Cold Start Conditions Research Articles

Ignition and combustion development for high speed direct injection diesel engines under low temperature cold start conditions

Diesel engine cold start is an important issue for current technology at low (below 0°C) temperatures and for future applications. The aim of this work is to develop a description of how, when and where does fuel spray ignition occur in a glow-plug assisted engine under simulated low temperature cold start conditions. In-cylinder pressure analysis is combined with high speed visualization in an optical engine. A pilot plus main injection strategy is used. Visualization results show that pilot ignition occurs in the vicinity of the glow plug, and strongly influences main combustion initiation. Main combustion starts from the pilot flame, and propagates to the rest of the combustion chamber showing a strong visible reaction zone. After end of main injection, the rapid leaning of the mixture suppresses the strong radiation, and OH radiation is observed to progress to the rest of the combustion chamber. The combustion process shows a strong scattering, which has been quantified by combustion parameters. At higher rail pressures scattering increases, which eventually inhibits combustion initiation. However, if ignition occurs at higher rail pressures, cycle performance is better.

The Application of Coconut-oil Methyl Ester for Diesel Engine

The cold start performance and ignition characteristics of coconut-oil methyl ester (CME) were investigated by using a diesel engine. Diesel fuel and CME were mixed and the blended ratio of CME was changed. The tests were conducted at full load and 3000 min-1. Diesel engine could be run stably with any mixing ratio of CME, however the power was slightly reduced with increasing CME mixing ratio. In cold start condition, when the mixing ratio of CME increased, the combustion chamber wall temperature rose quickly and the ignition timing was advanced. Therefore, CME had superior compression ignition characteristics in the cold start.

English

The population of spark-ignition vehicles in urban areas is very high and is increasing rapidly due to their convenience for short distance transportation. These vehicles are major sources of urban air pollution compared to vehicles with diesel engines. Catalytic converters are used to control their emissions but they attain their maximum conversion rates of about 80%–90% under optimum operating conditions and are not effective during cold start conditions. The objective of the present work is to demonstrate that an electrically heated catalyst (EHC) in combination with a traditional converter can achieve the Low and Ultra Low Emission Vehicle (LEV, ULEV) standards. Experiments were conducted to investigate the impact of various metal oxides in EHC and design parameters to reduce cold-start emissions of a multi-cylinder SI engine. It is observed that EHC reduces cold-start hydrocarbon and carbon monoxide emissions when used with an existing catalytic converter. The maximum CO and HC reductions were achieved with copper oxide as the catalyst in EHC with air injection of 80 lpm for 40 sec after cold start of the engine.

3-D Numerical Simulation and Experiment Study on the Wear of Piston Ring-Cylinder Liner

Aiming at a large marine diesel engine, a mathematical model for the 3-D elastohydrodynamic lubrication analysis of piston ring-cylinder liner was presented. The average Reynolds equation and asperity contact approach were combined with the elastic deformation equation. The asymmetry in the circumferential direction, gas blowby and the effect of temperature and pressure on the oil density and viscosity were considered. The 3-D wear simulation of piston ring-cylinder liner was performed when the diesel engine was operated under warm start and cold start conditions, respectively. The 3-D distribution rules show that the first gas ring has the biggest wear loss, and the maximum wear loss of cylinder liner occurs in the vicinity of TDCF. Finally, the results matched well with the wear measurements, and it indicates the present method is effective and can help engineers to improve the tribological performance of the diesel engine.

Oxidative Potential of Logwood and Pellet Burning Particles Assessed by a Novel Profluorescent Nitroxide Probe

This study reports the potential toxicological impact of particles produced during biomass combustion by an automatic pellet boiler and a traditional logwood stove under various combustion conditions using a novel profluorescent nitroxide probe, BPEAnit. This probe is weakly fluorescent but yields strong fluorescence emission upon radical trapping or redox activity. Samples were collected by bubbling aerosol through an impinger containing BPEAnit solution, followed by fluorescence measurement. The fluorescence of BPEAnit was measured for particles produced during various combustion phases: at the beginning of burning (cold start), stable combustion after refilling with the fuel (warm start), and poor burning conditions. For particles produced by the logwood stove under cold-start conditions, significantly higher amounts of reactive species per unit of particulate mass were observed compared to emissions produced during a warm start. In addition, sampling of logwood burning emissions after passing through a thermodenuder at 250 degrees C resulted in an 80-100% reduction of the fluorescence signal of the BPEAnit probe, indicating that the majority of reactive species were semivolatile. Moreover, the amount of reactive species showed a strong correlation with the amount of particulate organic material. This indicates the importance of semivolatile organics in particle-related toxicity. Particle emissions from the pellet boiler, although of similar mass concentration, were not observed to lead to an increase in fluorescence signal during any of the combustion phases.

