Heavy-Duty-, On- und Off-Highway-Motoren 2023

Climate neutral by 2050 – this is what the EU has committed to with the European Climate Change Act in order to limit global warming to 1.5 °C.

With its emission targets and legislation, the EU is aiming for zero-emission road traffic by 2050. The new EuVII emissions standard is intended to be an intermediate step on this path. In particular, it provides for a tightening of the NO_x limits. However, the technological effort required and the associated rising costs for vehicles are disproportionate to the marginal NO_x reduction potential, which has no significant impact on air quality. In order to achieve the goal of local zero-emission mobility as quickly and efficiently as possible with the available resources, the focus should be on alternative drive systems and the possibility of converting existing vehicles to regenerative fuels.

MAN is aiming for all new commercial vehicles sold from 2040 onwards to be powered by fossil-free fuels.

In order to further accelerate the transition to zero-emission powertrains, which is urgently needed in terms of the fight against climate change, MAN has joined forces with Friedrich Alexander University of Erlangen-Nuremberg and Nuremberg Institute of Technology to establish the Future Driveline Campus. The aim of this three-way alliance is to share and further expand the existing high-quality infrastructure, such as analysis equipment and test benches, and to jointly research and develop ideas for locally emission-free drives in close cooperation between industry and science.

The target in decarbonization of vehicles in Offroad sector will become more and more stringent due to future cities restriction regarding the CO₂ emissions and to the different target defined from EU for decarbonization of different sectors. Certain Offroad vehicles such as mobile crane are operating in cities with crane mode, but also the vehicle can be driven in the motorway with the equipment. A certain flexibility of power train is required to cover both operation modes. One of the main challenges of hydrogen is the volumetric energy density of the fuel which has an impact on the size of the hydrogen tank. By replacing a certain amount of required energy using HVO (Hydrotreated Vegetable Oil, or diesel) as fuel, it will have a significant impact on the total power train volume.

The hydrogen dual fuel solution has a potential to offer a significant improvement in terms of CO₂ emission reduction in Tank-to-Wheel using Diesel or HVO as a pilot fuel. The dual fuel (DF) concept (hydrogen/diesel or HVO) represents a possible solution to decarbonize some Off-Road application. Additional advantage of DF is its potential to retrofit the current diesel engines by smart integration of hydrogen injectors in the intake manifold, while conventional injection of HVO (or Diesel) into the cylinder for ignition of the premixed mixture (air/fuel) is used.

The development of the technology has started by design and simulation which leads to combustion architecture definition. The experimental investigation of dual fuel operation has been performed on 4-cylinder engine (9 L). Several combustion layouts for hydrogen injection such as port fuel (PFI) and direct injection (DI) configuration has been considered in the analysis. The best configuration has been selected for testing of several OFF-Road cycles to evaluate the technology performance in terms of power density and emission in real vehicle operations. Afterward, an outlook regarding further application of the hydrogen dual fuel engine has been illustrated regarding the size of the complete power train (Fuel tanks, engine, cooling unit, etc.…) in different control of energy management configuration. At the end, a complete technology evaluation with several integration studies of the power train have been conducted and analyzed for different vehicle types.

One of society’s most important goals for the coming years and decades is to reduce greenhouse gas (GHG) emissions. A successful energy transformation includes the switch from fossil fuels to sustainable energies. Hydrogen will play a key role in this as a versatile energy carrier.

In the case of electricity and heat generation, decentralized generation without the emission of greenhouse gases will become much more important than it has been so far. Combined heat and power plants (CHP) operated with H₂, will be used on a large scale.

Lowest greenhouse gas emissions along with new regulation worldwide such as US Omnibus, European VII/7 and Bharat Stage CEV/Trem V point the way forward for all future combustion engines applications to emit lowest NO_X levels at all working conditions.

Historically, in addition to specific heat modes and change of combustion process to address robust emission control, lowest CO₂ target has been “decoupled” from exhaust aftertreatment emission control.

