Refine
Document Type
- Article (3)
- Conference Proceeding (1)
Language
- English (4)
Has Fulltext
- yes (4)
Keywords
Faculty / Organisational entity
The use of vegetable oil as a fuel for agricultural and forestry vehicles allows a CO2 reduction of up to 60 %. On the other hand, the availability of vegetable oil is limited, and price competitiveness depends heavily on the respective oil price. In order to reduce the dependence on the availability of specific fuels, the joint research project “MuSt5-Trak” (Multi-Fuel EU Stage 5 Tractor) aims at developing a prototype tractor capable of running on arbitrary mixtures of diesel and rapeseed oil.
Depending on the fuel mixture used, the engine parameters need to be adapted to the respective operating conditions. For this purpose, it is necessary to detect the composition of the fuel mixture and the fuel quality. Regardless of the available fuel mixture, all functions for regular engine operation must be maintained. A conventional active regeneration of the diesel particulate filter (DPF) cannot be carried out because rapeseed oil has a flash point of 230°C, compared to 80°C for diesel fuel. This leads to a condensation of rapeseed oil while using post-injection at low and medium part load operating points, which causes a dilution of the engine oil.
In this work, engine-internal measures for achieving DPF regeneration with rapeseed oil and mixtures of diesel fuel and rapeseed oil are investigated. In order to provide stationary operating conditions in real engine operation, a “high-idle” operating point is chosen. The fuel mixtures are examined with regard to compatibility concerning a reduction of the air-fuel ratio, late combustion phasing and multiple injections. The highest temperatures are expected from a combination of these control options. After the completion of a regeneration cycle, the fuel input into the engine oil is controlled. These investigations will serve as a basis for the subsequent development of more complex regeneration strategies for close-to-reality engine operating cycles with varying load conditions.
The objective of current research on internal combustion engines
is to further reduce exhaust emissions while simultaneously
reducing fuel consumption. The resulting measures often mean
an increase in complexity of internal combustion engines, which
on one hand increases production cost and on the other hand
increases the susceptibility of the overall system to defects. It is
therefore necessary to develop technologies which can generate
an advantage for the consumer despite increasing complexity.
Within the scope of the project “High Efficiency Diesel Engine
Concept” (“Hocheffizientes Diesel-Motoren-Konzept” HDMK),
funded by the Federal Ministry of Economic Affairs and Energy
with TÜV Rheinland as project management organization
(funding code: 19U15003A), two engine concepts were
investigated and combined on a John Deere four-cylinder inline
engine.
On the one hand, a new cylinder activation concept ("3/4-
cylinder concept") was implemented with the aim of reducing
fuel consumption. On the other hand, a fully variable valve train
was developed for this engine, which both improves the
functionality of the 3/4-cylinder concept and can have a positive
influence on exhaust emissions through internal exhaust gas
recirculation.
A comparison of this engine concept with its series reference
based on measurement data showed a fuel economy advantage
of up to 5.2% in the low load field cycles of the DLG PowerMix.
The maximum fuel consumption benefit in the low load engine
regime exceeded 15% in some of the operating points.
As a final step, the engine was modified for the integration into
an existing and working tractor, maintaining the available
installation space of the powertrain.
The move away from fossil fuels and the diversification of the primary energy sources used are imperative both in terms of mitigating global warming and ensuring the political independence of the Western world. For the industries of agriculture and forestry, it is possible to secure the basic energy supply through their own yield. The use of vegetable oil is a possibility to satisfy the energy requirements for agricultural machines both autonomously and sustainably. Up to now, rapeseed has been the most important plant for oil production in Western Europe. In the EU, rapeseed oil is currently credited with up to 60% fossil CO2 savings compared to conventional diesel fuel. As a result, since 2018, rapeseed oil is no longer considered as biofuel in the EU. However, if cultivation and processing are completely based on renewable energy sources, up to 90% of fossil CO2 emissions can be saved in the future. This also applies to rapeseed oil, which is a by-product of animal feed production. In addition, pure rapeseed oil is chemically unchanged and thus biodegradable, which makes it particularly attractive for use in environmentally sensitive areas.
To increase the attractiveness of rapeseed oil as a fuel for the agricultural industry, a multi-fuel concept for the flexible use of rapeseed oil, diesel fuel and any mixtures of these two fuels would be beneficial, as it minimizes economic risks due to price fluctuations, availability, and taxation. For implementing such a concept, technical adjustments to the propulsion system are necessary. In existing vegetable oil vehicles, cost-intensive additional components are required for diesel particulate filter regeneration. Conventional regeneration via post-injected fuel (which does not participate in combustion) leads to dilution of the engine oil with vegetable oil.
This study elaborates the possibilities of DPF regeneration in vegetable oil operation by internal engine measures without the need for post-injection. This includes strategies for generating exhaust gas temperatures in high-idle operation which are suitable for regeneration. For this purpose, strategies combining throttling and retarded combustion are used. The measures were successfully tested with respect to their effectiveness for DPF regeneration. It could also be proved that no increased engine oil dilution occurs as a result of the regeneration procedure.
For a prospective series application, however, regeneration should also be possible in transient engine operation. For this purpose, the measures developed for high-idle regeneration have been transferred to partial load points to gain insight into their applicability for transient engine operation. In addition, the effect of external EGR on regeneration has been considered. As the previous investigations of high-idle regeneration showed that regeneration is most critical when pure rapeseed oil is used, the studies of regeneration in part-load operation were limited to pure rapeseed oil. The systematic parameter variations carried out during the studies helped to improve the understanding of the system and the mechanisms of regeneration. The results of the investigation show that the exhaust gas temperature can be increased significantly by the measures studied. However, achieving the exhaust temperature required for DPF regeneration remains a challenge for certain operating points.
In recent years, the utilization of dual-fuel combustion has gained
popularity in order to improve engine efficiency and emissions. With
its high knock resistance, methane allows operation in high
compression diesel engines with lower risk of knocking. With the use
of diesel fuel as an ignition source, it is possible to exploit the
advantages of lean combustion without facing problems to provide
the high amount of ignition energy necessary to burn methane under
such operating conditions. Another advantage is the variety of
sources from which the primary fuel can be obtained. In addition to
fossil sources, methane can also be produced from biomass or
electrical energy.
As the rate of substitution of diesel by methane increases, the trade-
off between nitrogen oxide and soot is mitigated. However, emissions
of carbon monoxide and unburned methane increase. Since carbon
monoxide is toxic and methane has 25 times the global warming
potential of carbon dioxide, these emission components pose a
problem. Because of the stability of the molecule, methane catalysts
require an exhaust gas temperature of over 500 °C in order to work
effectively.
In this work, the effect of conventional cooled external exhaust gas
recirculation (EGR) and additional hot internal EGR are investigated
for different substitution rates in a nonroad tractor engine converted
to dual-fuel operation. The internal EGR rate is controlled by a
variable second exhaust valve lift during the intake stroke – an
approach which promises to benefit dual-fuel engines by increasing
the in-cylinder gas temperature, thus favoring more complete
combustion. A simulation model of the engine is used to determine
the internal EGR rates and in-cylinder temperatures based on the
experimental data. When internal EGR is used in combination with
external EGR, the resulting emissions show additional reductions in
nitrogen oxide (up to -51 %), carbon monoxide (up to -18 %) and
methane (up to -28 %) with increasing internal EGR, while still
maintaining low soot levels due to the substitution of diesel fuel for
methane.