Heavy-duty Direct Injection Diesel Engine Research Articles

Effect of early intake valve closing, exhaust gas recirculation and split injection on combustion and emissions characteristics of a HDDI diesel engine operating in PCCI combustion mode

Premixed Charge Compression Ignition (PCCI) combustion is an alternative to conventional diffusion-controlled combustion for Mono-nitrogen oxides (NOx) and soot emissions reduction in DI diesel engines. However, bringing the center of combustion (CoC) near top dead center (TDC) to reduce brake specific fuel consumption is challenging. In this study, for two Early Intake Valve Closing (EIVC) profiles of split injection strategy, combustion characteristics and emissions of a heavy-duty direct injection (HDDI) diesel engine are evaluated by CFD simulations. Combustion efficiency, Indicated Specific Fuel Consumption (ISFC), NOx, soot, and carbon monoxide (CO) emissions are evaluated for 40 ˚CA and 80˚CA EIVC timings with respect to the base diesel combustion with 0, 30, 50, and 70% Exhaust Gas Recirculation (EGR) rates at 3 bar Brake Mean Effective Pressure (BMEP).CFD simulations reveal that EIVC strategy can displace the CoC towards TDC up to 5–10 ˚CA depending on the EGR rate. Moreover, up to 30% NOx reduction can be achieved in EIVC cases. In 70% EGR case, lower ISFC and near zero NOx emissions can be obtained compared to conventional diesel combustion due to CoC being closer to TDC. However, the EIVC strategy with EGR increases CO emissions due to incomplete combustion of a lower air/fuel ratio mixture.

Elevated emissions of volatile and nonvolatile nanoparticles from heavy-duty diesel engine running on diesel-gas co-fuels

This study experimentally examines the effects of four diesel-gas co-fuels, two engine loads and an aftertreatment on regulated and unregulated emissions from a 6-cylinder natural-aspirated direct-injection heavy-duty diesel engine (HDDE) with an engine dynamometer. Fuel energy of ultra-low-sulfur diesel was substituted with 10% and 20% of gas fuels, including pure H2, CH4, and two CH4-CO2 blends. The particle number size distributions of volatile and nonvolatile nanoparticles were measured under ambient temperature and after 300 °C heating, respectively. The results show that the gas fuels caused increases of hydrocarbon emission, slight changes of NOx emission, and decreases of opacity. All four gas fuels resulted in elevated emissions of both volatile and nonvolatile nanoparticles at 25% and 75% load, in the range of 29% to 390%. The increased emissions of volatile nanoparticles were variable and without obvious trends. Special attentions should be given to the addition of H2 under high load, during which significant increases of volatile nanoparticles could be formed not only post-combustion (up to 1376%), but also post-diesel oxidation catalyst plus diesel particulate filter (DOC + DPF). The nonvolatile nanoparticles, on the other hand, could be effectively removed by the retrofitted DOC + DPF, with efficiency >98.2%. A noteworthy fraction of solid particles of sizes <23 nm were found in the exhaust, not being accounted for by current regulatory emission standard.

Raman spectroscopy of diesel and gasoline engine-out soot using different laser power

We studied engine-out soot samples collected from a heavy-duty direct-injection diesel engine and port-fuel injection gasoline spark-ignition engine. The two types of soot samples were characterized using Raman spectroscopy with different laser powers. A Matlab program using least-square-method with trust-region-reflective algorithm was developed for curve fitting. A DOE (design of experiments) method was used to avoid local convergence. The method was used for two-band fitting and three-band fitting. The fitting results were used to determine the intensity ratio of D (for “Defect” or “Disorder”) and G (for “Graphite”) Raman bands. It is found that high laser power may cause oxidation of soot sample, which gives higher D/G intensity ratio. Diesel soot has consistently higher amorphous/graphitic carbon ratio, and thus higher oxidation reactivity, compared to gasoline soot, which is reflected by the higher D/G intensity ratio in Raman spectra measured under the same laser power.