Meanwhile, advanced powertrain architectures such as hybrid technology and applications with electrical storage/energy recovery capabilities are opening up new system innovations for lowering CO₂ emissions combined with close coupled system architectures.

Thermal management technologies such as the proven Electrically Heated Catalyst (EHC) and the newly developed Electrically Heated Disc (EHD), which enable Exhaust Gas Aftertreatment System (EATS) to be heated with highly dynamic profiles, allow emissions regulation compliance with minimum CO₂ penalty over a wide working range.

This paper shows real-life examples of EHC-EHD systems with modular building blocks both for on-road and off-road applications, demonstrating the high level of integration with reduced impact on existing EATS architectures for global applications.

Off-highway tail pipe emissions have been regulated since 1997, targeting raw emission species like NOx, HC, PM and CO. Multiple amendments have been introduced, from Stage I till current regulatory norm of Stage V [1^st January 2017]. With Stage V, we already have achieved >95% NOx reduction [engine to tailpipe]. The next regulatory stage [beyond Stage V], is expected to have conversion efficiency of >90% from the Stage V limits of 0.4 g/kWh NOx tailpipe. (EUROPEAN COMMISSION, 2023)

With Stage V and Tier4f experience, the off-highway fraternity has developed the expertise to optimize the powertrain from engine till tailpipe to achieve stringent emission targets. While the technologies are available to meet ultra-Low NOx targets of future, identifying the right combination and to have a system approach is critical to keep the end-product effective, considering performance, robustness, and cost competitiveness.

Donaldson, as an aftertreatment system integrator, focusses on effective thermal management & efficient mixing technology to support meeting the ultra-Low NOx targets of future. This paper explains some of our validated concepts from child part level to support effective thermal management across EAT system. The primary focus is thermal retention, avoid heat losses, address cold start, and effectively support quick light off, of the oxidation catalyst & the SCR system. We will brief about the thermal CAE indications, and bench trials conducted on different technologies and their compounded benefits, supporting early SCR light off. These concepts are part of Donaldson’s “Readiness for Beyond Stage V” demonstrator work package, concentrated to add value to our customers and to support them in identifying the benefits of available technologies in market to achieve the ultra-Low NOx targets.

The latest proposals by CARB (California Air Resources Board) for Tier 5 legislation forecast significant tightening of pollutant emissions e.g., NO_x while also extending testing conditions, leading to exceptional challenges in powertrain development. In addition, the discussed reduction of CO₂ emissions enforces a continuous reduction in fuel consumption. For this purpose, an optimal calibration of engine-based thermal management in combination with an advanced EAT (Emission After Treatment) layout are key technologies. Furthermore, cold start and testing with low load cycles may also require external EAT heating measures.

In this study, a systematic investigation is carried out by means of a model-based holistic approach, targeting an EAT layout definition and optimal thermal management calibration to comply. A close-coupled dual-stage SCR (Selective Catalytic Reduction) with twin dosing is considered to minimize the fuel penalty during heat up phases. An optimization of the engine hardware concept and the engine thermal management is carried out and the potentials regarding CO₂ emissions are quantified.

This study shows that the proposed emission limits can be reached with a dual-stage SCR system. Implementing a keep-warm operation mode for low-load operation also paves the way for reaching NO_x-limits within the new Low Load Application Cycle (LLAC).

Recently the European Union (EU) has declared ambitious targets for CO₂ emission reduction in the heavy-duty vehicle segment. The published decarbonization strategy considers a reduction of CO₂ emissions by 90% until the year 2040. Intermediate steps foresee a reduction percentage of 45% by 2030 and 65% by 2035. Recently these targets are increased further to 100% in 2040, 95% in 2035 and 65% in 2030.

Due to the need to develop CO₂-emission free propulsion technologies also for the commercial vehicle sector the hydrogen internal combustion engine (H₂-ICE) technology is getting increased attention in the automotive industry. Currently, various manufacturers around the world are looking into the development of H₂-ICE based propulsion concepts.

