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The present paper describes the first results of a cooperative research project between GM Powertrain Europe and Istituto Motori of CNR aimed at studying the impact of Fatty-Acid Methyl Esters (FAME) and gas-to-liquid (GTL) fuel blends on the performance, emissions and fuel consumption of modern automotive diesel engines. The tests were performed on the architecture of GM 1.9L Euro4 diesel engine for passenger car application, both on optical single-cylinder and on production four-cylinder engines, sharing the same combustion system configuration. Various blends of biodiesels as well as reference diesel fuel were tested. The experimental activity on the single-cylinder engine was devoted to an in-depth investigation of the combustion process and pollutant formation, by means of different optical diagnostics techniques, based on imaging multiwavelength spectroscopy.

The present paper describes some results of a cooperative research project between GM Powertrain Europe and Istituto Motori of CNR aimed at studying the impact of FAME and GTL fuel blends on the performance, emissions and fuel consumption of the latest-generation automotive diesel engines. The investigation was carried out on the newly released GM 2.0L 4-cylinder “torque-controlled” Euro 5 diesel engine for PC application and followed previous tests on its Euro 4 version, in order to track the interaction between the alternative fuels and the diesel engine, as the technology evolves. Various blends of first generation biodiesels (RME, SME) and GTL with a reference diesel fuel were tested, notably B20, B50 and B100. The tests were done in a wide range of engine operation points for the complete characterization of the biodiesels performance in the NEDC cycle, as well as in full load conditions.

The present paper describes some results of a research project aimed at studying the impact of alternative fuels blends on the emissions and fuel consumption of an Euro 5 automotive diesel engine. Two alternative fuels were chosen for the experiments: RME and GTL. The tests were done in the three most important operating conditions for the engine emission calibration. Moreover, the NOx-PM trade-off by means of EGR sweep was performed in the same operating conditions, in order to evaluate the engine EGR tolerability when burning low sooting fuels as the RME. The investigations put in evidence that the impact of the alternative fuels on modern diesel engines remains significant. This also depends on the interaction between the alternative fuel characteristics and the engine-management strategies, as described in detail in the paper.

Natural gas as an internal combustion engine fuel is taking a predominant role as a mid-term solution to pollution due to combustion driven human activities both in the energy and transport sectors. Engine researchers and manufacturers are in the process of investigating and improving strategies that decrease emissions and fuel consumption, without compromising engine performance and efficiency; active pre-chamber configurations are to be accounted for as one of these. A relatively small amount of fuel (up to 10 % of the total fuel-energy requirement) is introduced in the confined volume of the pre-chamber and forms a close-to-stoichiometric mixture with fresh charge that is introduced from the main combustion chamber during the compression stroke. After spark-ignition the products of this early stage of combustion can ignite ultra-lean mixtures (with λ up to 2) through the Turbulent Jet Ignition mechanism, hence reducing fuel consumption as well as noxious emissions such as NOx.

In the recent years, the interest in heavy-duty engines fueled with Compressed Natural Gas (CNG) is increasing due to the necessity to comply with the stringent CO2 limitation imposed by national and international regulations. Indeed, the reduced number of carbon atoms of the NG molecule allows to reduce the CO2 emissions compared to a conventional fuel. The possibility to produce synthetic methane from renewable energy sources, or bio-methane from agricultural biomass and/or animal waste, contributes to support the switch from conventional fuel to CNG. To drive the engine development and reduce the time-to-market, the employment of numerical analysis is mandatory. This requires a continuous improvement of the simulation models toward real predictive analyses able to reduce the experimental R&D efforts. In this framework, 1D numerical codes are fundamental tools for system design, energy management optimization, and so on.

Low temperature combustion (LTC), is a promising alternative for combustion engines, because it combines the positive aspects of both CI and SI engines, high efficiency and low emissions. Another positive aspect of LTC is that it can operate with gasoline of different octane ratings. Still, higher octane gasolines prove to be difficult to operate at low load conditions leading to high combustion instability (COV) that leads also to high emissions. This drawback can be reduced by increasing the intake air temperature or increasing compression ratio, but it is not a viable strategy in conventional applications. For a diesel engine running under LTC conditions, a possibility is to use the existing hardware, glow plugs in this case, to increase the in-cylinder temperature at low loads and facilitate an improved combustion event.

