Start Of Injection Timing Research Articles

Effect of two-stage injection dwell angle on engine combustion and performance characteristics of a common-rail diesel engine fueled with coconut oil methyl esters-diesel fuel blends

Diesel engine is widely used as prime mover due to its high thermal efficiency. Usage of renewable biodiesel in diesel engine is also widely studied due to its potential in reducing emission and as a replacement of conventional diesel. Biodiesel performance could be improved by blending it with petroleum diesel besides introducing appropriate injection strategies. In this experiment, the effect of percentage of biodiesel blends and injection strategies such as variations in start of injection (SOI) timing and dwell angle on diesel engine performance were investigated. The test engine used is four-stroke turbocharged direct injection diesel engine. Results show that exhaust emissions, engine performance and combustion characteristics are substantially affected by biodiesel blending ratio and SOI timing but slightly influenced by two-stage injection dwell angle. Biodiesel blends percentage could be raised to improve NOx and smoke emissions. Even though SOI performed at a later timing could reduce NOx emission, smoke emission increased. Dwell angle between two successive injections could be prolonged to lower the effect of the increase in smoke emission. It could also be inferred that by setting a proper SOI timing and dwell angle under two-stage injection scheme when suitable biodiesel blend is used, the engine performance could be optimized.

Development of combustion strategy for the internal combustion engine fueled by ammonia and its operating characteristics

Focusing on the possibility of using ammonia as a hydrogen carrier, a combustion strategy for pure ammonia as an engine fuel to convert the stored energy into a usable form has been proposed, which uses ammonia itself as a combustion promotor. Under this strategy, the conditions of sufficiently high temperature and pressure to cause the spray combustion of ammonia are obtained by the auto-ignition of a mixture of pilot-injected ammonia and air. To confirm the feasibility and the operating characteristics of an engine with the proposed ammonia combustion strategy, engine modeling has been conducted, the combustion strategy has been simulated, and a parametric study has been performed. To analyze the NO production mechanisms in an engine with the proposed combustion strategy, the NO production process has been classified into four phases, and the NO production in each phase has been analyzed under various start of injection timing and fuel amounts.

Trade-off on fuel economy, knock, and combustion stability for a stratified flame-ignited gasoline engine

A combination of port fuel injection (PFI) and direct injection (DI), called P-DI strategy, was used in a four-cylinder gasoline engine. The aim was to achieve a stratified flame ignition (SFI) hybrid combustion and manage the trade-off among fuel economy, knock, and combustion stability (EKS) in a gasoline engine. In the proposed P-DI strategy, DI was used to enrich the local mixture around the spark plug to enhance the early spark-ignition combustion. On the other hand, PFI was used to form a largely lean homogeneous mixture to achieve a moderately controlled auto-ignition combustion in the outer region of the cylinder. The effects of DI fraction (RDI) and start of injection (SOI) timing of DI on the SFI hybrid combustion were investigated experimentally. It was found that an increased RDI resulted in a parabolic-like effect on the combustion phasing and combustion stability. The earliest combustion phasing was achieved with an RDI of approximately 35%. The fuel economy deteriorated monotonously with increasing RDI. In comparison, the effect of SOI on the SFI hybrid combustion was more complicated. It was found that an SOI between 50°CA before top-dead-center (BTDC) and 90°CA BTDC showed a potential to achieve a satisfactory trade-off among EKS. Based on the above findings, a cost function (J) was proposed to represent the EKS trade-off and reduce the calibration burden for optimal SOI at different engine operating conditions. An extremum-seeking algorithm was adopted to search for the maximum value of J and obtain the optimal SOI timing at each operating point. The proposed algorithm was then validated by experimental results.

Numerical Study of Natural Gas/Diesel Reactivity Controlled Compression Ignition Combustion with Large Eddy Simulation and Reynolds-Averaged Navier–Stokes Model

In the current study, a comparative study is performed using Large Eddy Simulation (LES) and Reynolds-averaged Navier–Stokes (RANS) turbulence models on a natural gas/diesel Reactivity Controlled Compression Ignition (RCCI) engine. The numerical results are validated against the available research work in the literature. The RNG (Re-Normalization Group) k − ε and dynamic structure models are employed to model turbulent flow for RANS and LES simulations, respectively. Parameters like the premixed natural gas mass fraction, the second start of injection timing (SOI2) of diesel and the engine speed are studied to compare performance of RANS and LES models on combustion and pollutant emissions prediction. The results obtained showed that the LES and RANS model give almost similar predictions of cylinder pressure and heat release rate at lower natural gas mass fractions and late SOI2 timings. However, the LES showed improved capability to predict the natural gas auto-ignition and pollutant emissions prediction compared to RANS model especially at higher natural gas mass fractions.

