Everyone knows the MTU Series 4000. It has earned its place in everyone’s world. Powerful and reliable, it meets today’s emissions requirements and is fuel-efficient. You will find it in ships as well as in haul trucks and gensets. Since launching them in the market 15 years ago, MTU has sold more than 26,000 Series 4000 engines. And nearly all of them are different – because there is no such thing as the Series 4000 engine. In fact, hardly a single engine in the series is identical to any other – every unit is specifically matched to the individual customer’s needs. That makes Series 4000 truly and universally unique. So what distinguishes the universal engine from the unique, customer-tailored unit?
The skipper of an inland waterways vessel may get 880 kW from his Series 4000 unit whilst a haul truck operator can expect 3,000 kW from his. One engine may have 16 cylinders, another only 8. One will develop 2,500 bar injection pressure while another operates at 1,800 bar. One will have a diesel particulate filter while the other does not need one. The permutations are endless. Everyone talks about the Series 4000 engine – which is alright in a way – but, as attractive as it may be, the concept of building one engine that is perfect for all applications is simply utopian. In reality, on MTU Series 4000 engines, only major components such as the crankcase, crankshaft and flywheel housing are identical - or more accurately, very similar, because even they vary. One common factor did exist, however, when they were introduced in 1997: all Series 4000 engines had a cylinder capacity of just over four liters, which is where the series designation comes from. Today's cylinder capacity is a little higher at 4.77 liters, so even here differentiation is necessary.
Requirements make the difference
Engines that propel ships, for example, need completely different cooling systems from those that power haul trucks. Ships have dual-circuit cooling systems that utilize the water the vessel is moving in to cool the engines. On haul trucks or locomotives, excess heat is dissipated into the atmosphere, so they need suitably powerful cooling systems. The two applications also use different safety technology. Marine certification authorities stipulate that surface temperatures on marine engines must never exceed 220 C. With just a few exceptions, ships normally operate at sea level, while haul trucks operate in mines that are often located at altitudes of several thousand meters. To make sure that these truck engines get enough air for combustion, MTU engineers have developed turbocharging technology specifically for these conditions. Mining engines also need to be extremely robust when it comes to environmental influences such as the extremes of cold, heat and dust-laden air that often prevail. Other applications demand different criteria: on genset engines for example, the ability to ramp up to operating speed as fast as possible is critical. Emergency gensets in nuclear power stations need to get up to full power in just a few seconds. And there is yet another factor that decisively affects engine tuning, namely the time interval available between major overhauls. With yacht engines, this can be as little as 9,000 hours, whilst the engine in a shunting locomotive has to last for 30,000 hours between overhauls.
Emissions limits make all the difference
Over the last ten years, the differences between engines have been increasingly driven by another factor: the emissions limits they have to comply with. To minimize pollutant output from diesel engines, the European Union and the US Environmental Protection Agency (EPA) have specified emissions limits. These are not the same everywhere, but vary widely depending on application and region. In some cases, they are even interpreted differently by individual countries or cities. This is where the dream of building the universal engine finally fades from view.
Modular technology for Series 4000
MTU engineers have developed a modular concept involving an entire bundle of technologies that either avoid the generation of pollutants altogether, or prevent them from entering the atmosphere. The system includes the following elements:
> Increased injection pressure up to 2,500 bar: The higher the pressure at which fuel is injected into the combustion chamber, the more finely it is vaporized. As the vapour becomes finer, fuel combustion improves and fewer soot particles are formed. Multiple injection is also key here. This involves additional fuel injections both before and after ignition, and these cut down soot formation.
> Miller process: To reduce nitrogen oxide emissions, the inlet valves on each cylinder are closed just before the piston reaches bottom dead centre so that the air in the cylinder expands and cools. The process decreases nitrogen oxide emissions by up to 30%.
> Exhaust gas recirculation: Depending on the application in question, up to half the exhaust gas is first cooled and then returned to the engine. This lowers combustion temperature and reduces the generation of nitrogen oxides.
> Exhaust gas aftertreatment with SCR: To reduce nitrogen oxide emissions even further, MTU employs SCR technology on some engines. Here, an aqueous urea solution is introduced into the exhaust stream. The urea is converted into ammonia, which transforms the nitrogen oxides into harmless water and nitrogen in the catalytic converter. The chemical process is selective because only nitrogen oxides are reduced and unwanted side-reactions are largely suppressed.
> Exhaust gas aftertreatment with diesel particulate filters: Here, diesel particulate filters (DPFs) are used to prevent soot particles exiting the engine. Exhaust gases are routed through channels with porous walls that allow the exhaust to pass through, but filter out soot and other particles. This can reduce particle emissions by up to 99%.
> Two-stage turbocharging: For the first time, this technology makes two-stage, controlled exhaust turbocharging with intermediate cooling available for engines in haul trucks, trains and oil pumps. The Miller combustion process and exhaust recirculation technology both require increased charge-pressure. In the first stage of a two-stage turbocharging system with two turbochargers, the air is precompressed in a low-pressure turbocharger before undergoing intermediate cooling followed by secondary compression in a high-pressure turbocharger. This satisfies the need for increased charge-pressure and achieves a high level of turbocharging efficiency. It also makes it possible to build more compact diesel particulate filters.
> No matter which system modules the MTU development engineers select, they are all controlled by the engine management system. Whilst earlier engine management systems controlled only engine speed and injection pressure, they now cover five parameters. For example, additional sensors in the exhaust tract now calculate how much exhaust needs to be introduced into the flow of fresh air to ensure that the combustion temperature drops to a level where the nitrogen oxide content in the engine exhaust remains below specified limits. At the same time, the oxygen content has to be adjusted to suit the load point. In cases where exhaust gas recirculation is also involved, the level of complexity increases even further, since the engine electronics must also control regeneration of the diesel particulate filter. Various parameters such as exhaust temperature, the number of hours of operation since the previous regeneration phase and differential pressures across the filter are used to calculate exactly when filter regeneration is required.
Individual engine concept for each application
By combining these modules and meeting the demands arising from individual applications, MTU engineers configure many different Series 4000 engines for ferries, workboats, submarines, frigates, gensets, haul trucks, trains and drilling pumps. For example, the rail engine that MTU
introduced at the 2010 Innotrans Exhibition was the ?first MTU engine to be fitted with a diesel particulate filter for series production. The filter unit is integrated in the locomotive in place of the silencer and also functions as a silencer, thereby saving space. In contrast, the MTU rail engine for the American market has no diesel particulate filter because EPA Tier III particulate limits are higher. Likewise, MTU Series 4000 engines for haul trucks comply with specifications without the need for diesel particulate filters. MTU began equipping its Series 4000 genset engines with SCR technology as early as 2011 in order to counter nitrogen oxide emissions. From 2016, all of its Series 4000 engines for workboats will be able to meet IMO III regulations using SCR technology alone. Customer requirements create the truly unique unit Of course, that is not the end of the story. While we may have the perfect engine for trains, haul trucks or ships, the requirements of the individual customer now come into play. Every locomotive, every ship and every haul truck that is to be powered by a Series 4000 engine is different, and this is where the work of the MTU applications engineers begins. Their task is to tailor the Series 4000 engine configured from the technology modules to perfectly match the customer’s specific needs. What traction system does he want? Does he need a diesel-electric drive with a diesel engine powering an electric motor or is direct diesel drive required? What extra components are needed? What installation space is available? Which interfaces are required? The questions are neverending and they all need perfect answers, worked out over months and sometimes years of painstaking work.
Only when all these questions have been answered is the customer's unique Series 4000 engine complete.
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