MITSUBISHI Lean-burn Gas Engine with World's Highest ...

1 MITSUBISHI Heavy Industries, Review (Aug. 2003)1 MITSUBISHI Lean-burn GasEngine with World's HighestThermal EfficiencyMitsubishi Heavy Industries, Ltd. (MHI) manufactures low NOx Lean-burn gas engines in a wide output rangefrom small output "GSR" to large output "MACH-30G". MACH-30G is featured a micro pilot with powerful ignitionenergy replacing spark plugs at an output of 3 650 to 5 750 kW, and GSR has a compact package featuring a Millercycle, covering an output range of 280 to 845 kW. Each Engine has achieved the World's Highest electrical efficiencyof 44% and 40%, respectively, in each output range. At present, more than 20 sets of each model are in service, andtheir high performance and reliability are highly Introduction1. Introduction1.

2 Introduction1. Introduction1. History of development of high - efficiency History of development of high - efficiency History of development of high - efficiency History of development of high - efficiency History of development of high - efficiency gasengineengineengineengineengineUnder the background of increasing need for lowerCO2 emission recently, in the field of power generationengines there is an increasing demand for gas enginesfeaturing low emission of harmful constituents such asCO2, NOx and particles. Accordingly, MHI has developedlow NOx Lean-burn gas engines by introducing the lat-est technologies in order to achieve the World's highestelectrical efficiency . MHI has already succeeded in de-livering gas engines with the Highest thermal efficiencyin the world, namely, MACH-30G with pilot ignition sys-tem using a little fuel oil as ignition source in the 5 000kW class, and GSR using the miller cycle in the under1 000 kW class, and is receiving good Lineup of MHI gas Lineup of MHI gas Lineup of MHI gas Lineup of MHI gas Lineup of MHI gas enginesTTTTT able 1able 1able 1able 1able 1 shows specifications in comparison with thoseof conventional engines.

3 MACH-30G has its brake meaneffective pressure (BMEP) raised from 13 bars to 20 bars,the equivalent level of a diesel Engine , and has also beenimproved in its electrical efficiency from the to by the introduction of a pilot ignitionsystem and combustion control system. The appearanceof MACH-30G plant is shown in Fig. 1 Fig. 1 Fig. 1 Fig. 1 Fig. 500/1 8001135150170/1801 200/1 5001240150 Table 1 Specifications of MHI gas enginesMACH-30 GConventional typeConventional typePilot ignitionMiller cycleGenerator output (kW)Cylinder bore/stroke (mm)Speed (rpm)BMEP (bar)Electrical efficiency (%)NOx (ppm, O2 = 0%)FeaturesLean- burn with pre-combustion chamberLean- burn with pre-combustion chamberPilot ignitionMiller cycle(with de-NOx system)Spark ignitionSpark ignition2 400 - 3 7503 650 - 5 750320 - 1 015280 - 845 Fig.

4 1 Appearance of MACH-30 GAppearance of MACH-30G installed at a plant in TSUNODAHIROMI SHIMODATATSUO TAKAISHI2 MITSUBISHI Heavy Industries, Review (Aug. 2003)GSR gas Engine features improved electrical efficiencyfrom 35% of conventional engines to 40%, thanks to anexpansion ratio and introduction of a miller cycle thatenhances the cycle efficiency with a high - efficiency MACH-30G and GSR, MHI offers gas engines ofhighest efficiency in a wide range from small to Features of MACH-30G2. Features of MACH-30G2. Features of MACH-30G2. Features of MACH-30G2. Features of MACH-30 GThe features of MACH-30G are shown Pilot ignition Pilot ignition Pilot ignition Pilot ignition Pilot ignition systemFig. 2 Fig. 2 Fig. 2 Fig. 2 Fig.

5 2 shows the features of the pilot ignition systemin comparison with conventional spark ignition. Insteadof ignition using conventional spark plugs, the pilot ig-nition system features ignition of gas in a pre-combustionchamber by injecting (1% or less in calorific ratio) a littlefuel oil from a pilot injector. The pilot fuel is very smallin quantity but has a powerful ignition energy roughly8 000 times that of a spark plug, so that combustion isstable and efficiency is improved. Moreover, owing tothe potent ignition energy, there is no need to prepare ahigh-concentration air-fuel mixture in the pre-combus-tion chamber as required in spark ignition engines, andproduction of NOx in the pre-combustion Engine is low-ered. As a consequence quite low NOx of 100 ppm (O2 =0%) has been realized for the first time in the industry,which is less than half the emission by other manufac-turers, and local regulations can be met withoutinstalling a de-NOx maintenance interval of a fuel injection valve forpilot ignition is 4 000 hours, which is more than doublecompared with 1 000 to 2 000 hours for ignition plugs.