Investigation on performance and emission characteristics of EGR coupled semi adiabatic diesel engine fuelled by DEE blended rubber seed biodiesel

The test case was semi adiabatic diesel engine (SADE) produced by thermal barrier 8 YSZ (Yttria Stabilized Zirconia) ceramic coated cylinder head and liner with bond coat NiCrAl as an intermediate layer and coupled with an EGR (exhaust gas recirculation) of 10% constant rate. The test fuels injected directly into the combustion chamber are diesel and blend A15B85 by vol. (Additive Diethyl Ether 15% + Rubber seed based Biodiesel 85%). Throughout the experimentation, a constant compression ratio 18:1, fuel injection pressure 190 bar and speed 1800 rpm. Load from 0% to 100% and start of injection (SOI) timing from 300 BTDC to 350 BTDC were varied to investigate performance, in-cylinder pressure and emission parameters of SADE and ordinary diesel engine (ODE) fuelled by test fuels. It was found that advancement of SOI timing improved all the investigated parameters except NOx emissions. Compared to ODE with diesel at any specific SOI timing, the test case with blend found to be favourable. The optimum results of SADE were 7% enhancement of BTE with the reduction in BSEC by 5.5%, particulates by 48.5%, NOx by 19.5% and exhaust gas temperature by 18.5% found with the blend at 330 BTDC with higher load compared to ODE with neat diesel at 300 BTDC. The optimum configuration of ODE found to be diesel fuel at 340 BTDC with higher load.

Extending Substitution Limits of a Diesel–Natural Gas Dual Fuel Engine

New drilling techniques have increased availability and decreased costs of oil and gas. The decreased costs have caused an increase in drilling activity. The well sites have a large power demand that is typically met by diesel engines for the drilling derrick, fracking pumps, and electrical power. Dual fuel retrofit kits are being increasingly used at well sites to reduce operating costs and the amount of fuel trucked in to the site. Natural gas (NG) is cheaper compared to diesel and can be delivered to the site by the pipeline limiting the disturbance to surrounding communities due to diesel truck loads. The purpose of this work is to examine the performance of a typical dual fuel retrofit kit commissioned for field operation on a 6.8 L tier II diesel engine. After the baseline commissioning, the mechanisms limiting further substitution were clearly identified as engine knock similar to end gas auto-ignition in spark-ignited engines and governor instability. Two methods are examined for their ability to increase substitution limits by adjusting the start of injection timing (SOI) and the intake air manifold temperature. Retarding the SOI is able to delay the onset of knock at high loads and therefore increase the substitution level by around 4% at full load. At high loads, lowering the air manifold temperature is able to increase the substitution levels by around 10%. Preheating the intake air was able to increase low load substitution levels by 10% as well.

Numerical study on double injection techniques in a gasoline and biodiesel fueled RCCI (reactivity controlled compression ignition) engine

In an RCCI (reactivity controlled compression ignition) engine, the double injection strategy is a technical tool to control its combustion process. In this study, the effects of two key injection parameters, namely dwell and split fraction, are numerically investigated in a gasoline and biodiesel fueled RCCI engine. In the engine, gasoline is used as the premixed fuel; meanwhile, biodiesel is directly injected into the air-fuel mixture. The coupled KIVA4-CHEMKIN code was used to simulate the in-cylinder combustion process and the emissions formation. The gasoline/biodiesel reaction mechanism, which consists of 107 species and 425 reactions, was implemented in the code for detailed chemistry calculation. During the simulation, the dwells between 1st and 2nd SOI (start of injection) timings were varied at 5, 15, 25 and 35°CA, while the 1st SOI timing was fixed at −35 °C ATDC. Besides, the 1st pulse fractions were changed at 30%, 50% and 70%; accordingly, the rest of the biodiesel was injected through the 2nd pulse. The combustion characteristics (including in-cylinder pressure, HRR (heat release rate), ignition delay, PPRR (peak pressure rise rate) and combustion duration), engine performance and emissions (NO and soot) formations were compared under various operating conditions. The results show that double injection strategy results in longer ignition delay. In contrast with the dwells of 15° and 25°CA, the cases with dwells of 5° and 35°CA could result in acceptable PPRR, longer combustion duration, but slightly lower IMEP (indicated mean effective pressure). However, short dwell of 5°CA displays better results on NO and soot emissions. The combustion process with long dwell of 35°CA is both reactivity and mixing controlled.