The spark ignited H₂ combustion process itself does produce almost no species/pollutants which are currently in scope of different emission regulations if a specifical air to fuel ratio is maintained. However, during transient operation, a drop in air to fuel ratio can lead to high levels of NO_x formation requiring post-treatment technologies (SCR) to comply with current and upcoming regulations such as Euro 7 and Carb MY27.

In this article possible aftertreatment concepts for a H₂-ICE are described for different legislation scenarios.

Additionally, R&D results of an actual H₂-ICE equipped with an aftertreatment system configured specifically for the exhaust gas composition of a H₂-ICE are discussed. The system was tested in representative testbed test protocols as for example the WHTC cold and hot. Legally regulated gaseous emission species and PN10 were measured upstream and downstream of the exhaust aftertreatment systems (EAS).

This publication provides an insight into the development of an electric drive for mobile work drives. The development of the E-Deutz system stringently follows the V-process, which has already been established for years in software development. Using many examples from the E-Deutz system, the process is explained, and the system is presented at the same time. As the process itself, results from various tests on the system test bench are presented and explained. A special focus is given to functional safety based on ISO 26262, according to which the development process has recently been conform-certified, and the product will be certified by the end of the year 2023.

The electrification of mild- and heavy-duty vehicles sets highest demands on the traction motor. For example, the vehicle lifetime is multiple times higher as it is for passenger car applications and in addition, the ratio between continuous and peak power is much higher.

While state-of-the-art water jacket cooling concepts for electric motors are enabling a high peak power density, they are very limited with respect to continuous power density. This leads to large and heavy traction motors for mild- and heavy-duty applications.

MAHLE has developed the novel and innovative Superior Continuous Torque (SCT) electric motor cooling technology, which makes is possible to achieve much higher continuous power for a given package. The MAHLE SCT motor works with high continuous power output close to its peak power for an unlimited time. Within the motor, the oil is guided as close as possible to the source of the heat and at the same time mechanical losses caused by the oil are reduced to a minimum.

With its capability for a very long lifetime, highest continuous power density and efficiency, as well as suitable torque and speed characteristics, the SCT motor has been specifically designed to meet the requirements for mild- and heavy-duty applications. To find the best solution for each customer, MAHLE benefits from its core competence in the fields of thermal management, mechanical and electromagnetic design. MAHLE has developed a design workflow for electric machines, which makes a simultaneous multi-objective optimization of electromagnetic, mechanical, and thermal design possible.

Conventional wheel loaders are characterized by a hydraulic working system and a hydraulic propulsion system to move the machine. These systems share the same engine shaft power. There are several ways to hybridize the powertrain of a wheel loader, depending on the topology and number of electric machines used. For example, a parallel-series hybrid powertrain decouples the working hydraulics from its propulsion system, allowing both subsystems to be controlled independently. This could lead to significantly better system efficiency and simpler operation.

In this context, this paper presents a parallel-series hybrid powertrain concept and an adapted operating strategy for this system. The proposed operating strategy calculates the required minimum speed of the hydraulic pump based on the operator’s input and optimizes engine operating points to reduce fuel consumption while meeting other requirements such as propulsion torque and battery state of charge (SOC). A 7-ton wheel loader demonstrator vehicle was designed and built based on the proposed powertrain concept and operator interface. An adapted hybrid powertrain simulation model and the proposed operating strategy were validated using measured data obtained with the demonstrator vehicle. The simulations and field test results show a fuel consumption advantage of up to 30% compared to the conventional powertrain. The results are analyzed and the impact of the improved system efficiency on key requirements of future engine concepts is discussed.

At present, heavy-duty vehicles with long range and or high-performance requirements account for by far the largest proportion of CO₂ emissions in the transport sector. For this application, the Hydrogen Internal Combustion Engine (H₂ ICE) offers a promising addition to fuel cells for CO₂-free transport.

The aim of this paper is to further present the MAHLE H₂ research engine and the potential improvements and solutions that can be achieved by optimizing the engine power cell unit (PCU), covering key challenges of an H₂ fuelled ICE and its impact on lube oil consumption and blow-by.