Improvement of engine performance and emissions by biomass oil filter in diesel engine

In this study, a modified-sawdust lubricant oil filter (MSF) was developed and its effect on emission characteristic and performance of diesel engine was studied compared with conventional fiber-paper oil filter (CPF). The tests were performed using a six-cylinder, heavy-duty direct injection diesel engine. In steady state, the brake-specific fuel consumption (BSFC), engine output power and engine oil pressure were measured at nine different typical engine speeds. Exhaust emissions of nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO) and hydrocarbons (HC) were analyzed according to European Steady-state Cycle (ESC). Besides, lubricant oil samples were extracted from the crankcase in the equipment of MSF and CPF individually. Then the kinematic viscosity, colloids and metal content of oil samples were determined. The results showed that MSF effectively reduced wear metal accumulation and insoluble colloids in lubricating oil, and thus retarded deterioration of oil viscosity. Compared with CPF, an increase of 2.7 kW in maximum output power and decrease of 1.66–2.85% in BSFC were observed for MSF. In addition, the using of MSF significantly reduced HC (60.9%) and PM (12.5%) emission while increased CO and NOx emission slightly. The results proved that MSF is a suitable choice for diesel engine to improve engine performance and reduce exhaust emissions.

Impact of properties of vegetable oil, bio-diesel, ethanol and n -butanol on the combustion and emissions of turbocharged HDDI diesel engine operating under steady and transient conditions

The present work evaluates the impact of properties of four very common bio-fuels, viz. vegetable oil (cottonseed), or its derived (methyl ester) bio-diesel, or ethanol, or n-butanol, in blends of various proportions with diesel fuel, on the combustion and exhaust emissions of a fully instrumented, six-cylinder, four-stroke, heavy-duty direct injection (HDDI), ‘Mercedes-Benz’ bus diesel engine, bearing a waste-gate turbocharger with after-cooler, running under steady and transient conditions. Under steady-state operation, exhaust smoke, nitrogen oxides (NOx), carbon monoxide (CO), and total unburned hydrocarbons (HC) were measured and compared with those of the baseline operation (with neat diesel fuel) and among themselves. Fuel injection, combustion chamber pressure, and heat release rate (HRR) diagrams revealed interesting features of the combustion mechanisms. These results and the different physical and chemical properties of those bio-fuels are used to aid the interpretation of the observed engine behavior. As regards the transient engine operation, measurements for three accelerations tests were examined with the engine fueled on bio-diesel or n-butanol diesel fuel blends. The test bed was complemented with fast response instruments to capture the development of key engine and turbocharger variables, depicted in analytical diagrams, using ultra-fast response instrumentation for the instantaneous measurements of the exhaust NO and smoke opacity. Again, these results and the different physical and chemical properties of bio-fuels are used to aid the interpretation of the engine behavior. Finally, a comparison is made for the influence of bio-fuels properties (bio-diesel and n-butanol) on the NOx and smoke emissions between steady-state and transient operating conditions, under the recognition of the different non-fuel factors affecting the transient operating schedules.

Diesel-Ignited Propane Dual Fuel Low Temperature Combustion in a Heavy-Duty Diesel Engine

This paper presents an experimental analysis of diesel-ignited propane dual fuel low temperature combustion (LTC) based on performance, emissions, and in-cylinder combustion data from a modern, heavy-duty diesel engine. The engine used for these experiments was a 12.9-liter, six-cylinder, direct injection heavy-duty diesel engine with electronic unit diesel injection pumps, a variable geometry turbocharger, and cooled exhaust gas recirculation (EGR). The experiments were performed with gaseous propane (the primary fuel) fumigated upstream of the turbocharger and diesel (the pilot fuel) injected directly into the cylinders. Results are presented for a range of diesel injection timings (SOIs) from 10 deg BTDC to 50 deg BTDC at a brake mean effective pressure (BMEP) of 5 bar and a constant engine speed of 1500 rpm. The effects of SOI, percent energy substitution (PES) of propane (i.e., replacement of diesel fuel energy with propane), intake boost pressure, and cooled EGR on the dual fuel LTC process were investigated. The approach was to determine the effects of SOI while maximizing the PES of propane. Dual fuel LTC was achieved with very early SOIs (e.g., 50 deg BTDC) coupled with high propane PES (&gt;84%), which yielded near-zero NOx (&lt;0.02 g/kW h) and very low smoke emissions (&lt;0.1 FSN). Increasing the propane PES beyond 84% at the SOI of 50 deg BTDC yielded a high COV of IMEP due to retarded combustion phasing (CA50). Intake boost pressures were increased and EGR rates were decreased to minimize the COV, allowing higher propane PES (∼93%); however, lower fuel conversion efficiencies (FCE) and higher HC and CO emissions were observed.

