FINLAND LOOKS TO DEVELOP DUAL-FUEL RCCI ENGINE TECHNOLOGY

Maciej Mikulski, Associate Professor of Combustion Engine Technology (credit: Riikka Kalmi, University of Vaasa)
Maciej Mikulski, Associate Professor of Combustion Engine Technology (credit: Riikka Kalmi, University of Vaasa)
A Wärtsilä test engine at the University of Vaasa VEBIC energy lab (credit: Riikka Kalmi/University of Vaasa)
A Wärtsilä test engine at the University of Vaasa VEBIC energy lab (credit: Riikka Kalmi/University of Vaasa)
Industry Database

The upcoming Clean Propulsion Technologies project aims to develop flexible fuel solutions based on Reactivity Controlled Compression Ignition (RCCI), advanced aftertreatment and hybridization technology for fast and medium-speed combustion engines.

The two-year project will give Finland a leading position in low-carbon technology for shipping, off-road vehicles and stationary power applications. It will be led by Maciej Mikulski, Associate Professor of Combustion Engine Technology, and operationally managed by Merja Kangasjärvi, both from Finland’s University of Vaasa. It is expected to commence in Q1 this year if further funding is secured from Business Finland.

The project originates from the CleanShip co-creation project which brought together a consortium of six universities and research organizations (University of Vaasa, Tampere University, Aalto University, Åbo Akademi University, VTT Technical Research Centre of Finland and Lappeenranta-Lahti University of Technology LUT), nine companies (Wärtsilä Finland, AGCO Power, Dinex Finland, Proventia, Bosch Rexroth, Geyser Batteries, APUGenius, Napa and Meyer Turku) and four international partners.

“The common goal is to secure the global technology leader position for the Finnish powertrain industry by creating a common vision and sustainable business solutions,” says Mikulski. “The reason that marine and off-road propulsion manufacturers can work efficiently together on this project is that both sectors are currently facing dramatic change in tightening GHG and emissions legislation.”

Roadmap for 2030

A technology map has been prepared for technical solutions targeting 2030 emissions goals, and the key research streams are:

  • Develop new intelligent machine learning algorithms for virtual sensors, digital twins and control technologies (for use by the subsequent research streams)
  • By combining engine and after-treatment measures, demonstrate a minimum 20% reduction in GHG emissions and ultra-low NOx and particulate matter emissions
  • Design and implement an optimal control architecture for a hybrid system including batteries which will account for the characteristics of different energy and power sources
  • Build full-scale hybrid demonstrators of propulsion systems, targeting at least a 30% reduction in GHG emissions.

“This project shifts the paradigm from the time and resource consuming incremental improvement method used in earlier projects in favour of fast-tracking completely new systems by the use predictive simulation models,” says Mikulski. “The challenge is the calibration time of the new systems that need to be developed.” To realise the project’s objectives then, physics-based models, 3D CFD simulations and optical engine studies will be used to fast-track the dual-fuel low-temperature combustion RCCI engine technology which he anticipates will increase engine efficiency by 2% and reduce methane slip by 90% compared to current dual-fuel LNG engine technologies. Further progress towards near zero emissions will be achieved through advanced after-treatment and hybridization technologies developed in the project.

A holistic view of the project’s power train solutions will be complemented by route planning algorithms for operating conditions with large uncertainties, using ship-level simulations for the marine modelling. Together with sustainable fuels, these technologies form a promising short-term solution for decarbonization of energy production and heavy transport while satisfying future emission legislation, says Mikulski.

RCCI Research

RCCI technology was originally developed at the University of Wisconsin-Madison Engine Research Center laboratories. It is a variant of Homogeneous Charge Compression Ignition (HCCI) that uses in-cylinder fuel blending by first injecting a low reactivity fuel such as natural gas, methanol or hydrogen combined with air and recirculated exhaust gases followed by injection of a high reactivity fuel such as biodiesel directly into the combustion chamber.

Recent research by Mikulski and a team from the University of Vaasa and Lublin University of Technology has led to the development of the concept of using part of the engine cycle to act as a poly-generation reactor altering the reactivity and thermal state of the fuel-air mixture on a cycle-to-cycle basis. The research, published in Applied Energy, indicates that using natural gas as the low reactivity fuel results in high knock-resistance and a reduction in nitrogen oxides emissions, particulate matter and carbon dioxide emissions. However, this leads to relatively low combustion efficiency at low engine loads, causing unacceptable methane slip.