CO2 is a greenhouse gas that is believed to be one of the main contributors to global warming. Recent studies show that a combination of methanol as a renewable fuel and advanced combustion concepts could be a promising future solution to alleviate this problem. However, high unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions can be stated as the main drawback in low load operations when using methanol under advanced combustion concepts. This issue can be mitigated by modifying the stratification of the local equivalence ratio to achieve a favorable level. The stratifications evolved, and the regimes that can simultaneously produce low emissions, and high combustion efficiency can be identified by sweeping the injection timing from homogeneous charge compression ignition (HCCI) to partially premixed combustion (PPC). Understanding how the stratification of the local equivalence ratio for methanol evolves during the sweep is essential to gain these benefits.

Methanol is not a fuel typically used in compression ignition engines due to the high resistance to auto-ignition. However, conventional diesel combustion and PPC offer high engine efficiency along with low HC and CO emissions, albeit with the trade-off of increased NOx and PM emissions. This trade-off balance is mitigated in the case of methanol and other alcohol fuels, as they bring oxygen in the combustion chamber. Thus methanol compression ignition holds the potential for a clean and effective alternative fuel proposition. Most existing research on methanol is on SI engines and very little exists in the literature regarding methanol auto-ignition engine concepts. In this study, the spray characteristics of methanol inside the optically accessible cylinder of a DI-HD engine are investigated. The liquid penetration length at various injection timings is documented, ranging from typical PPC range down to conventional diesel combustion.

The focus has recently been directed towards the engine out soot from Diesel engines. Running an engine in PPC (Partially Premixed Combustion) mode has a proven tendency of reducing these emissions significantly. In addition to combustion strategy, several studies have suggested that using alcohol fuels aid in reducing soot emissions to ultra-low levels. This study analyzes and compares the characteristics of PM emissions from naphtha gasoline PPC, ethanol PPC, methanol PPC and methanol diffusion combustion in terms of soot mass concentration, number concentration and particle size distribution in a single cylinder Scania D13 engine, while varying the intake O2. Intake temperature and injection pressure sweeps were also conducted. The fuels emitting the highest mass concentration of particles (Micro Soot Sensor) were gasoline and methanol followed by ethanol. The two alcohols tested emitted nucleation mode particles only, whereas gasoline emitted accumulation mode particles as well.

Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings.

There is growing global interest in using renewable alcohols to reduce the greenhouse gases and the reliance on conventional fossil fuels. Recent studies show that methanol combined with partially premixed combustion provide clear performance and emission benefits compared to conventional diesel diffusion combustion. Nonetheless, high unburned hydrocarbon (HC) and carbon monoxide (CO) emissions can be stated as the main PPC drawback in light load condition when using high octane fuel such as Methanol with single injection strategy. Thus, the present experimental study has been carried out to investigate the influence of multiple injection strategies on the performance and emissions with methanol fuel in partially premixed combustion. Specifically, the main objective is to reduce HC, CO and simultaneously increase the gross indicated efficiency compared to single injection strategy.

Research activities in the development of reliable computational models for aftertreatment systems are constantly increasing in the automotive field. These investigations are essential in order to get a complete understanding of the main catalytic processes which clearly have a great impact on tailpipe emissions. In this work, a 1D chemical reaction model to simulate the catalytic activity of a Pd/Rh Three-Way Catalyst (TWC) for a Natural Gas heavy-duty engine is presented. An extensive database of tests carried out with the use of a Synthetic Gas Bench (SGB) has been collected to investigate the methane abatement pathways, linked to the lambda variation and oxide formation on palladium surface. Specific steady-state tests have shown a dynamics of the methane conversion even at fixed λ and temperature conditions, essentially due to the Pd/PdO ratio.

The present work relates to the investigation of the basic oxidation characteristics of iron and aluminium nanoparticles as well as the feasibility of their combustion under both Internal Combustion Engine (ICE)-like and real engine conditions. Based on a series of proof-of-concept experiments, combustion was found to be feasible taking place in a controllable way and bearing similarities to the respective case of conventional fuels. These studies were complimented by relevant in-situ and ex-situ/post-analysis, in order to elaborate the fundamental phenomena occurring during combustion as well as the extent and ‘quality’ of the process. The oxidation mechanisms of the two metallic fuels appear different and -as expected- the energy release during combustion of aluminium is significantly higher than that released in the case of iron.

