A tognum Group Brand
Engine technology
Turbocharging:
Key technology for high-performance engines
Authors: The performance of an internal combustion engine can be increased by adding tur-
bocharging. A turbocharger compresses the air so that more oxygen flows into the
Dr. Johannes Kech combustion chamber. In this way, more fuel is burned and the power output of the
Head of Development Turbocharging, engine increases accordingly. The turbocharger is driven by exhaust gas, which makes
Fuel Injection and Components turbocharged diesel engines very efficient. MTU develops this key technology for
high-performance engines in-house.
Ronald Hegner
Team Leader, Design of Turbocharging Systems Turbocharger development and production at MTU engine power ratings from 400 to 9,100 kW.
Turbocharging is an integral component of the Turbochargers are purchased for engine designs
Tobias Männle engine design concept. It shapes the character- in which synergy effects with the commercial
Team Leader, Fluid Dynamics and Thermal istics of the engine more than almost any other vehicles sector can be used.
Analyses system, as it affects its economy, dynamics and
emission characteristics. This is why turbocharg- The global market for turbochargers is dominat-
ing is one of MTU’s key technologies. MTU has a ed by car and commercial vehicle applications.
tradition of maintaining the expertise for devel- By comparison, the number of turbochargers
oping and producing its turbochargers in-house. fitted to industrial engines is negligible. The re-
The range of MTU turbochargers extends across sult is that turbocharger manufacturers rarely
www.mtu-online.com
produce specialized designs for industrial engine
Fig. 1: Current MTU turbocharger program (ZRT 12, 13, 35, 36, 57)
manufactures. Where customers’ requirements
MTU’s current turbocharger family includes five series and is based on a concept of using as many
of the engines are such that they cannot be sat- common parts as possible.
isfied by purchased turbochargers, MTU devel-
ops and produces the turbochargers itself.
A exhaust inlet
Taking all engine series into account, MTU pro- B exhaust outlet
duces roughly 50 percent of the turbochargers C charge air inlet
in-house. The present range of MTU turbo D charge air outlet
chargers encompasses five series — the ZRT 12, cooling water
ZRT 13, ZRT 35, ZRT 36 and ZRT 57 (see Figure
1), and is based on a concept of using as many
common parts as possible. In the case of the
new Series 4000 engine for rail applications with
regulated two-stage turbocharging, for instance,
all three turbochargers in the system are identi-
cal. This simplifies the logistics in production and
the supply of spare parts to customers.
Due to its in-house development and production
of turbochargers, MTU is in a position to meet
customer demands for highly responsive and pow-
erful engines. MTU matches the turbocharging
system to the engine so that it delivers reliable 1 turbine wheel
high performance across the entire range of en- 2 compressor wheel
gine specifications, from sea level to an altitude of
3 pressure ratio p2t/p1t
4,000 meters, and from low to extremely high
ambient temperatures. As the MTU turbochargers 4 reduced volumetric flow Vred.
are configured specifically to meet the engine
specifications, they are easily integrated into the small size series ZRT 12, ZRT 13 medium size series ZRT 35, ZRT 36 large size series ZRT 57
overall engine package. This makes the engines 1 Ø 103-123 mm 1 Ø 158-185 mm 1 Ø 245 mm
very compact — a decisive advantage in applica- 2 Ø 115-135 mm 2 Ø 179-210 mm 2 Ø 265-270 mm
tions where installation space is at a premium. 3 up to 5.2 3 up to 5.4 3 up to 5.4
4 0.2-0.9 m3/s 4 0.8-2.0 m3/s 4 1.8-3.5 m3/s
In recent years, the operating conditions of some
applications have become tougher. The power cles, which also has an effect on the service life es into account in the development of its turbo-
units are subjected to a high number of load cy- of the turbochargers. MTU has taken these chang- chargers, has further optimized the time between
overhauls (TBO) and brought this in line with the
Fig. 2: Use of three-dimensional computation procedures for simulating the airflow and the mecha- engines. In the case of the Series 4000 rail en-
nical structural loads to optimize turbocharger performance gine, for example, turbocharger TBO is as high as
The turbochargers must retain the required characteristics throughout their entire service lives. To this
15,000 hours depending on the number of load
end, MTU works with three-dimensional computation procedures to simulate the airflow and the mechani-
cal structural loads. cycles per hour. This means short maintenance
periods and costs — this also applies to the turbo-
chargers. In the turbocharger development proc-
esses, MTU makes use of the possibilities offered
by efficient calculation and simulation tools.