Combustion and emissions characteristics of fish oil fuel in a heavy-duty diesel engine

Residual fish oil, which is basically a by-product of fish processing industry, was tested pure and in 50% v/v blend with conventional low-sulfur marine gas oil in a direct-injection heavy-duty diesel engine. Experiments were performed at various operating conditions under standard propulsion and generator mode marine cycles. Engine performance, exhaust smokiness, gaseous emissions together with particulate matter (PM) size distribution and corresponding total particle number and mass concentrations were measured in all of the tests performed. In general, fish oil showed fairly good combustion and ignition properties, which were very similar to that of marine gas oil. Only slight difference was observed in NOx and CO2 levels, while emissions of CO and THC were significantly decreased at all operating conditions. Fish oil also allows reducing smoke (soot) and both total number and PM mass emissions up to 70–90% with the biggest particles being most affected. Such positive impact on pollutants can be explained by high oxygen content in fish oil fuel and its lack of aromatic compounds, which is promoting more complete fuel oxidation.

Evolution of the nanostructure, fractal dimension and size of in-cylinder soot during diesel combustion process

The nanostructure, fractal dimension and size of in-cylinder soot during diesel combustion process have been investigated for a heavy-duty direct injection diesel engine, using a total cylinder sampling system followed by high-resolution transmission electron microscopy and Raman scattering spectrometry. Different structural organizations of in-cylinder soot are found depending upon the combustion phase. It is revealed that both the fringe tortuosity and separation distance decrease as combustion proceeds, while the mean fringe length increases distinctly from 1.00 to 2.13 nm, indicating the soot evolution toward a more graphitic structure during the combustion process. The fractal dimensions of aggregates are in a range of 1.20–1.74 at various crank angles under the applied engine operating conditions. As temperature and pressure increase, the fractal dimension decreases significantly to a minimum at the early diffusion combustion stage. The soot particles become more compact again as the fractal dimension increases during the subsequent combustion period. Primary particle sizes start small, go through a maximum in the early diffusion combustion phase and decline again as combustion proceeds.

Combustion heat release analysis of ethanol or n-butanol diesel fuel blends in heavy-duty DI diesel engine

An experimental study is conducted to evaluate the effects of using blends of diesel fuel with either ethanol in proportions of 5% and 10% or n-butanol in 8% and 16% (by vol.), on the combustion behavior of a fully-instrumented, six-cylinder, turbocharged and after-cooled, heavy duty, direct injection (DI), ‘Mercedes-Benz’ engine installed at the authors’ laboratory. Combustion chamber and fuel injection pressure diagrams are obtained at two speeds and three loads using a developed, high-speed, data acquisition and processing system. A heat release analysis of the experimentally obtained cylinder pressure diagrams is developed and used. Plots of histories in the combustion chamber of the heat release rate and temperatures reveal some interesting features, which shed light into the combustion mechanism when using these promising bio-fuels that can be derived from biomass (bio-ethanol and bio-butanol). The key results are that with the use of these bio-fuels blends, fuel injection pressure diagrams are very slightly displaced (delayed), ignition delay is increased, maximum cylinder pressures are slightly reduced and cylinder temperatures are reduced during the first part of combustion. These results, combined with the differing physical and chemical properties of the ethanol and n-butanol against those for the diesel fuel, which constitutes the baseline fuel, aid the correct interpretation of the observed engine behavior performance- and emissions-wise.

Relation between hydroxyl and formaldehyde in a direct-injection heavy-duty diesel engine

Formaldehyde and the hydroxyl radical have been recorded simultaneously in a diesel spray in an optically-accessible heavy-duty diesel engine. Formaldehyde (CH 2O) was excited by 355 nm radiation, while hydroxyl (OH) was excited around 284 nm. Both laser beams were focussed into a sheet, of which the overlap while traversing the spray was monitored. The experimental results have been compared to simulations. The ignition phase was modeled by a set of homogeneous reactors, while the diffusion combustion phase was simulated by a flamelet approach, viz. a rich partially premixed counterflow diffusion flame. Two situations were tested, one in which the combustion started only after the end of injection (short and early injection) and one with a longer injection duration where injection and combustion partly overlapped in time. In the former, OH initially shows up far from the injector and then quickly proceeds towards the injector. The position of OH varied significantly from cycle to cycle, suggesting that the combustion is partly governed by turbulence. When combustion and injection do partly overlap, the flame structure is much more stable. In both cases, OH and CH 2O generally form complementing spatial distributions, indicating that CH 2O is consumed locally during the hot combustion.

