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New integrated combustion system for future passenger car engines (NICE)

Final Report Summary - NICE (New Integrated Combustion System for future Passenger Car Engines)

The overall objective of the NICE project consisted in the development of different integrated combustion systems (now in plural), for different types of fuel (gasoline, diesel, compressed natural gas, synthetic biomass-based fuels), which are able to achieve the excellent fuel conversion efficiency of a cutting-edge DI diesel engine while complying with very low future emission levels (i.e. in the mean time, EU6).

At the beginning, the vision of the NICE project was one single combustion system at the horizon, to be reached in the subsequent framework programs 8 and 9, and it was expected that a convergence towards this single system would occur in the future. During the project, however, this vision has changed: now, it is mainly assumed, that there will possibly be a convergence concerning several components and technologies like turbo-charging or direct injection, but a total fusion within one single concept will not occur. In contrary, future could become even more various. According to this scenario, even the number of different gasoline and diesel engine concepts would increase, depending on local markets incl. local legislation and incentive politics. Furthermore, new fuels get onto the scene, natural gas being only one of them, but also several biogenic fuels could arise.

The concrete objective had to be specified according to the type of fuel:
- For a gasoline engine, improving fuel economy while keeping low emission levels is the major goal. This may be achieved by introducing new technology components like direct injection, downsizing by turbo-charging and variable valve train.
- For diesel engines, an important and challenging task consists in improving the emission levels (towards EU6) with no loss in fuel economy when compared to a current EU4 engine, at affordable cost increase.
- CNG (compressed natural gas) engines already exhibit very low CO2 emission levels. Besides further reducing fuel consumption, a major task consists in making such engines more attractive by modern engine technologies (e.g. turbocharging) in order to enable an increased market share of such engine concepts.
- Biofuels made from renewable biomass are already an efficient mean for reducing CO2 emissions. Second generation biofuels, however, offer additional potentials by designing dedicated engines for tailored biofuels. These potentials can be used in order to improve fuel economy as well as to reduce system cost (f.i. after-treatment), especially when applied for fulfilling EU6 emission standards in a diesel-like combustion process.In order to address these topics, the NICE project consisted of four sub-projects:

- A1: Enlarged HCCI (Homogeneous charge compression ignition) diesel combustion process under transient operation (OEM: Renault).
Subproject A1 addressed enlarged HCCI diesel combustion. The purpose is to improve the emission levels of a diesel engine toward EU6 with no loss in fuel economy compared to a EU4 current engine. Cost increase must stay reasonable hence the technical solutions have been chosen to avoid using costly NOx after treatment. A wide range of work has been carried out from better understanding the combustion with numerical, optical and dedicated testing facilities to the building and calibration of a demonstrator vehicle. As the final product, the vehicle is equipped with the selected technologies integrated in a multi-cylinder engine using HCCI combustion principle on a wide range of operation (at least NEDC cycle) and fully capable of being driven.

- A2: Compressed / spark ignited variable engines, including a new diesel-type combustion system for tailored biomass-based fuels (OEMs: Fiat, VW, Daimler)
The main general objectives of sub-project A2 have been:
a) the development of subsystems of integrated flexed low cost components with the goal of a variable ICE structure;
b) the definition of a combustion system able to run also on tailored bio/bio-blend fuels (to this purpose, liquid fuel specs have been investigated and proper recommendations for renewable fuels have been released);
c) the increase of the fuel conversion efficiency of about 10 % with particular regard of engines running on diesel fuel and gasoline that have the main impact on the environment in the next 20 - 30 years.
Sub-project A2 considered different approaches for different combustion processes:
a) spark ignited combustion process;
b) compression ignited combustion process.

- A3: Future CNG internal combustion engines (OEMs: Daimler, Ford)
Vehicles powered with natural gas are well known for a long time. However, today's gas engines for passenger cars and commercial vehicles still have the heavy drawback of being developed as multi-fuel engines on the basis of conventional internal combustion engines. Optimised mono-fuel natural gas engines offer additional potential regarding fuel consumption, emissions and performance. Objective of this subproject was to evaluate this potential and to find out favourable technological concepts.

During the initial concept phase a downsizing concept with high boost turbo-charging was chosen due to the high knock resistance of natural gas. Furthermore different technological approaches for mono-fuel turbocharged CNG engines have been generated:
- technology way 1: direct injection (DI), high rail pressure, stoichiometric / lean mixture combustion
- technology way 2a: port fuel injection (PFI), overall (part load / WOT) lean mixture combustion via the Advanced turbulence assisted combustion (ATAC) concept
- technology way 2b: port fuel injection (PFI), stoichiometric / lean mixture combustion.