Influence of injection timing and split injection strategies on performance, emissions, and combustion characteristics of diesel engine fueled with biodiesel blended fuels

Biodiesel can be used as alternative to replace fossil diesel. However, usage of biodiesel in an unmodified diesel engine can cause higher in nitrogen oxides (NOx) emission. In order to reduce the harmful emission, certain injection strategies can be carried out. In this paper, the effects of biodiesel blends, fuel injection timing and split injection schemes on the engine performance, emissions and combustion characteristics of a medium-duty diesel engine are investigated. Parametric studies relating with start of injection timing variation and multiple injection schemes using B20 and B50 biodiesel blends were performed and benchmarked with petroleum diesel fuel as baseline. A remarkably lower NOx level below 100 ppm can be obtained by retard start of injection (SOI) timing for both of the B20 and B50 fuel operations and with triple injection scheme. It was found that with the use of B50, simultaneous NOx and smoke suppression from the levels of petroleum diesel fuel is attainable in parallel with the implementation of late SOI timing and triple injection scheme in a diesel engine. In conclusion, multiple split injections is a practical strategies to simultaneously decrease NOx and smoke emissions when the SOI timing is fine-tuned and is an ideal alternative to operate with biodiesel fuel.

Analysis of mixture formation process in a two-stroke boosted uniflow scavenged direct injection gasoline engine

The two-stroke engine has the great potential for aggressive engine downsizing and downspeeding because of its double firing frequency. For a given torque, it is characterized with a lower mean effective pressure and lower peak in-cylinder pressure than a four-stroke counterpart. In order to explore the potential of two-stroke cycle while avoiding the drawbacks of conventional ported two-stroke engines, a novel two-stroke boosted uniflow scavenged direct injection gasoline engine was proposed and designed. In order to achieve the stable lean-burn combustion in the boosted uniflow scavenged direct injection gasoline engine, the mixture preparation, especially the fuel stratification around the spark plug, should be accurately controlled. As the angled intake scavenge ports produce strong swirl flow motion and complex transfer between the swirl and tumble flows in the two-stroke boosted uniflow scavenged direct injection gasoline engine, the interaction between the in-cylinder flow motions and the direct injection and its impact on the charge preparation in the boosted uniflow scavenged direct injection gasoline engine are investigated in this study by three-dimensional computational fluid dynamics simulations. Both the single injection and split injections are applied and their impact on the mixture formation process is investigated. The start of injection timing and split injection ratio are adjusted accordingly to optimize the charge preparation for each injection strategy. The results show that the strong interaction between the fuel injection and in-cylinder flow motions dominates the mixture preparation in the boosted uniflow scavenged direct injection gasoline engine. Compared to the single injection, the split injection shows less impact on the large-scale flow motions. Good fuel stratification around the spark plug was obtained by the late start of injection timings at 300 °CA/320 °CA with an equal amount in each injection. However, when a higher tumble flow motion is produced by the eight scavenge ports’ design, a better fuel charge stratification can be achieved with the later single injection at start of injection of 320 °CA.

Visualization of combustion performance and emission characteristics of a four-cylinder diesel engine at various injection timings and engine loads

In this study, the effects of injection timings on engine combustion, performance, and emission characteristics were investigated experimentally using a four-cylinder diesel engine equipped with an endoscopic visualization system. The experiments were conducted at constant speed (1500 rpm) with different start of injection timings and two loads (10 and 25% load, respectively). Premixed combustion was found from the heat release rate and combustion images with advanced injection. Additionally, larger area of luminous flames was obtained for retarded injection timing and higher engine load. It was also found that the area of soot distribution and flame temperature distribution decreased for advanced injection timing. NO x emission increased for advanced injection, however, an opposite trend was observed for lower load.