When a new turbocharger is produced, it has
already gone through a whole sequence of analy-
tical optimization processes in thermodynamics,
structural mechanics, durability and containment
strength, for example, by the time it is put on the
test bench. Analysis fundamentally involves opti
mization of the component by the use of three-
dimensional computation procedures for simu-
lating the airflow and the mechanical structural
loads (see Figure 2). In this way, MTU ensures
that the turbochargers have the required char-
acteristics when they finally go into service and
retain them throughout their entire service lives.
Turbochargers are subjected to high thermal
loads in operation. Accordingly, seals and bear-
Turbocharging: Key technology for high-performance engines | MTU | 2
With variable turbine geometry, the power delivery and response
characteristics of the turbocharger can be better adapted to the
dynamic engine operating conditions. The exhaust passes over
adjustable guides to the turbine blades so that the turbine spools up
quickly at low engine speeds and subsequently allows high exhaust
gas flow rates.
Turbocharger with variable turbine geometry (VTG)
ings are thermally isolated and, if necessary, turbocharging is matched to the specific For applications that demand even more dynamic
water-cooled. To limit the surface temperature, equirements of the particular application. power response, particularly in marine applica-
MTU uses a water-cooled impeller blade on This means that a power generation engine, tions, MTU uses the sequential turbocharging
highly turbocharged engines, which simultane- which always runs at the same speed, needs principle. It involves multiple turbochargers be-
ously relieves some of the load on the inter- a different turbocharger setup than a vehicle ing sequentially linked. One turbocharger pro-
cooler. In marine applications, the turbine is engine. A vehicle engine is driven dynamically duces the boost pressure for low engines speeds,
cradled in a water-cooled connecting block — it has to deliver high performance from idling and when the engine is revving faster or when
(see Figure 3). The turbochargers thus also speed right through to maximum revs — and more power needs to be developed, additional
satisfy the SOLAS Directive (Safety of Life at the turbocharger characteristics have to be turbochargers are added so that sufficient air
Sea) for marine applications, which stipulates matched to the broad power band. The chal- is delivered to the cylinders.
that, for safety reasons, the surface tempera- lenge is that a turbocharger can be set up
ture may not exceed 220 degrees Celsius. either for a wide speed range or a high boost To provide highly responsive engine dynamics,
pressure. For engines earmarked for dynamic the Series 890 engines, which are designed for
Implementation of turbocharging at MTU applications, therefore, MTU has designed the high performance in military vehicles, have vari-
As a matter of principle, MTU equips all en- turbochargers to deliver sufficient boost pres- able turbine geometry. With this technology, the
gines from the various engines series with sure while covering as broad a range of engine exhaust passes over adjustable wings to the tur-
turbochargers. Within a design series, the speeds as possible. bine blades so that the turbine spools up quick-
ly at low engine speeds and subsequently allows
high exhaust gas flow rates. For the new engine
generations to achieve high performance, MTU
uses two-stage turbocharging. In the early 1980s,
MTU already equipped the Series 1163 with com-
pletely integrated two-stage turbocharging with
intercooling. Up to five sequentially arranged tur-
bocharger groups consisting of high and low-
pressure stages enable the engine to deliver
7,400 kW of power.
New demands on turbocharging due to new
emissions legislation
Today, the ongoing development of engines is
definitively determined by the continual tightening
of emissions standards. This means that addi-
tional systems that prevent the production of
diesel particulates or nitrogen oxides during the
combustion process or clean them further down-
stream such as the Miller process, exhaust gas
recirculation (EGR), selective catalytic reduc-
tion (SCR) or a diesel particulate filter (DPF) have
to be integrated into the overall engine design
concept. For MTU, turbocharging is one of the
key technologies in these low-emission con-
cepts. This is because it is only with a compat-
Fig. 3: High-performance turbocharger with water-cooled casing and compressor impeller
Using water cooling for the casing and compressor impeller ensures that the engine’s surface tempe- ible turbocharging system that the tendency of
rature is limited, which makes MTU turbochargers thermally very durable. these additional systems to negatively affect
engine performance and responsiveness can be
Turbocharging: Key technology for high-performance engines | MTU | 3
prevented. A common feature of all emissions- er system is integrated into MTU’s electronic second downstream of the high-pressure stage.
reducing technologies is that they diminish engine management system ECU ( Engine Con- Intercooling provides more efficient compression
the effect of the turbocharging. The Miller proc- trol Unit), which was developed in-house. in the following high-pressure stage, which leads
ess, exhaust gas recirculation and diesel partic- to a higher efficiency level of the turbocharging
ulate filter create higher exhaust backpressure; The innovative regulated two-stage turbocharging system. In the case of all MTU engines, the inter-
exhaust gas recirculation increases the air mass system is being used for the first time for the new coolers are highly integrated into the engine unit
that has to be delivered to the cylinder. To put it Series 4000 engine for rail applications. It meets and have a very small space requirement.
