Early Direct Injection Research Articles

Realisation of Low Temperature Combustion in an Unmodified Diesel Engine

Heavy-duty diesel engines are an essential part of road transportation. Since viable alternatives are not expected in the short and medium term, the problematic emission characteristics of compression ignition engines have to be addressed. Low temperature combustion (LTC) is an alternative combustion method for compression ignition engines that allows low particulate matter and nitrogen oxide emissions while improving efficiency. To overcome the difficulties of market introduction, the realization of such alternative combustion methods should come with marginal engine modifications. Thus, this work investigates the possible realization of LTC in an unmodified diesel engine. LTC methods with and without injection strategy modifications were also studied to provide sufficient recommendations for other researchers. It was concluded that techniques requiring early direct injection, such as homogeneous charge compression ignition (HCCI) require a narrow cone angle injector to reduce wall impingement. It was also concluded that modulated kinetics (MK) type LTC can be easily achieved by applying a conventional injection strategy and high amounts of cooled exhaust gas recirculation. The realized MK combustion resulted in an enhanced NOx-PM trade-off and a lower peak pressure rise rate compared to normal operation.

Experimental Assessment of Genset Performance for PCCI-DI Combustion Engine

Applying the PCCI-DI combustion concept which can yield low emissions is tried for vehicular applications. However, much work has not been carried out on the genset engine which is a constant speed application. The PCCI can be achieved by various methods like port injection, late direct injection, early direct injection, and multiple direct injections to name a few. However in this case, it is achieved using the port injection. The two different port injection quantities are tried out. The first is with 3 ms pulse and the other with 5 ms pulse of port injection. In this study, PCCI-DI engine is assembled with the alternator to form a genset. The genset is tested for assessing its behavior in real-world conditions. The main trials to simulate the realworld condition are the load throw-on and load throw-off trials. The extreme case of these trials is to load the engine from no load to full load during the throw-on trials and reverse in throw-off trials. The results indicate the best performance in the case of pure DI combustion. With the use of port injection, the genset performance decorates. This is due to the fuel being injected in the port and it takes a finite time for the reaction to sudden loading and de-loading of the engine. The higher the amount of port fuel injection the higher the deterioration in response is observed. The result gives the actual performance and the response in all three combustion configurations. All three cases met the ISO 8528-5 G3 class requirements.

Analysis of the effects of lubricating oil viscosity and engine speed on piston-cylinder liner frictions in a single cylinder HCCI engine by GT-SUITE program

Engines with homogenous charge compression ignition (HCCI) are the low-temperature combustion models in which automatic oxidation reactions occur with the effect of in-cylinder pressure and heat at the end of preparation of homogenous air-fuel mixture and compression stroke within the cylinder by means of port injection or early direct injection. In-cylinder gas temperatures of such engines during the cycle are lower than conventional internal combustion engines. Therefore, they cause zero NOx and soot emissions. Moreover, the occurrence of combustion in very small crankshaft angles results in a decrease in heat losses observed in cylinder walls and an increase in thermal efficiency. Reducing mechanical friction is highly significant for increasing the effective productivity of HCCI engines. In internal combustion engines, 10% of total energy obtained from the fuel is spent on the heat emerging due to mechanical frictions. 20% of mechanical friction results from the friction occurring between piston ring and liners. In this article, frictional characteristics of compression ring (TOP) and piston skirt area have been examined for two different engine speeds and lubricants, by using technical properties of single-cylinder HCCI engine and in-cylinder pressure and temperature data obtained under full load by means of GT-SUITE software. As the increase in pressure, occurring inside the cylinder at the end of the exhaust stroke and at the beginning of intake stroke, increases ring pressure load in HCCI engines, higher level of piston ring frictions has been observed when compared to internal combustion engines with the same technical properties. Piston ring contact pressure force is a more effective parameter in terms of piston frictions, when compared to hydrodynamic pressure force. The use of lubricants with higher viscosity (SAE 10W-40) has enabled the piston to move more laterally. According to the analysis results, a maximum piston speed of 3.92 m/s for 800 rpm engine speed and 7.85 m/s for 1600 rpm engine speed has been obtained. Maximum friction power losses have been found as 63.84 W at 800 rpm engine speed and 85.91 W at 1600 rpm engine speed. Oil film thickness has obtained in the middle of the piston stroke in the intake, compression, power and exhaust strokes, respectively, 1.809, 1.674, 1.547 and 1.792 µm at 800 rpm engine speed and 1.101, 1.018, 0.932 and 1.119 µm at 1600 rpm engine speed.