Performance optimization of diesel engine fueled with diesel–jatropha curcas biodiesel blend using response surface methodology

The present work is aimed at unfolding the effect of fuel supply parameters such as Fuel injection pressure (FIP), Start of injection timing (SOI), Pilot-main injection intervals (PMII) on performance and emission characteristics of 20 % blend of Jatropha curcas biodiesel (J20) under light load operation of a diesel engine. The experiments were designed using design of experiments based on the fractional factorial design of Response surface methodology (RSM). Multiple regression models developed using RSM for measured responses like nitrogen oxides (NOX), SOOT, hydrocarbon (HC), Brake specific fuel consumption (BSFC) and Brake thermal efficiency (BTE), were found to be statistically significant by Analysis of variance (ANOVA). Interactive effects among FIP, SOI and PMII were analyzed using response surface graphs that were fitted using developed RSM models. Optimization was performed using the desirability approach of the RSM for lesser emissions and BSFC simultaneously with superior BTE. A FIP of 134.11 MPa, SOI of 6.4 BTDC, and PMII of 5.8 CA were found to be optimal values for J20 in the test engine of 21 kW at 1800 rpm. The results of this study show that at optimal input parameters, the values of the NOX, SOOT, HC, BSFC and BTE with a high desirability of 96.7 % are 603.44 ppm, 0.037 FSN, 12.73 ppm, 233.26 g/kW h and 37.31 %, respectively.

A parametric study on engine performance and emissions with neat diesel and diesel-butanol blends in the 13-Mode European Stationary Cycle

This paper presents a comprehensive study of a wide range of engine performance parameters, including: indicated torque (IT), indicated power (IP), indicated mean effective pressure (IMEP) and indicated specific fuel consumption (ISFC). Further, the combustion parameters measured include: start of injection timing, in-cylinder peak pressure, boost pressure and rate of maximum pressure rise. Resultant emission parameters investigated include: exhaust blow by, unburned hydrocarbon (UBHC), oxides of nitrogen (NOx), particulate matter (PM), particle number (PN) and particle size distribution (PSD). Normal butanol (n-butanol) was chosen to blend with a reference diesel fuel. The experiment was conducted using a 6-cylinder, turbocharged common rail diesel engine in accordance with the 13-Mode European Stationary Cycle (ESC). Considering limits of solubility of n-butanol in reference diesel, a maximum of 30% n-butanol was blended with 70% reference diesel. Three different butanol blends having 10% butanol with 90% reference diesel, 20% butanol with 80% reference diesel and 30% butanol with 70% reference diesel (the blending percentages were on a volume basis) were prepared. The engine experimental results show that without considerably deteriorating engine performance, most of the emissions were significantly reduced with the butanol blends compared to those of the reference diesel.

Effect of diesel injection strategies on natural gas/diesel RCCI combustion characteristics in a light duty diesel engine

Reactivity controlled compression ignition (RCCI) combustion mode is an attractive combustion strategy due to its potential in satisfying the strict emission standards. In this study, the effects of direct injection (DI) strategies on the combustion and emission characteristics of a modified light duty RCCI engine, fueled with natural gas (NG) and diesel were numerically investigated. In this way, Converge CFD code employing a detail chemical kinetics mechanism was used for 3D simulation of combustion process and emissions prediction. NG with higher octane number (ON) is mixed with air through intake port, while diesel fuel with lower ON is directly injected into the combustion chamber during compression stroke by means of split injection strategy. The effects of several parameters, including the premixed ratio (PR) of NG, diesel fuel fraction in first and second injection pulses, first and second start of injection timing (SOI1 and 2), injection pressure and the spray angle on the engine performance and emission characteristics are investigated. The results indicate that these parameters have significant effects on the light duty RCCI engine performance and engine out emissions. Also, it was demonstrated that by decreasing the first injection pressure from 450 to 300bar, the gross indicated efficiency increases by 5% and CA50 is retarded by 4 CAD. Moreover, by reducing the spray angle from 144° to 100°, the gross indicated efficiency decreases by 4% and CA50 is advanced by 6 CAD. The results showed that reduction in NOx emission is achievable, while controlling HC and CO emissions, by means of increasing the NG fraction, advancing the SOI1, increasing the fuel fraction in first DI injection with lower injection pressure and employing a wider injector spray angle.

Particulate Matter Emission Suppression Strategies in a Turbocharged Gasoline Direct-Injection Engine

The development process of a down-sized turbocharged gasoline direct-injection (GDI) engine/vehicle was partially introduced with the focus on particulate matter (PM)/particle number (PN) emission reduction. To achieve this goal, the injection system was upgraded to obtain higher injection pressure. Two types of prototype injectors were designed and compared under critical test conditions. Combined numerical and experimental analysis was made to select the right injector in terms of particle emission. With the selected injector, the effect of injection parameters calibration (injection pressure, start of injection (SOI) timing, number of injection pulses, etc.) on PM/PN emission was illustrated. The number of fuel injection pulses, SOI timing, and injection pressure were found playing the leading role in terms of the particle emission suppression. With single-injection strategy, the injection pressure and SOI timing were found to be a dominant factor to reduce particle emission in warm-up condition and cold condition, respectively; a fine combination of injection timing and injection pressure is generally able to decrease up to 50% of PM emission in a wide range of the engine map. While with multiple injection, up to an order of magnitude PM emission reduction can be achieved. Several New European Driving Cycle (NEDC) emission cycles were arranged on a demo vehicle to evaluate the effect of the injection system upgrade and adjusted calibration. This work will provide a guide for the emission control of GDI engines/vehicles fulfilling future emission legislation.