The study considers the results of real-time thermal load of the pistons and cylinder walls using H₂-combustion measurements as input data for the components simulation model calibration. The model considers the complete oil transport by checking PCU dynamics, structural and lubrication analysis. Furthermore, material solutions known from gaseous fuels, as well as hydrogen-specific studies to cope with dry tribological conditions, were part of the requirements considered when selecting the component materials.

To test and validate the simulated models, a state-of-the-art 12.8 l diesel HD engine was converted to hydrogen and commissioned on a MAHLE test bench. Through a European Stationary-Cycle (ESC), tests were performed by continuously measuring the engine performance focusing on exhaust gases, blow-by, oil emission and oil consumption.

The paper concludes with a review of the key engine component results and their application to a heavy-duty hydrogen SI engine. These provide an additional basis for future developments with alternative fuels such as hydrogen, which offers a promising CO₂-neutral solution for the transport sector.

The forthcoming EURO-7 legislation, along with its strict NOx emission limits and further reduction of CO₂ fleet target values, requires additional development steps, especially for heavy-duty Diesel. To cope with these new challenges, the exhaust gas temperature management will play a pivotal role. Facilitating short warm-up phases of the exhaust gas after treatment system, as well as keeping engine-out emissions at a minimum will be part of the major engineering tasks in the heavy-duty Diesel engine sector. In addition, unwanted cool-down of the exhaust after treatment system during the drive cycles needs to be avoided. In low load conditions, in particular, this conflicts with the need to minimize CO₂ emissions.

Against this background, Schaeffler investigated the potential of fully variable valve lift & timing on a heavy-duty in-line six-cylinder engine, in comparison to alternative concepts like exhaust cam phasing or electrical catalyst heating.

In addition, the study assesses the potential of Schaeffler’s valve train solutions to support Zero-Impact engine concepts, including a virtual transition of a state-of-the art heavy-duty Diesel engine to a hydrogen powered SI engine.

The study suggests that fully variable intake valve train systems are an effective tool to meet future highly challenging emission targets and efficiency goals for ICEs. Moreover, adding flexibility to the exhaust valve timing paves the way for additional features like cylinder deactivation and compression release brake mode.

The transportation industry has set important objectives to reduce green-house gas emissions. Among alternative energy sources, hydrogen produced from low carbon pathways has been intensively studied within the industry and supported by public policies. Hydrogen fueled internal combustion engines can represent an interesting and complementary solution to power transportation and Off-Road equipment as well as accelerate the transition towards sustainable mobility.

On the one hand, hydrogen combustion properties offer the possibility to adjust internal combustion performance and meet technical and regulatory requirements expected by the market. On the other hand, the same combustion properties are raising important questions on the lubrication system requirements to ensure a reliable and efficient operation of hydrogen fueled internal combustion engines in the field.

This paper investigates the challenges associated with hydrogen internal combustion engine lubricant with regards to specific calibration features and application targets. Specific focus is given on the impact of hydrogen combustion on engine lubricant performance as well as impact of the lubricant features on engine performance. Higher power density, and exhaust gas emissions related to the lubricant are specifically targeted by this study.

Several formulation “levers” have been investigated and tested on a H₂ ICE on test bench. In particular, the influence of different lubricant formulations on the following parameters have been studied: behavior of the lubricant in contact with hydrogen; particulate emissions caused by the lubricant; influence of the lubricant on the pre-ignition phenomenon.

Experimental tests results are discussed to emphasize the importance of engine oil requirements, and the ability of the lubricant to support the development of hydrogen internal combustion engines.

