Automated Combustion Analysis: Taking The Measure of Peak Performance

Monitoring diesel engine performance by traditional, manual methods is time-consuming and inherently imprecise. The limitations of those methods make it difficult to identify and pinpoint performance problems reliably. In addition, preventive maintenance routines adopted to compensate for lack of adequate data inevitably incur unnecessary costs-while the engine can still suffer from problems and imbalances that occur and remain undetected between scheduled overhauls. Ship owners and operators in fast-growing numbers are turning to automated combustion analysis to eliminate the costs of reliance on manual monitoring. In the span of a few minutes, an automated system can provide a complete, accurate picture of what is actually happening during the combustion process in each cylinder. Advanced systems operate on personal or notebook computers, capturing combustion process and fuel injection data in real time using sophisticated electronic sensors. Easily accessible in familiar formats, the data they provide can be used to optimize both the mechanical operation and ignition timing of each cylinder. The savings from the resulting improvement in fuel consumption and combustion performance are obvious benefits of a well-tuned engine. Automated monitoring also allows accurate, detailed diagnosis of indicated power across all cylinders for efficient correction of thermal stress and load imbalances. Proper balancing reduces the stress and wear on engine parts for longer service life and lower operating and maintenance costs. To illustrate the unique contribution that automated monitoring makes to achieving maximum efficiency and savings, we will look at two recent shipboard applications utilizing the DPA DIESEL PERFORMANCE ANALYZER* from Ashland Specialty Chemical Company's Drew Marine Division. We will also examine more closely the impact of automated analysis on the typical engine maintenance profile. Added parameters for precise diagnosis In our first case, a training exercise using a portable unit onboard a Mediterranean cruise ship paid an extra dividend by documenting and diagnosing a pair of previously unsuspected engine problems. Bar charts generated by the automated system immediately identified low Compression Pressure in one cylinder of the vessel's four-stroke, medium-speed engine. Typical of many similarly powered vessels, ship engineers previously relied on exhaust gas temperature (EGT) and peak cylinder pressure readings for periodic assessments of the engine. However, compression pressure anomalies on four-stroke, medium-speed engines are almost impossible to detect and confirm based only on those measurements. The system's additional measurement of Angle at Fuel Ignition made it easy to pinpoint the compression problem by ruling out ignition timing as a factor. The engineer was then able to focus the investigation on possible mechanical causes, such as worn piston rings, damaged liner or leaking valves. The solution was likely to be relatively inexpensive, while the cumulative costs of higher fuel consumption and escalating damage due to the undetected problem could have been substantial. In addition, the Mean Indicated Pressure chart generated by the system showed an unbalanced engine with two high-load and two low-load cylinders. An analysis of all available parameters showed ignition timing issues with possible mechanical causes for two cylinders, which needed to be investigated before adjusting fuel pump timing. The pieces of the picture provided by EGT and peak cylinder pressure data alone were not sufficient to tune the engine effectively in this case. A supplemental report provided to the ship engineer highlighted the importance of analyzing all factors in aggregate to avoid actions that could worsen the thermal load, instead of improving it. The report also documented the resonance effect on the indicator line of a four-stroke, medium-speed engine. Pressure pulses reflecting the length and shape of the indicator tube mounted on the valve can increase maximum pressure by 2 to 5 bar. Correction for the distortion, which the DPA system calculates using a unique digital method, is a requirement for reliable accuracy in automated systems. Accuracy to within 0.1 bar on the pressure diagram, as well as 0.1 degree on the crankshaft measurements, is available with the most advanced systems. Injecting the fuel side into the picture An additional sensor for the high-pressure fuel line, available as an option with some automated systems, can provide data for monitoring injecting pressure, greatly simplifying the analysis and correction of fuel-side problems. After installation of a DPA system onboard a container vessel calling in the Pacific Rim, the option easily paid for itself with a fast diagnosis of a leaking fuel pump. Although relatively common, it is difficult to detect leaking fuel pumps using common, manual tools, including the draw cards used previously to indicate this vessel's main engine. And like most circumstances where deterioration in mechanical parts starts to impact performance, failure to identify the problem and act promptly can easily result in more costly breakdowns and repairs in the future. In this case, the Mean Indicated Pressure bar charts following a routine measurement showed an anomaly in one cylinder. A quick review of the data showed no difficulties with compression pressure, and the Injection Pressure charts immediately confirmed the most likely problem, allowing timely replacement of the leaking pump. Maintenance by the facts-instead of by the book Because of its ease and convenience, many ship engineers are using automated combustion analysis to look at their engines periodically-some even take weekly measurements. As demonstrated by both cases discussed above, this kind of monitoring can catch problems early and simplifies tuning the engine for peak efficiency. Two-stroke engines monitored with the DPA system can even be adjusted while running, allowing immediate correction without disrupting operating schedules. With reliable data, operators can do maintenance and make repairs when they are needed, based on the documented condition of the engine. As a result, automated analysis is also revolutionizing engine maintenance practices. It is no longer necessary to open up the engine and replace components at regular intervals based on the calendar or running hours. Instead, the intervals between maintenance or overhauls can be extended with confidence, provided the monitoring system confirms that the engine is balanced and all combustion parameters are within normal limits. Acceptance of the concept of condition-based engine maintenance is growing, as manufacturers continue to build more "intelligence" into the engines themselves using electronics and sensors. There are also signs of official endorsement. At least one classification society is preparing guidelines for its use and possible exemptions from requirements for periodic inspections. As owners and users attest, automated combustion analysis pays back its cost very quickly in manpower, equipment and operating savings. And more reliable engine performance also means safer ships. With more data and better data for monitoring that performance, everybody gains. Article courtesy of Rob Van Solingen, Product Manager, Engineered Systems & Products, Ashland Specialty Chemical Company, Drew Marine Division.