The impact of soy-based biodiesel on PAH, nitro-PAH and oxy-PAH emissions from a passenger car operated over regulated and nonregulated driving cycles

This study explores the impact of neat soy-based methyl ester and its 50% v/v blend with low sulphur automotive diesel on PAH, nitro-PAH and oxy-PAH emissions of a Euro 2 compliant diesel passenger car tested on a chassis dynamometer. Emission measurements were evaluated for the certification NEDC, a hot-start UDC (urban part of NEDC) and the non-legislated Artemis driving cycles which simulate urban, rural and highway driving conditions in Europe. Overall, 16 PAHs, 4 nitro-PAHs and 6 oxy-PAHs were determined in the exhaust. The results obtained, showed that PAH emissions decreased with the addition of biodiesel during all driving modes. However, their nitrated and oxygenated products were found to increase with biodiesel compared to diesel fuel. The use of pure biodiesel led in some increases in PAH emissions when compared to its 50% blend. PAH emissions were also found to be adversely influenced by cold-start conditions and certain fuel properties.

Simulation of hydrogen and hydrogen-assisted propane ignition in pt catalyzed microchannel

This paper deals with self-ignition of catalytic microburners from ambient cold-start conditions. First, reaction kinetics for hydrogen combustion is validated with experimental results from the literature, followed by validation of a simplified pseudo-2D microburner model. The model is then used to study the self-ignition behavior of lean hydrogen/air mixtures in a Platinum-catalyzed microburner. Hydrogen combustion on Pt is a very fast reaction. During cold start ignition, hydrogen conversion reaches 100% within the first few seconds and the reactor dynamics are governed by the “thermal inertia” of the microburner wall structure. The self-ignition property of hydrogen can be used to provide the energy required for propane ignition. Two different modes of hydrogen-assisted propane ignition are considered: co-feed mode, where the microburner inlet consists of premixed hydrogen/propane/air mixtures; and sequential feed mode, where the inlet feed is switched from hydrogen/air to propane/air mixtures after the microburner reaches propane ignition temperature. We show that hydrogen-assisted ignition is equivalent to selectively preheating the inlet section of the microburner. The time to reach steady state is lower at higher equivalence ratio, lower wall thermal conductivity, and higher inlet velocity for both the ignition modes. The ignition times and propane emissions are compared. Although the sequential feed mode requires slightly higher amount of hydrogen, the propane emissions are at least an order of magnitude lower than the other ignition modes.

A Method to Determine Fuel Transport Dynamics Model Parameters in Port Fuel Injected Gasoline Engines During Cold Start and Warm-Up Conditions

In order to meet stringent emission standards, it is essential to have a precise control of air-fuel ratio (AFR) under cold start and warm-up conditions. This requires an understanding of the fuel transport dynamics in the intake system during these conditions. This study centers on estimating the parameters of a fuel transport dynamics model during engine operation at different thermal conditions ranging from cold start to fully warmed-up conditions. A method of system identification based on perturbing fuel injection rate is used to find fuel dynamics parameters in a port fuel injected (PFI) spark ignition engine. Since there was no cold chamber available to prepare cold start conditions, a new method was utilized to simulate cold start conditions. The new method can be applied on PFI engines, which use closed valve injection timing. A four-cylinder PFI engine is tested for different thermal conditions from −15°C to 82°C at a range of engine speeds and intake manifold pressures. A good agreement is observed between simulated and experimental AFR for 52 different transient operating conditions presented in this study. Results indicate that both fuel film deposit factor (X) and fuel film evaporation time constant (τf) decrease with increasing coolant temperature or engine speed. In addition, an increase in the intake manifold pressure results in an increase in X while causes a decrease in τf.