6 In addition, by using powerful ignition energy, the sys-tem can stably burn various low calorie gases such asbio gas and pyrolysis Combustion control system M-RICS ( Combustion control system M-RICS ( Combustion control system M-RICS ( Combustion control system M-RICS ( Combustion control system M-RICS (MitsubishiReal-time Intelligent Control System)Real-time Intelligent Control System)Real-time Intelligent Control System)Real-time Intelligent Control System)Real-time Intelligent Control System)Fig. 3 Fig. 3 Fig. 3 Fig. 3 Fig. 3 shows M-RICS (a registered trademark of MHI),a combustion control system using electronic fuel sup-ply system and combustion diagnosis unit of M-RICS, the combustion condition is diagnosed in nineranks depending on the combustion pressure obtainedby directly sensing with a cylinder pressure sensor in-stalled in each cylinder, and the combustion is controlledby automatically adjusting the volumes of pilot fuel andfuel gas and the timing individually in each cylinder bymeans of a main controller, DIASYS (a registered trade-mark of MHI).

7 As compared with conventionalvibration-type knock sensors, each cycle can be controlledat a high response by means of a solenoid operated pilotfuel injector using a common rail system and gas ad-mission valve, realizing the following features (patentpending).(1) Improved efficiency by balancing combustion in allLean mixtureLean mixtureSpark ignitionSupply of pilot fuelPilot injector (ignition energy 800 J)Pre-combustion chamber ( lean mixture)Flame from pre-combustion chamber (Combustion in main combustion chamber)Main combustion chamberPilot ignition systemFig. 2 Comparison of pilot ignition system and spark ignitionInstead of conventional spark ignition, MACH-30G uses the pilot ignition system whose ignition energy is 8 000 times supply of fuel gas into pre-combustion chamberSpark plug (ignition energy J)Pre-combustion chamber (rich mixture)Gas supply electromagnetic valvePressure sensorTurbochargerMACH-30 GFig.

8 3 Electronic fuel supply system and combustion diagnosis system M-RICSM-RICS optimizes control of combustion state of Engine at all times by using main controller fuel supply (common rail) systemGeneratorElectronic governorPilot controllerCombustion diagnosis unit M-RICSMain controller DIASYSM itsubishi Heavy Industries, Review (Aug. 2003)3cylindersThe pilot ignition timing can be adjusted automati-cally on the basis of the diagnosis result of combustionpressure, and the combustion of each cylinder can bebalanced all the time. As a result, all cylinders oper-ate at maximum efficiency , which greatly improvesthermal efficiency .(2) Optimum control against calorific fluctuationsM-RICS diagnoses and controls the firing pressureitself optimally in spite of calorific fluctuations of thefuel or aging of components.

9 Accordingly, optimumcombustion is always adjusted automatically and highefficiency is maintained for a long period. At present,a plant using four types of LNG with different calo-rific values is operating steadily.(3) Avoidance of abnormal combustionFig. 4 Fig. 4 Fig. 4 Fig. 4 Fig. 4 compares the cylinder pressure trace fromM-RICS in knocking and single of vibration-typeknock sensor of other manufacturers. Since M-RICS senses the cylinder pressure directly, abnormal com-bustion can be diagnosed with high precision, theinjection timing and amount of pilot fuel are con-trolled, and abnormal combustion is eliminated. It alsohas an automatically fuel cut system "capable of con-tinuing power generation without stopping Engine incase of unexpected trouble" which is important in anengine for power generation, therefore any accidentcan be avoided with ample allowance.

10 (4) Preventive maintenance function by diagnosis of ab-normalityIn the remote monitoring system of MACH-30G,combustion control data of M-RICS is monitored atthe remote monitoring center. As compared withconventional diagnosis of abnormality by tempera-ture or pressure level, a more precise and promptdiagnosis of abnormality is possible, and preven-tive maintenance functions will be Production and order Production and order Production and order Production and order Production and order booksTTTTT able 2able 2able 2able 2able 2 shows order books and deliveries of MACH-30G. A total of 19 sets in five plants were ordered in2001, and the first and second sets were put into com-mercial operation in October 2002 at MHI YokohamaPower (MYP) in MHI Yokohama Dockyard & MachineryWorks.