust gas blows through as if through a shot hole. The gas is accelerated and passes through the narrow space at increased speed, thereby emitting ultrasound. After indexing, when the cylinder pressure is plotted against the crank angle, the damage is immediately visible and can be assessed (Fig. 3, points 1 and 2).

The assignment of the leakage to the outlet valve is an important piece of information. It is possible to differentiate whether the loss of compression pressure is being caused by leakages on the outlet valve or by the seal to the combustion chamber made by the piston rings.

One further evaluation allows for differentiation between the qualities of the leakages. With regular indexing, it is possible to discover valve seat leakages and “shot holes” that are starting to develop. It is exactly this aspect that is of interest, because “shot holes” are an example of damage which does not go deep into the valve seat and is still repairable. Repairs during shipping operations involve the replacement of the valve assembly and reconditioning using on-board materials – a considerable difference in cost when contrasted with the total loss of the valve rod and the complete replacement of the sub-assembly.

Extent of supply

Robust Travel Suitcase
MarPrime Device with Pressure Sensor
Knob to loosen Pressure Sensor
Ultra Sonic Sound Sensor (only for MarPrime Ultra)
Ultra Sonic Sound Sensor Cable (only for MarPrime Ultra)
Power Charger
Power Charger Adaptors
Network Cable
USB Cable (only for USB-version)
Software is delivered, manual to be downloaded.
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Software Diagrams

Software MarPrime main view
Software MarPrime cylinder pressure with timing & leakage
Software MarPrime changing rate of cylinder
Software MarPrime load balance bar charts with limits
Software MarPrime cylinder pressure with injecting timing
Software MarPrime history
Software MarPrime remarks and alarm list with hints
Software MarPrime report
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Information
  • New MarPrime Software Update 3.2.8 available.
  • GL Type Approval Certificate for MarPrime & MarPrime Ultra as Condition Monitoring System.
  • GL Type Approval Certificate for hardware/software & Power calculation.
  • Lloyd´s Register Type Approval Certificate for MarPrime & MarPrime Ultra as Condition Monitoring System.

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