- B1: Improved CFD (computational fluid dynamics) tools and modelling (OEMs: Volvo, Daimler, Renault, Volkswagen)
The work in subproject B1 was organised to provide a solution to some of the remaining critical issues in diesel combustion modelling with special focus on the novel engine solutions developed in NICE. Some models were simply not available prior to the project such as models to predict the long ignition delays at high EGR conditions typical for the new NICE combustion concepts and models for alternative/optimised fuels. In other areas as spray, mixing and basic combustion available models were further improved and adapted. All models were carefully validated and implemented in engine CFD codes resulting in useful simulation tools also for the development of novel combustion processes. In addition, the modelling of conventional engines has become more mature also including the capability to model soot formation with a sufficient degree of accuracy.

Concerning engine technology, there is not only one single path into future, but several ones. On the gasoline side, significant improvements concerning fuel economy are possible, especially by concepts based on turbo-charging plus downsizing. This combination is the major enabler. String downsizing from 2l => 1,4l may achieve up to 15 % reduction in fuel consumption. First downsizing concepts can already seen on the market, further ones will follow soon.

Turbo-charging, however, can not only be realised by a combination of a large turbocharger with a small engine, this would generate a strong turbolag. Downsizing has to be moderate, or it has to be supported by special turbo-charging agility concepts like DOT ('delay optimised turbocharger', concept in NICE A2). Other (more common) concepts which aim at a fast response turbo-charging are the variable turbine or two-stage turbo-charging. Increased agility of the turbocharger may also be supported by other technologies like gasoline direct injection or variable valve actuation (what has been done in NICE A2 by electro-hydraulic valve actuation; a large downsizing step was enabled).

Any further request on progress in fuel economy, however, cannot be fulfilled by moderate downsizing only. Consequently, in NICE, combinations with additional fuel economy technologies have been examined: turbo-charging / downsizing and variable valve actuation, turbo-charging / downsizing and direct injection / lean operation / lean NOx aftertreatment. With such technology packages, fuel economy advantages of 20 %, when compared to a state-ofthe- art gasoline engine and taking into account losses due to real after-treatment operation, seem to be reachable. Other options are advanced turbo-charging / strong down-sizing.

For diesel engines, however, the first task is to fulfil the challenging EU6 emission targets without increase in CO2 emissions. Technology concepts are not as varying as on gasoline side: advanced high-EGR concepts (including low-pressure EGR and residual gas retention), advanced turbo-charging concepts like two-stage turbo-charging, downsizing and advanced injection concepts (piezo-actuated, increased injection pressure). It can be concluded from NICE that, using these concepts, it may be possible to fulfil EU6 emission limits without NOx-aftertreatment and without deterioration in fuel consumption, with reference to state-ofthe- art EU4 engines, at least for smaller and medium-sized vehicles.

As impressive as the NICE results are, it has to be concluded that these concepts are not sufficient to fulfil the currently discussed CO2 emission demands in total.

It is important to point out the following:
- all gasoline engines would get a 'NICE' package, i.e. one of the following technology packages: turbo-charging / downsizing and variable valve actuation (phasing + lift); turbo-charging / downsizing and direct injection and lean NOx-aftertreatment; advanced turbo-charging / strong downsizing;
- this would lead to an average CO2 advantage of about -20 %, relatively to a state-of-the- art gasoline engine (including cam phasing);
- all diesel engines would get a 'NICE' package, i.e. a combination of advanced EGR, advanced turbo-charging / downsizing and advanced injection technologies, without any NOx after-treatment;
- this would be the enabler for fulfilling EU6 without deterioration in fuel economy.
As far as engine technology is concerned, the addition of further fuel economy components like variable compression ratio or NOx after-treatment for diesel engines or the creation of larger technology packages may result in a few additional percents of gain of fuel economy, at strongly increased cost. Since costs of different components do not only add up, even the increasing complexity of interaction will cause additional cost. Fuel economy increases at a much smaller rate, due to the fact that many fuel economy measures act in the same or at least a similar manner (one engine can be dethrottled only once). Therefore, a strong further increase in engine efficiency may only be achieved by an extremely expensive overall hybridisation roll-out.