Study on the ignitability of a high-pressure direct-injected methane jet using a scavenged pre-chamber under a wide range of conditions

Natural gas is a promising alternative fuel for internal combustion engines, it allows for a reduction of engine-out emissions without impairing high engine efficiencies. Although this approach is already utilized from small to large engine classes, it is almost exclusively based on the combustion of a premixed homogeneous charge. For ignition, small engines use standard spark plugs or pre-chambers, while large and lean-operated engines use pre-chambers and pilot injections. Direct high-pressure gas injection is a more recent, alternative way to operate gas engines which offers benefits compared to premixed operation such as high combustion pressures, leaner operation, easier quantity regulation, and higher compression ratios, among others. However, in contrast to diesel injection, the compression temperatures are too low for the auto-ignition of the gas jets. Therefore, an additional ignition system is required, usually a pilot injection system is used. In this study, the usability and performance of a scavenged pre-chamber used for the ignition a high-pressure gas jet has been investigated in an optically accessible test-rig that is able to operate at engine-like conditions. Results show that the turbulent hot jet generated by the pre-chamber was able to ignite the high-pressure gas jet under a wide range of operating conditions. Moreover, it also appears to be a promising ignition strategy for very early direct injection during the compression stroke as well as for port injection. The good performance is attributed to the intense mixing of the main gas jet with the hot jet exiting the pre-chamber.

Effects of control strategies for mixture activity and chemical reaction pathway coupled with exhaust gas recirculation on the performance of hydrogen-enriched natural-gas fueled spark ignition engine

The excellent physicochemical properties of the hydrogen make it a promising fuel in the clean energy systems, including engines. In this study, the performance of a heavy-duty lean-burn natural gas (NG)-fueled spark ignition (SI) engine with hydrogen addition are examined through experiments. Then, a full-size one-dimensional (1D) GT-Power simulation model of the SI engine is established, and the feasibility of the model is validated by comparing the experimental and simulation results. In addition, control strategies for mixture reactivity and chemical reaction pathway are realized by using various exhaust gas recirculation (EGR) ratios and hydrogen injection timings, which applied in this validated simulation mode. The results reveal that the in-cylinder pressure, peak heat release rate (HRR), and in-cylinder averaged temperature of the hydrogen-enriched NG-fueled SI engine decrease with the increase in the EGR ratio by using the port fuel injection (PFI), early direct injection (DI), or late DI strategy. In addition, the volumetric efficiency, combustion efficiency and NOx emissions are reduced, while the ignition delay period is prolonged with the increase of the EGR ratio if the three strategies are used. Specifically, under the same operating conditions and EGR ratio of 18%, the volumetric efficiency the NG SI engine is obtained to be 66.6% and 70.9% by using the PFI strategy and late DI strategy, respectively. Obviously, compared to the PFI strategy, the volumetric efficiency of the NG SI engine is increased by using the late DI strategy. In addition, the combustion efficiency of the NG is 92.7% by using the PFI strategy, while it is 95.4% by using the late DI strategy. This suggests that the late DI strategy is also more conducive to enhancing the combustion efficiency of the NG SI engine. Furthermore, the NOx emissions are reduced by introducing the EGR strategy due to the control of the chemical reaction pathway. Overall, compared to the PFI and early DI strategies, by adopting the late DI strategy in the simulation model of the hydrogen-enriched NG-fueled SI engine, the in-cylinder pressure, peak HRR, and in-cylinder averaged temperature can be effectively increased based on the control of the mixture reactivity.