Carbonyl compound emissions from a heavy-duty diesel engine fueled with diesel fuel and ethanol–diesel blend

This paper presents an investigation of the carbonyl emissions from a direct injection heavy-duty diesel engine fueled with pure diesel fuel (DF) and blended fuel containing 15% by volume of ethanol (E/DF). The tests have been conducted under steady-state operating conditions at 1200, 1800, 2600 rpm and idle speed. The experimental results show that acetaldehyde is the most predominant carbonyl, followed by formaldehyde, acrolein, acetone, propionaldehyde and crotonaldehyde, produced from both fuels. The emission factors of total carbonyls vary in the range 13.8–295.9 mg (kW h) −1 for DF and 17.8–380.2 mg (kW h) −1 for E/DF, respectively. The introduction of ethanol into diesel fuel results in a decrease in acrolein emissions, while the other carbonyls show general increases: at low engine speed (1200 rpm), 0–55% for formaldehyde, 4–44% for acetaldehyde, 38–224% for acetone, and 5–52% for crotonaldehyde; at medium engine speed (1800 rpm), 106–413% for formaldehyde, 4–143% for acetaldehyde, 74–113% for acetone, 114–1216% for propionaldehyde, and 15–163% for crotonaldehyde; at high engine speed (2600 rpm), 36–431% for formaldehyde, 18–61% for acetaldehyde, 22–241% for acetone, and 6–61% for propionaldehyde. A gradual reduction in the brake specific emissions of each carbonyl compound from both fuels is observed with increase in engine load. Among three levels of engine speed employed, both DF and E/DF emit most CBC emissions at high engine speed. On the whole, the presence of ethanol in diesel fuel leads to an increase in aldehyde emissions.

Effects of High Injection Pressure, EGR and Charge Air Pressure on Combustion and Emissions in an HD Single Cylinder Diesel Engine

When increasing EGR from low levels to a level that corresponds to low-temperature combustion, soot emissions initially increase due to lower soot oxidation before decreasing to almost zero due to very low soot formation. At the EGR level where soot emissions start to increase, the NOx emissions are low, but not sufficiently low to comply with future emission standards and at the EGR level where low-temperature combustion occurs CO and HC emissions are too high. The purpose of this study was to investigate the possibilities for shifting the so-called soot bump (where soot levels are increased) to higher EGR levels, or to reduce the magnitude of the soot bump using very high injection pressures (up to 240 MPa) while reducing the NOx emissions using EGR. The possibility of reducing the CO and HC emissions at high EGR levels due to the increased mixing caused by higher injection pressure was also investigated and the flame was visualized using an endoscope at chosen EGR values. In addition, flame temperatures and soot volume fractions were determined using two-color pyrometry. A single-cylinder heavy-duty direct injection diesel engine equipped with an electronically controlled unit injector with variable needle opening pressure was used in the investigations, with geometry based on the Volvo D12C production engine but with the compression ratio reduced from 18.5 to 14. The results from the studied cases showed that increasing EGR from 0 to 30% reduces both soot formation and oxidation resulting in higher engine-out soot emissions. Also, an increase in NOP for a case without EGR was found to give both high soot formation and high soot oxidation, resulting in reduced engine-out soot emissions. When EGR was added, increased NOP resulted in increased soot oxidation and thus in lower engine-out soot emissions. An increase in NOP was also found to reduce HC and CO emissions at high EGR levels.