simply, the turbocharger has to compress the air EU Directive 97/68/EC Stage IIIB emission re-
at a higher rate, i.e. it must force more air into quirements that come into force for diesel loco- Summary
the combustion chamber to provide the same motives in Europe in 2012. Regulated two-stage Turbocharging helps MTU engines to achieve
amount of oxygen for combustion as before. turbocharging is also definitely planned for low fuel consumption and high performance
future versions of the Series 1600, 2000 and across a broad range of operating speeds. In
As research by MTU has shown, the single- 4000 engines in other mobile applications such addition to MTU’s other key technologies, it is
stage turbocharging previously used will no as construction and industry. For stationary appli- a major component of the strategies to comply
longer be sufficient for most applications in cations such as power generation, in which the with the increasingly tougher emission restric-
the future. For engines designed to comply demands on turbocharger dynamic response are tions to come without sacrificing engine per-
with tough emissions standards, the specialist not so high, the more economical single-stage formance or efficiency. The company has a
for propulsion solutions will opt for regulated turbocharging will continue to be used. tradition of developing and producing its own
two-stage turbocharging (Figure 4). This is a turbochargers for high-performance applica-
system that ensures a constantly high rate of Intercooling tions in-house. They are configured specifically
intake air delivery to the engine at all operat- When the air is compressed by the turbocharger, to satisfy the high demands of the engines
ing points and even under extreme ambient it heats up. Intercooling further increases the air in terms of economy, performance, dynamic res-
conditions (intake air temperature, altitude, density so that greater air mass and thus more ponse and service life. Because of the high
backpressure). It involves pre-compression of oxygen enters the cylinder. The regulated two- level of integration of the MTU turbochargers
the intake air by low-pressure turbochargers stage turbocharging system works with two inter- in the engine package, customers benefit
followed by further compression in high-pres- coolers. The first is located between the low- from a compact engine design with a low
sure turbochargers. Control of the turbocharg- pressure and the high-pressure stage, and the space requirement.
Fig. 4: Regulated two-stage turbocharging to meet
future emission standards
Since single-stage turbocharging will no longer be
sufficient to comply with the increasingly tougher future
emission standards, MTU in future will opt for a regulated
two-stage turbocharging.
1 charge air cooler
2 intercooler
3 low-pressure compressor
4 low-pressure turbine
5 high-pressure turbine
6 high-pressure compressor
A from high-pressure compressor to charge air cooler
B from charge air cooler to cylinder bank
C intake air
D exhaust outlet
E from intercooler to high-pressure compressor
Turbocharging: Key technology for high-performance engines | MTU | 4
Glossary
Single-stage turbocharging
In the case of single-stage turbocharging, the boost
pressure for the entire range of engine speeds and
loads is generated by a single turbocharger.
Sequential single-stage turbocharging
In the case of sequential single-stage turbo
charging, individual turbochargers are added
sequentially in parallel depending on the engine
speed and load by means of valves in the intake
and exhaust systems.
Turbocharging: Key technology for high-performance engines | MTU | 5
Glossary
Photo credits: Page 1 to 8, Adam Wist for MTU Friedrichshafen GmbH.
Sequential two-stage turbocharging
Basically speaking, sequential two-stage tur-
bocharging operates in the same way as
sequential single-stage turbocharging. However,
instead of an individual turbocharger in each
case, a pair of turbochargers is added or
disconnected as required.
Regulated two-stage turbocharging
In the case of regulated two-stage turbocharging, two
turbochargers are connected in series. In the system
configuration employed by MTU, the exhaust flow from the
cylinders is split so that part of it passes through the
high-pressure (HP) turbine and the rest is diverted through a
bypass by a controllable wastegate valve. The entire mass
flow then flows through the low-pressure turbine (LP).
MTU Friedrichshafen GmbH, Maybachplatz 1, 88045 Friedrichshafen, Germany, Phone +49 7541 90-0, www.mtu-online.com August 2011
MTU is the brand name under which the Tognum Group markets
engines and propulsion systems for ships, for heavy land, rail and
defense vehicles and for the oil and gas industry. They are based
on diesel engines with up to 9,100 kW and gas turbines up to
45,000 kW power output. The company also develops and produces
bespoke electronic monitoring and control systems for the engines
and propulsion systems.