The diesel particulate filters (DPF) are considered the most robust technologies for particle emission reduction both in terms of mass and number. On the other hand, the increase of the backpressure in the exhaust system due to the accumulation of the particles in the filter walls leads to an increase of the engine fuel consumption and engine power reduction. To limit the filter loading, and the backpressure, a periodical regeneration is needed. Because of the growing interest about particle emission both in terms of mass, number and size, it appears important to monitor the evolution of the particle mass and number concentrations and size distribution during the regeneration of the DPFs. For this matter, in the presented work the regeneration of a catalyzed filter was fully analyzed. Particular attention was dedicated to the dynamic evolution both of the thermodynamic parameters and particle emissions.

The present paper describes the results of a cooperative research project between GM Powertrain Europe and Istituto Motori - CNR aimed at studying the capability of GM Combustion Closed-Loop Control (CLCC) in enabling seamless operation with high biodiesel blending levels in a modern diesel engine for passenger car applications. As a matter of fact, fuelling modern electronically-controlled diesel engines with high blends of biodiesel leads to a performance reduction of about 12-15% at rated power and up to 30% in the low-end torque, while increasing significantly the engine-out NOx emissions. These effects are both due to the interaction of the biodiesel properties with the control logic of the electronic control unit, which is calibrated for diesel operation. However, as the authors previously demonstrated, if engine calibration is re-tuned for biodiesel fuelling, the above mentioned drawbacks can be compensated and the biodiesel environmental inner qualities can be fully deployed.

A wider use of biofuels in internal combustion engines could reduce the emissions of pollutants and greenhouse gases from the transport sector. In particular, due to stringent emission regulatory programs, compression ignition engine requires interventions aimed at reducing their polluting emissions. Ethanol, a low carbon fuel generally produced from biomass, is a promising alternative fuel applicable in compression ignition engines to reduce CO2 and soot emissions. In this paper, the application of a dual fuel diesel-ethanol configuration in a light-duty compression ignition engine has been numerically investigated. Ethanol is injected into the intake port, while diesel fuel is directly injected into the combustion chamber of the analyzed engine. CFD simulations have been carried out by means of the AVL Fire 3-D code. The operation at given engine load and speed has been simulated considering different diesel injection timings.

In the global scenario of encouraging the use of renewable sources, the bioethanol as fuel supply in the automotive sector is receiving increasing interest. In the present paper the results of a research activity aimed to study the impact of a bioethanol/biodiesel/mineral diesel blend on performance and emissions of an automotive diesel engine are reassumed. An experimental campaign has been devoted to characterize the engine fuelled by the ethanol based blend highlighting the advantages and issues related to the bioethanol use. Moreover, the effects of the most important injection settings on the engine performance have been detailed, applying a Design of Experiment (DoE) method, to identify the potentiality offered by a proper engine calibration to optimize the ethanol blend use.

Diesel engines are one of the most important power generating units these days. Increasing greenhouse gas emission level and the need for energy security has prompted increasing research into alternative fuels for diesel engines. Biodiesel is the most popular among the alternatives for diesel fuel as it is biodegradable and renewable and can be produced domestically from vegetable oils. In recent years, hydrotreated vegetable oil (HVO) has also gained popularity due to some of its advantages over biodiesel such as higher cetane number, lower deposit formation, storage stability, etc. HVO is a renewable, paraffinic biobased alternative fuel for diesel engines similar to biodiesel. Unlike biodiesel, the production process for HVO involves hydrogen as catalyst instead of methanol which removes oxygen content from vegetable oil.

The present paper describes the effects of some operating parameters on the performance of a single cylinder research engine when it runs under Low Temperature Combustion (LTC) conditions. Aim of the experimental work was to explore the potential of the control of each parameter on the improvement of LTC application to the modern LD diesel engines for passenger cars. In particular, the effects on LTC performance of the following operating parameters in different engine test points were analyzed: intake air temperature, exhaust EGR cooler temperature, intake pipe pressure, exhaust pipe pressure and swirl ratio. Some parameters have shown a particular influence on the improvement of EGR tolerability for maximum NOx reduction preserving fuel consumption and smoke, while others have evidenced poor sensitivity.

The present paper describes a detailed experimental analysis on the effect of the compression ratio on the performance of a single-cylinder research diesel engine operating with both conventional combustion and Low Temperature Combustion mode for low NOx emissions. The single-cylinder engine was developed with the same combustion system architecture of the four-cylinder FIAT 1.9 liter Multi-Jet. Starting from an engine configuration with a compression ratio of 16.5, the compression ratio was reduced to 14.5. For both the geometric configurations, engine performance was evaluated in terms of thermodynamic parameters, emissions and fuel consumption in some operating test points representative of the engine behavior running on the NEDC cycle.