Fabrication and testing of Al–SiCp composite poppet valve guides

Composite materials are replacing the materials used in various fields and are the candidate materials for future growth. Metal matrix composites are the class of composite materials finding vast applications in automotive, aircraft, defense, sports, and appliance industries. In the present work, Al–SiCp composites with 5–30 wt.% of SiC particulates were fabricated using powder metallurgy as well as casting processes. Mechanical alloying of aluminum and SiC particles was done prior to compaction so as to enhance the properties of the fabricated powder metal components. A custom built sliding valve guide wear test rig was fabricated to simulate the valve stem/guide wear under cold start condition of an engine by reciprocation of a valve stem under different imposed loads, against a stationary poppet valve guide. The hardness and radial crushing load was measured for the Al–SiCp composite poppet valve guides and were found better than the cast iron poppet valve guides presently used in engines. The wear test of the poppet valve guides was done using valve guide wear test rig, which revealed that the Al-20 wt.% SiCp and Al-30 wt.% SiCp composite poppet valve guides have higher wear resistance than the cast iron poppet valve guides. The hardness, radial crushing load, and wear resistance of Al–SiCp composite poppet valve guides were found to increase with increase in weight percent of SiCp. The microstructural analysis of the cast and PM Al–SiCp composites was also done using scanning electron microscope. Finite element analysis of the Al–SiCp composite poppet valve guide was also done using Ansys software, which supports the successful implementation of the Al–SiCp composite poppet valve guides for automobiles.

Electrically Driven Redox Process in Cerium Oxides

Cerium oxides have attracted much attention because of their uses in three-way catalysts and other catalyst applications. The redox reaction of cerium oxides, as the basis of their use as catalysts, usually takes place at high temperature (>600 K) and/or low oxygen partial pressure. There have been continuous efforts to lower the operating temperatures of cerium oxide further to improve the performance of the catalysts and reduce pollution under the cold-start condition. Here, we report a direct atomic-scale observation of a redox process in cerium oxides driven by an electrical field at ambient temperature. The dynamic changes taking place during the electrically driven redox reaction were imaged by in situ high-resolution transmission electron microscopy, where reversible phase transformations due to the migration of oxygen vacancies have been reproducibly achieved. These results could lead to the low-temperature operation of catalysts for the purification of automobile emissions of pollutants, oxygen generation, and intermediate-temperature solid oxide fuel cells.

Effects of low concentration biodiesel blends application on modern passenger cars. Part 3: Impact on PAH, nitro-PAH, and oxy-PAH emissions

This study explores the impact of five different types of methyl esters on polycyclic aromatic hydrocarbon (PAH), nitrated-PAH and oxygenated PAH emissions. The measurements were conducted on a chassis dynamometer, according to the European regulation. Each of the five different biodiesels was blended with EN590 diesel at a proportion of 10-90% v/v (10% biodiesel concentration). The vehicle was a Euro 3 compliant common-rail diesel passenger car. Emission measurements were performed over the NEDC and compared with those of the real traffic-based Artemis driving cycles. The experimental results showed that the addition of biodiesel led to some important increases in low molecular-weight PAHs (phenanthrene and anthracene) and to both increases and reductions in large PAHs which are characterised by their carcinogenic and mutagenic properties. Nitro-PAHs were found to reduce with biodiesel whereas oxy-PAH emissions presented important increases with the biodiesel blends. The impact of biodiesel source material was particularly clear on the formation of PAH compounds. It was found that most PAH emissions decreased as the average load and speed of the driving cycle increased. Cold-start conditions negatively influenced the formation of most PAH compounds. A similar trend was observed with particulate alkane emissions.

Study of Ethanol Blending Effects on Formation of Mixture under Cold Start Conditions

Study of Ethanol Blending Effects on Formation of Mixture under Cold Start Conditions

Benefits and challenges of variable compression ratio at diesel engines

The compression ratio strongly affects the working process and provides an exceptional degree of control over engine performance. In conventional internal combustion engines, the compression ratio is fixed and their performance is therefore a compromise between conflicting requirements. One fundamental problem is that drive units in the vehicles must successfully operate at variable speeds and loads and in different ambient conditions. If a diesel engine has a fixed compression ratio, a minimal value must be chosen that can achieve a reliable self-ignition when starting the engine in cold start conditions. In diesel engines, variable compression ratio provides control of peak cylinder pressure, improves cold start ability and low load operation, enabling the multi-fuel capability, increase of fuel economy and reduction of emissions. This paper contains both theoretical and experimental investigation of the impact that automatic variable compression ratios has on working process parameters in experimental diesel engine. Alternative methods of implementing variable compression ratio are illustrated and critically examined.