Global decarbonization necessitates the use of sophisticated technologies to take the current internal combustion engine (ICE) to the next level. One approach is burning green hydrogen (H₂) and having engine power density and efficiency comparable to those of advanced Diesel engines (i.e., “diesel-like performance”) but with zero emissions. Achieving this objective requires burning H₂ at ultra-lean conditions preventing high thermal load on in-cylinder components and enabling reliable, durable, and cost effective solutions. This scenario has created the motivation to develop new technologies in the areas of hydrogen prechamber combustion, ignition and fuel injection, defining a holistic solution. In particular, the prechamber must operate with very lean lambda to prevent preignition and the ignition system must be able to deliver an adaptive spark energy/power that assures proper ignition of the ultra-lean hydrogen mixture while preventing the formation of hot spots on the electrodes leading to combustion instabilities like backfire, knock and preignition. Similarly, the hydrogen injection & mixing system must prevent the formation of rich pockets resulting in combustion abnormalities caused by lube oil preignition (LOP). This paper illustrates the performance potential of hydrogen engine combustion enabled by a holistic combustion solution and confirmed with engine test results. Moreover, the need for an Advanced Turbocharging System together with a Staged Development Approach are discussed for mitigating the technical and commercial risks associated with the introduction of competitive hydrogen engine technology in the market.

There is worldwide attempt to reduce both NOx and CO₂ emissions of Diesel vehicles. A common way to reduce CO₂ is via increasing engine fuel economy. This yields higher NOx emission from engine, in turn requiring higher rates of urea (AdBlue^™) injection for more efficient NOx reduction in the SCR catalyst. But more urea injection also increases the risk of forming urea deposits. In this work, we discuss using an Electrically Heated Mixer (EHM^™) to mitigate deposit risks while injecting varying amounts of urea, including high injection rates. Testing was conducted on a 5.2 lit. engine, demonstrating a pathway to meet MY2027 GHG phase-2 regulation with changes primarily in the controls and calibration strategies. CO₂ reduction strategy included engine down-speeding and increased EO-NOx. This required higher urea dosing during cold start conditions and lower exhaust temperatures during hot start, in turn increasing the challenges involved in achieving the MY2027 ultra-low NOx regulation 0.02 g/hp-hr (0.027 g/kW-hr). The EHM^™ evaluated in this study enabled dosing high urea dosing quantities to achieve NOx conversion efficiency without concerns for deposit. Urea injection rate varied by 6.5-fold, from 93 to 600 g/h (26 to 167 mg/s). It is shown that EHM effectively hinders urea deposit risks, yielding near-zero deposits.

Hydrogen as a fuel for internal combustion engines (ICE) is seen as an alternative way to conquer the threat of climate warming in the transport sector. With its broad range of ignition behavior and its very fast burn rate it offers some good potential as well. Currently this fuel in a gas phase is handled compared to CH₄ in gas engine looking on storage and ignition system—with adaptation in flow rates and leak tightness. Whether hydrogen is injected indirectly to the intake system whether directly to the combustion cell there are at least two problems caused by that fuel. In the first step hydrogen gets via piston, cylinder and piston rings into the crank case and forms concentrations likely to cause ignition in the crank case (lambda < 10). In the second step in combustion of hydrogens comes with a far higher water concentration in the exhaust gas, which will get into the crankcase as well and where it can leave the gas phase forming liquid water touching the oil in the engine—higher water content than permissible.

Hengst has proven in the past, for the use in passenger car vehicle, that an active crank case ventilation system can be a possibility to solve this problem. The ability to convey gas out of the crankcase with an electrically driven system offers the ability to activate an aeration of the crankcase air to dilute the natural blow by flow with fresh air and by this to minder the concentration of hydrogen in the crankcase atmosphere. The dilution can be done with a critical nozzle in combination with a check valve function, which is adapted to the Hengst Blue.tron system and to the engine itself. The fresh air flushing through the crank case can not only drive down the concentration of hydrogen but can also catch the water in the expanding atmosphere.

Engine dyno tests with a combination of Hengst disc separators and Hengst aeration valves proves the behavior on hydrogen use. Engines of different sizes—coming from passenger size up to heavy duty commercial vehicle size—are currently tested for the behavior about active separation and aeration of the crank case. Hydrogen as well as water content have been lowered towards lower temperatures and towards higher loads.