Effects of ethanol–diesel fuel blends on the performance and exhaust emissions of heavy duty DI diesel engine

An experimental investigation is conducted to evaluate the effects of using blends of ethanol with conventional diesel fuel, with 5% and 10% (by vol.) ethanol, on the performance and exhaust emissions of a fully instrumented, six-cylinder, turbocharged and after-cooled, heavy duty, direct injection (DI), Mercedes–Benz engine, installed at the authors’ laboratory, which is used to power the mini-bus diesel engines of the Athens Urban Transport Organization sub-fleet with a view to using bio-ethanol produced from Greek feedstock. The tests are conducted using each of the above fuel blends, with the engine working at two speeds and three loads. Fuel consumption, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides, carbon monoxide and total unburned hydrocarbons are measured. The differences in the measured performance and exhaust emissions of the two ethanol–diesel fuel blends from the baseline operation of the engine, i.e. when working with neat diesel fuel, are determined and compared. Theoretical aspects of diesel engine combustion combined with the widely differing physical and chemical properties of the ethanol against those for the diesel fuel, are used to aid the correct interpretation of the observed engine behavior.

Diesel Engine Simulations with Multi-Dimensional Conditional Moment Closure

First-order elliptic Conditional Moment Closure (CMC), coupled with a computational fluid dynamics (CFD) solver, has been employed to simulate combustion in a direct-injection heavy-duty diesel engine. The three-dimensional structured finite difference CMC grid has been interfaced to an unstructured finite volume CFD mesh typical of engine modelling. The implementation of a moving CMC grid to reflect the changes in the domain due to the compression and expansion phases has been achieved using an algorithm for the cell addition/removal and modelling the additional convection term due to the CMC cell movement. Special care has been taken for the boundary conditions and the wall heat transfer. An operator splitting formulation has been used to integrate the CMC equations efficiently. A CMC domain reduction of the three-dimensional problem to two- and zero-dimensions through appropriate volume integration of the CMC equation has been explored in terms of accuracy and computational time. Additional considerations have been reported concerning the initialization of the CMC domain in conserved scalar space during transient calculations where the probability density function of the mixture fraction changes drastically with time as during fuel injection. Predictions compare favourably with the experimental pressure traces for tests at full and half load. A balance of terms in the CMC equation allows conjectures on the structure of the flame and its expansion across the spray after autoignition.

In-cylinder unburned hydrocarbon visualization during low-temperature compression-ignition engine combustion using formaldehyde PLIF

Formaldehyde (H 2CO) is visualized by planar laser-induced fluorescence (PLIF) in a heavy-duty direct-injection diesel engine to better understand the sources of unburned hydrocarbon (UHC) emissions. H 2CO is used as a tracer for UHC based on chemical kinetic simulations, which show that after the first-stage of ignition, the evolution of H 2CO is very similar to that of UHC in the bulk gases. Modern low-temperature, low-nitrogen oxides (NO x ) combustion conditions are achieved by diluting the intake stream with nitrogen to 12.7% oxygen by volume, simulating exhaust gas recirculation. A range of ignition delays (IDs) is produced by adjusting the intake temperature and/or the fuel injection timing. Spectral measurements of the laser-induced emission after 355-nm excitation show that broadband emission from sources other than H 2CO can be significant, so the PLIF images must be interpreted with care. A frequency-domain covariance analysis is offered as a way to quantify the contribution of H 2CO fluorescence in the images. Longer ID conditions are found to have both higher-UHC emissions and stronger H 2CO fluorescence persisting late in the cycle, especially near the injector. Based on kinetic model predictions of longer H 2CO lifetimes in leaner regions, it is concluded that for long ID conditions, mixtures near the injector after the end of injection are too lean to achieve complete combustion, thus contributing to UHC emissions.

Controlling D.I. Diesel Engine Emissions Using Multiple Injections and EGR

Experiments have been performed using a modern heavy-duty direct-injection diesel engine equipped with a common-rail, electronically-controlled high-pressure fuel injection system. The experimental results demonstrate the utility of using multiple or split fuel injections in combination with EGR for giving significant emissions reduction over the entire engine operating range. The mechanisms of emission reduction have been revealed by means of combustion visualization and CFD modeling. Soot is reduced due to the fact that the soot producing regions at the tip of the sprays are not replenished with fresh fuel when each injection is terminated and then restarted. The large reduction in soot possible with multiple injections allows the use of higher levels of EGR than is possible with single injections, so that NOx can be reduced significantly while soot levels are simultaneously kept low.