Screening of different zeolites and silicoaluminophosphates for the retention of propene under cold start conditions

Propene adsorption isotherms, breakthrough curves and temperature programme desorption profiles have been obtained for six different crystalline materials with distinctive framework structures (3D and 1D) and a variety of Si/Al ratios and cations (four zeolites: Silicalite-1, BETA, ZSM-5, Mordenite; and two silicoaluminophosphate molecular sieves: SAPO-41 and SAPO-5). Moreover, for a proper evaluation of the solids in a propene trap under cold start conditions, cold start tests have been performed, carrying out four cycles (adsorption/desorption) to analyze the ageing process of the materials. A detailed analysis of the experimental results points out that materials with high equilibrium propene adsorption capacity at 30 °C, where propene is mainly chemisorbed and, which presents some kinetics restrictions, seem to be the best for a propene trap under cold start conditions. BETA and ZSM-5 zeolites and SAPO-5 silicoaluminophosphate molecular sieve are promising materials as propene traps.

Comparison of Exhaust Emissions Resulting from Cold- and Hot-Start Motorcycle Driving Modes

This study investigated the emissions of criteria air pollutants (carbon monoxide [CO], hydrocarbons [HCs], and oxides of nitrogen [NOx]) from motorcycle exhaust at cold- and hot-start driving cycles on a chassis dynamometer. Seven four-stroke carburetors and two fuel-injection motorcycles were tested. As expected, the emission factors (g/km) of CO and HCs increased during cold-start driving. The ratio of emission factors (g/km) for cold- and hot-start driving cycles ranged from 1.1–1.5 (for CO) to 1.2–2.8 (for HCs). However, the difference of NOx emissions between the cold- and hot-start cycles was not pronounced. Further, the cold-/hot-start ratios of CO and HCs from 50-cm3 motorcycles were higher than those of 100- and 125-cm3 motorcycles; however, the carbon dioxide (CO2) emission was the lowest for the four-stroke motorcycles. High engine temperature and poor combustion efficiency of smaller cylinder-capacity motorcycles may contribute a significant amount of exhaust emission. Additionally, the fuel-base emission factor (g/L-fuel) ratios were low compared with the distance-base emission factor (g/km) in cold- and hot-start driving. This indicates that the effect of catalyst efficiency was greater than the effect of fuel combustion in the tested motorcycles. A comparison of emission ratios of motorcycles and passenger cars shows that the warm-up may be more important for cars, especially under low-temperature conditions. However, the motorcycle contributes a large proportion of CO and HC emissions in many Asian counties. The difference between cold- and hot-start emissions may affect inventory accuracy, especially in HC emissions. For those tropical or subtropical countries in which motorcycles are one of the dominant air pollution sources, optimizing the engine combustion efficiency and developing new catalyst technology of motorcycles at cold-start conditions are the key issues to be improved.

Fundamental Research Needs in Combined Water and Thermal Management Within a Proton Exchange Membrane Fuel Cell Stack Under Normal and Cold-Start Conditions

Each fuel cell component of a proton exchange membrane fuel cell (PEMFC) used in automotive application operates most effectively (from performance and durability standpoints) within specific ranges of water content and temperature. The water and heat transport processes are coupled and present a challenge in providing the right balance over the entire range of operating conditions. Another important related aspect is CO poisoning of the electrocatalyst, which adversely affects the fuel cell performance. Freezing and cold-start present additional challenges for automotive PEMFCs. A critical review of the recent developments on these topics is presented in this paper. The study covers both the microscopic and macroscopic aspects of the transport within membrane, catalyst layers, gas diffusion layers, and gas channels, and an overview of the current PEMFC cooling technology. After discussing the current status, suggestions for future work on the above topics are presented.

Three dimensional water and ice quantification using neutron imaging

Neutron radiography (NR) and computed tomography (NCT) are important non-destructive testing tools which determine information about an object’s interior structure and material properties. Although water quantification using 2-D neutron imaging has been applied to fuel cells for over a decade, the development of an accurate 3-D method has only recently been demonstrated. The 3-D water quantification technique developed at the Pennsylvania State University’s Radiation Science and Engineering Center has been applied to the quantification of both liquid and ice phase water. Quantification results of water and ice inside a known small channel test object were accurate to within 2%. This capability allows the quantification of ice within a fuel cell flow field under cold-start conditions.