Transition from HCCI to PPC: Investigation of Fuel Distribution by Planar Laser Induced Fluorescence (PLIF)

In a previous study, in order to investigate the effect of charge stratification on combustion behavior such as combustion efficiency and combustion phasing which also largely affects the emissions, an experiment was conducted in a heavy-duty compression ignition (CI) metal engine. The engine behavior and emission characteristics were studied in the transition from HCCI mode to PPC mode by varying the start of injection (SOI) timing. To gain more detailed information of the mixing process, in-cylinder laser diagnostic measurements, namely fuel-tracer planar laser induced fluorescence (PLIF) imaging, were conducted in an optical version of the heavy-duty CI engine mentioned above. To the authors’ best knowledge, this is the first time to perform fuel-tracer PLIF measurements in an optical engine with a close to production bowl in piston combustion chamber, under transition conditions from HCCI to PPC mode. Results show that four mixing schemes can be distinguished as the SOI timings are varied during the transition. They are linked to the results presented in the reference paper, where emissions were varied in different zones. For SOI at -100 crank angle degree (CAD), fuel distribution is homogeneous as expected. With other SOI timings, a significant part of the fuel mixture was trapped in the squish region and crevice area before start of combustion (SOC) as shown by PLIF results. The observations in the reference metal engine paper were confirmed by this measurement. Results are also in good agreement with computational fluid dynamics (CFD) simulations performed for this engine. (Less)

Combustion and exhaust emissions of canola biodiesel blends in a single cylinder DI diesel engine

In this study, effects of the canola biodiesel blends in 5%, 10%, 15% and 20% proportions (in vol.) with diesel fuel were investigated at four loads (4.8, 3.6, 2.4 and 1.2 bar BMEP) in a single-cylinder DI engine. Comprehensive combustion analyses showed that, although the start of injection timings were inadvertently advanced from the system response, the combustion of canola biodiesel blends generally resulted in shorter ignition delay period for all loads due to earlier combustion timing. The maximum heat release rate generally decreased gradually with the reduction of premixed combustion fractions and corresponding increase in the diffusion combustion fractions when the canola biodiesel ratio was increased. Slightly reducing the maximum in-cylinder pressures and maximum in-cylinder pressure rise rates were caused a slight retardation on the center of heat release locations and longer combustion durations. BSFC results increased up to 6.56% and BTE reduced up to 4.2% when the canola biodiesel ratio was increased to 20% at the high load. The canola biodiesel blends also resulted in higher NOx emissions of 8.9% as well as lower smoke, CO and THC but slightly higher CO2 emissions for all loads.

Multi-objective optimization of the combustion of a heavy-duty diesel engine with low temperature combustion under a wide load range: (I) Computational method and optimization results

By coupling a multi-dimensional computational fluid dynamics (CFD) code with genetic algorithm (GA), the combustion of a heavy-duty diesel engine with LTC (low temperature combustion) was optimized under a wide load range. At each load, a comprehensive optimization of the operating parameters including IVC (intake valve closing) timing, SOI (start of injection) timing, EGR (exhaust gas recirculation) rate, the initial in-cylinder pressure and temperature at IVC was conducted in order to simultaneously minimize ISFC (indicated specific fuel consumption), NOx (nitrogen oxides) and soot emissions, and seek the optimal control strategies. Furthermore, by employing the one-dimensional simulation, the correlation between the initial in-cylinder conditions at IVC and the intake conditions was developed. The optimization results indicate that the range of the operating parameters narrows considerably with increasing load. At low load, both early and late IVC timing can be employed. As late IVC is introduced, high intake pressure and high EGR rate up to 70% are needed to realize low NOx emissions, whereas low intake pressure and moderate EGR rate (around 40%) are necessary for early IVC. For both late and early IVC, the optimal SOI timing is 10–20 °CA BTDC (before top dead center) at low load to simultaneously avoid serious spray/wall impingement and diffusion combustion. At mid load, IVC timing should be advanced to 104–110 °CA BTDC with a moderate EGR rate (40%–50%) and slightly high intake pressure, and SOI is similar with that of low load. In contrast, at high load, the optimal IVC timing is fixed at around 114 °CA BTDC and EGR rate is reduced to about 20%, while a late SOI (2.9 °CA ATDC) is needed to avoid overly high in-cylinder peak pressure and pressure rise rate.