Hydrogen has been identified as a promising decarbonization fuel in internal combustion engine (ICE) applications in many areas including heavy-duty on and off road, power-generation, marine, etc. Hydrogen ICEs can achieve high power density and very low tailpipe emissions. However, there are challenges; designing systems for a gaseous fuel with its own specific mixing, burn rate and combustion control needs, which can differ from legacy products. Characterization and elimination of hot spots within the combustion are key to preventing unwanted pre-ignition.

The primary pollutant of concern for Hydrogen ICEs is NOX and this can be addressed by running the engine at very lean equivalence ratios and the use of Exhaust Gas Recirculation (EGR). Computation Fluid Dynamics (CFD) is a valuable tool to model the combustion characteristics under different conditions and can also be used to predict thermal loading.

Being able to determine thermal distribution and temperatures of the power cylinder components has always been critical to the design and development of ICE programmes. This remains a key requirement when considering hydrogen as an alternative fuel for both clean sheet hydrogen ICE designs and implementation of fuel conversions. Significant improvements have been made in recent years in the speed and accuracy of CFD tools for combustion and thermal prediction, but these still present lead times that can preclude their use in early concept work or parametric studies.

A recently developed thermal Finite Element (FE) tool helps to reduce CFD and thermal survey costs, complementing these approaches to make the engine development cycle more efficient. This new FE based tool meets the current and future challenges of ICE design and development, to accurately predict the thermal loading and temperatures of an ICE quickly under multiple full-load and part-load conditions, relevant for hydrogen combustion development.

This paper presents how both CFD and the FE analytical tools are applied to a Euro VI HD engine converted to operate on hydrogen gas using direct injection. A CFD model is presented that accurately predicts the trends in engine performance and correctly captures the flame acceleration driven by thermo-diffusive effects. In addition, CFD combustion and FE temperature results are presented at low-, part and full-load conditions including a lambda swing to investigate the effect of different equivalence ratios on structural temperature. These data are compared with measurements taken from a single-cylinder engine tested at the Ricardo hydrogen test facility.

DEUTZ is heading forward with the development of the TCG 7.8 H2, a Hydrogen Internal Combustion Engine (HICE) with a displacement of 7.8 liters. An upcoming application will be an HICE-powered hydraulic excavator, which will be developed within a funded project to demonstrate a CO₂-neutral construction site. The project is carried out in cooperation with University of Rostock and further partners.

With hydraulically driven applications one of the main requirements for good drivability is high dynamic load response and stable combustion with good homogenization. With this intent, several studies have been carried out on a single-cylinder engine (SCE) at the University of Rostock which supports the combustion relevant hardware definition and calibration strategy of TCG 7.8 H₂ at DEUTZ. Within the paper a brief overview of the ongoing HICE development activities in the funded project H2-MAM (H₂ engine for mobile working machines) will be given. Results from SCE and TCG 7.8 H₂ investigation will be shown, and calibration guide lines will be defined based on investigation results. Finally, an outlook of ongoing activities in the H₂-MAM project will be given.

For the new E38 MAN stationary gas engine series, the development goal from the very beginning was low-NO_x capability combined with market-leading characteristics in terms of mechanical efficiency and power density. Another premise was that the cast part of the diesel cylinder head of the new engine series had to be carried over for the gas application. To achieve these goals, simulations and bench tests went hand in hand: Through extensive studies in 1D CFD simulation, the feasibility limits in terms of mean effective pressure with at the same time low end-of-compression cylinder temperatures were determined using appropriate valve timings and a high compression ratio of the single stage turbo charger. The interaction of the valve timings with the different piston bowl shapes was investigated in the 3D CFD simulation, so that the test campaign on the single-cylinder test bench could be significantly reduced. Atkinson timings (LIVC—late intake valve closing) combined with a squish piston contour proved to be particularly attractive overall, as they allowed a high level of turbulent kinetic energy to be maintained over the entire compression and duty cycle. Further fine-tuning of the turbo charger matching, final optimization of the passive pre-chamber spark plug design and the application for different operating points was carried out on the multi-cylinder-engine. The final engine design enables a compact combustion at low raw NO_x emissions and a moderate heat dissipation from the combustion chamber. This results in best in class efficiencies and a superb mean effective pressure.