The researchers used numerical simulations to show that the application of negative valve overlap would resolve the issues by varying the timing and amount of fuel injected directly into the recompressed hot exhaust gases while simultaneously controlling for pressure rise. This on-demand reactivity allowed efficient low-temperature HCCI-like combustion to be maintained across the whole range of engine loads.

Further research showed that two key variables are crucial for closed-loop control: the crank angle of 50% fuel burnt and the combustion duration. These variables are closely coupled and can be calculated in real-time using well-established algorithms, making their management feasible.

Almost 99% combustion efficiency and ultra-low methane emissions were achieved under optimal conditions. Net indicated efficiency was 40.5% at 15% load. Low-load net efficiency was 5.5% above the lean strategy baseline and 3% better than the exhaust gas recirculation baseline simulations. The required pressure rise rate control can be achieved by supervisory control despite the negative valve overlap’s substantial pumping losses, and the researchers formulated a workable strategy to manage this based on trade-offs between pressure rise rate and efficiency and emissions.

Advanced Engine Control

As the research explained the mechanisms of improved combustion efficiency and translated them into control strategies, it bridges the gap between fundamental research on RCCI/HCCI and its industrial application and indicates that the technology can be successfully implemented in next-generation marine and power plant engines to reduce methane slip and sensitivity to fuel quality. The overall concept is based on new, yet proven, engine components, and it accommodates the latest advantages in combustion control, says Mikulski.

Thus, engines operating in RCCI combustion mode will require extensive use of advanced engine hardware such as waste gate - controlled multi-stage turbochargers, fully variable electro-hydraulic valve actuation, exhaust gas recirculation, proportionally controlled charge air coolers and multi-pulse injection capability. “Most of the challenges related to this new combustion system relate to controllability and calibration time,” says Mikulski. “This roughly doubles the number of parameters that need to be controlled independently and calibrated compared to a traditional combustion engine. Model-based development makes this leap possible where incremental development would otherwise make it unobtainable. The development includes cutting edge control protocols necessary for robust RCCI engine operation.”

In the high-speed (off-road) engine domain, two technologies (aside from advanced after-treatment and novel fuels that will also be developed as part of the project) form a short-term solution for reaching ultra-low emissions at superior efficiency, he says. The first is advanced engine hardware like variable valve actuation in combination with cylinder deactivation. This enables efficient engine thermal management to support after-treatment systems in reaching their peak efficiency. This will be explored experimentally and by simulations.

The second technology is related to advanced engine cycles. “The split cycle engine concept - where separate cylinders realize compression and expand the combusted mixture - is another radical idea offering a step-change efficiency increase combined with higher power density,” says Mikulski.

Fuel Choices

Natural gas, biogas methanol will be fuels focused on in the project, along with a biogas/hydrogen mix. “These fuels are considered short-term low carbon transition fuels for shipping instantly reducing engine-out CO2 emissions by approximately 25%,” Mikulski says. “For both fuels, (L)NG and methanol, the worldwide bunkering infra is already majorly developed and IMO Stage II/ III engine technology is already there. Energy density satisfies the need of long-haul sea transport, and both fuels have similar, efficient routes towards full sustainability with CO2 capture/hydrogen synthesis and already now biogas and hydrogen can be, and are, added to natural gas to make it more sustainable. The use of (L)NG, in particular, is expected to scale up rapidly in the marine domain – we thus need future proof solutions to support this transition.”

Future Challenges

The use of 100% hydrogen will be considered. The Clean Propulsion Technologies project will build a high-speed off-road demonstrator engine for this, while another project the University of Vaasa is leading, CHEK, will scale it up for use in the marine domain.  “The technological readiness of the 100% hydrogen solution in the Clean Propulsion Technologies will be rather low. We will show that we can do it, yet without particular targets in terms of emission conformity and efficiency, the initial-step ambition, in our opinion, fits into the current infrastructural maturity of the 100% hydrogen as fuel concept.”

While the roadmap for the project is developed for 2030, there is still uncertainty beyond that, and therefore more mapping work required once the project focuses on 2050 emissions reduction targets. According to Mikulski, the current energy transition is a big challenge, but also a big opportunity for further research. “To meet the challenge and seize the opportunity, broad community support is necessary, and various stakeholders need to start working together on a common and unbiased vision. In Finland we have taken an important step towards this success.”

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