Applications of CFD Modeling in GDI Engine Piston Optimization

This paper describes a CFD modeling based approach to address design challenges in GDI (gasoline direct injection) engine combustion system development. A Ford in-house developed CFD code MESIM (Multidimensional Engine Simulation) was applied to the study. Gasoline fuel is multi-component in nature and behaves very differently from the single component fuel representation under various operating conditions. A multi-component fuel model has been developed and is incorporated in MESIM code. To apply the model in engine simulations, a multi-component fuel recipe that represents the vaporization characteristics of gasoline is also developed using a numerical model that simulates the ASTM D86 fuel distillation experimental procedure. The effect of the multi-component model on the fuel air mixture preparations under different engine conditions is investigated. The modeling approach is applied to guide the GDI engine piston designs. Effects of piston designs on the fuel air mixture preparation are presented. It is found that the multi-component fuel model is critical to the accuracy of the model prediction of the fuel air preparation process, particularly under cold start conditions.

Vortex ring-like structures in gasoline fuel sprays under cold-start conditions

A phenomenological study of vortex ring-like structures in gasoline fuel sprays is presented for two types of production fuel injectors: a low-pressure, port fuel injector (PFI) and a high-pressure atomizer that injects fuel directly into an engine combustion chamber (G-DI). High-speed photography and phase Doppler anemometry (PDA) were used to study the fuel sprays. In general, each spray was seen to comprise three distinct periods: an initial, unsteady phase; a quasi-steady injection phase; and an exponential trailing phase. For both injectors, vortex ring-like structures could be clearly traced in the tail of the sprays. The location of the region of maximal vorticity of the droplet and gas mixture was used to calculate the temporal evolution of the radial and axial components of the translational velocity of the vortex ring-like structures. The radial components of this velocity remained close to zero in both cases. The experimental results were used to evaluate the robustness of previously developed models of laminar and turbulent vortex rings. The normalized time, , and normalized axial velocity, , were introduced, where tinit is the time of initial observation of vortex ring-like structures. The time dependence of on was approximated as and for the PFI and G-DI sprays respectively. The G-DI spray compared favourably with the analytical vortex ring model, predicting , in the limit of long times, where α = 3/2 in the laminar case and α = 3/4 when the effects of turbulence are taken into account. The results for the PFI spray do not seem to be compatible with the predictions of the available theoretical models.

Cold Start on Low Compression Ratio Diesel Engine: Experimental and 3D RANS Computation Investigations

Diesel engines' future emission standards require greatly reducing the pollutant emissions directly at the exit of the engine before post-processing. The reduction of NOx “production” with very low levels of Particulate Matter (PM), HC and CO must be performed without damaging the drivability, and keeping fuel consumption and combustion noise under control. The reduction of the Compression Ratio (CR) is one of the most promising ways to achieve this challenge. The counterpart of reducing Diesel engine CR is the decrease in start ability. As a consequence, a stringent limitation of reducing Diesel CR is cold start requirements. Indeed, reduction of ambient temperature leads to penalties in fuel vaporization and auto-ignition capabilities, even more at very low temperature (–20°C and below). This paper presents the work performed on a HSDI Common-Rail Diesel 4-cylinder engine. Three kinds of investigations were used: experiments performed at very low temperature (down to –25°C); incylinder imaging (videoscope) and three-dimensional Computational Fluid Dynamics (CFD) computations in cold start conditions. The combustion chamber was adapted in order to reach a low compression ratio (CR 13.7:1) by modifying the piston bowl shape. First, experimental results obtained with a low CR engine are compared with those obtained with the original conventional CR engine. Then, a complete recalibration of injection settings (fuel quantity and timing, injection pressure, etc.) was carried out. It allows one to significantly reduce start delay with a low CR engine and the reference start delay with the conventional CR becomes reachable. In addition, effects of combustion chamber design such as spray position according to the glow plug were studied and show a great potential regarding behavior in cold conditions in particular, in order to reduce start delay again in such conditions. In order to complete the engine tests, CFD calculations were performed during the starting operation in ambient cold conditions (–20°C). The obtained results are in good agreement with optical observations and in-cylinder pressure measurements. Correlations between experiments and calculations give consistent explanations concerning the different phenomena occurring during cold start.