The Influence of Common-rail Adjustment on the Parameters of a Diesel Tractor Engine

The article deals with the issue of high-pressure indication of a diesel tractor engine Z 1727, which was fitted with a modern electronically controlled common-rail injection system. The aim of the study is to evaluate the influence of the adjustment of the fuel system – start of injection (SOI) timings and the rail pressure (PRAIL) – on the pressure development in the cylinder (PCYL), the heat release (HR) and the combustion noise level (CNLA). Furthermore, the article examines the influence of pilot and post fuel injections on the CNLA. The experiments were conducted at constant speed (1480 rpm) with four PRAILs and different SOI timings. As the results of measurements have shown, higher rail pressure causes higher pressure and a release of a larger amount of heat in the cylinder. These two parameters are the basic prerequisite for higher engine efficiency – higher power output of the engine at lower fuel consumption and decreased production of harmful emissions. Other advantages of the common-rail fuel system include the potential of dividing the main injection dose into the pilot injection and main injection, as well as the potential post injection. The measurements have further demonstrated that including a pilot injection phase significantly contributes to a decrease in combustion noise level as well as a more even, quieter operation of the engine.

Application of Dynamic ϕ–T Map: Analysis on a Natural Gas/Diesel Fueled RCCI Engine

In this study, dynamic ϕ–T map analysis was applied to a reactivity controlled compression ignition (RCCI) engine fueled with natural gas (NG) and diesel. The combustion process of the engine was simulated by coupled kiva4-chemkin with a diesel oil surrogate (DOS) chemical mechanism. The ϕ–T maps were constructed by the mole fractions of soot and NO obtained from senkin and ϕ–T conditions from engine simulations. Five parameters, namely, NG fraction, first start of injection (SOI) timing, second SOI timing, second injection duration, and exhaust gas recirculation (EGR) rate, were varied in certain ranges individually, and the ϕ–T maps were compared and analyzed under various conditions. The results revealed how the five parameters would shift the ϕ–T conditions and influence the soot–NO contour. Among the factors, EGR rate could limit the highest temperature due to its dilute effect, hence maintaining RCCI combustion within low-temperature combustion (LTC) region. The second significant parameter is the premixed NG fraction. It could set the lowest temperature; moreover, the tendency of soot formation can be mitigated due to the lessened fuel impingement and the absence of C–C bond. Finally, the region of RCCI combustion was added to the commonly known ϕ–T map diagram.

A numerical and experimental study of dual fuel diesel engine for different injection timings

The dual-fuel technology has the potential to offer significant improvements in the CO2 emissions from light-duty compression ignition engines, and in this sense, such a concept represents a viable solution to reduce emissions from diesel engines by using natural gas as an alternative fuel. In light duty, high-speed engines, where the combustion event can be temporally shorter, the injection timing plays an important role on the performance and emissions. Following a methodology that has been proposed in previous authors' papers, this article summarizes the results of a combined numerical and experimental study on the effect of injection timing on performance and pollutant fractions of a common rail diesel engine supplied with natural gas and diesel oil. The study of dual-fuel engine carried out in this paper aims at the evaluation of the CFD potential to predict the main features of this particular technology. The experimental investigations allow the validation of the CFD modeling and, at the same time, highlight the major aspects that arise from the actual engine operation with different diesel injection advances. The fluid-dynamic calculations are extremely useful to put into evidence the key phenomena that take place during the dual-fuel operation, say the typical flame propagation throughout the premixed methane–air medium that is activated by the early self-ignition of the diesel fuel. While previous papers have discussed the effect of the NG/diesel fuel ratio, this paper focuses the attention on different conditions that have been induced by varying the injection timing at fixed brake torque and diesel amount. Actually, the start of injection timing can considerably influence the combustion development and therefore THC and NOx fractions production. Calculations making use of the fluent code have been compared with the experimental data and a comparison between full diesel and dual fuel operation has been made, in terms of performance and pollutant levels.