Novel strategies to extend the operating load range of a premixed charge compression ignited light-duty diesel engine

Low-temperature combustion (LTC) is an alternative combustion mode to conventional diesel combustion (CDC) that offers a simultaneous reduction in oxides of nitrogen (NOx) and particulate matter (PM) emissions while retaining higher thermal efficiency. Premixed charge compression ignition (PCCI) is a promising LTC strategy that utilizes the early direct injection of diesel and exhaust gas recirculation (EGR) to reduce NOx and PM emissions simultaneously. A limited operating load range and high unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are the significant shortcomings to be addressed to realize PCCI as a commercially viable option. The present work aims to address these limitations based on experimental investigations carried out in a production light-duty diesel engine. An existing mechanical fuel injection system is replaced with a flexible common rail direct injection (CRDI) system to implement PCCI in the test engine. Based on initial parametric investigations, it was found that a combination of early direct injection, lower injection pressures, and EGR was deemed necessary to achieve PCCI mode in the test engine. However, the achievable load range was limited to 40% of the rated load, along with high HC and CO emissions. Novel approaches are attempted to address these limitations, including replacing diesel with diesel-gasoline blends with 30% gasoline by volume and utilizing a dual charge dilution strategy with water vapour induction and EGR. The start of fuel injection (SOI) sweeps from 30 to 70 deg. CA bTDC were performed to find optimal timing at each load condition to maximize the thermal efficiency within a stable combustion regime between a misfire and knocking. For loads above 40%, EGR in the range of 14% to 26.5% was used to bring the combustion within knock limits. By combining the proposed novel strategies, the engine operating load range could be extended from 40% to 80% of the rated load in PCCI. The NOx and soot emissions were significantly reduced up to 98.5% and 99.1%, respectively, compared to CDC. The engine brake thermal efficiency is increased by up to 1.6%. However, there was a significant penalty regarding HC and CO emissions.

Numerical Analysis of the Effects of Direct Dual Fuel Injection on the Compression Ignition Engine.

In this work, the influence of direct dual fuel injection on a compression ignition engine fueled with gasoline and diesel has been investigated. To do this, closed cycle combustion simulations have been performed. Gasoline has been supplied through port injection and early direct and late direct injection to achieve fuel stratification and emission reduction. Simulations have been done for various start of injection (SOI) timings of diesel fuel. A detailed discussion on a low temperature heat release (LTHR) mechanism has been done. Results revealed that the maximum gross indicated thermal efficiency (GITE) of 39% is obtained for port injection of gasoline mode. Direct dual fuel combustion (type 2) (DDC2) mode shows approximately 2% and 38% less GITE and oxides of nitrogen (NOx), respectively, and 40% more soot as compared to the port injection gasoline mode. DDC2 mode shows lower oxides of carbon and hydrocarbon emissions as compared to other dual fuel modes. More than 99% of combustion efficiency and less maximum pressure rise rate have been noticed in the DDC2 case. Strong LTHR and high temperature premixed combustion region have been found in advanced SOI timing cases (in DDC2). In-cylinder contours for the DDC2 case show that diesel and gasoline fuels combusted successively cause less in-cylinder temperature than that for the conventional dual fuel combustion case.

An experimental investigation on combustion and performance characteristics of supercharged HCCI operation in low compression ratio engine setting

This study investigates the effects of boost pressure on combustion and performance of an early direct injection homogenous charge compression ignition (HCCI) engine at a low compression ratio (CR). A 2.0 L, four-cylinder, four-stroke, gasoline direct injection engine was converted to operate in early direct injection HCCI mode. In addition, a supercharger unit was developed for engine boosting. The experiments were performed at different intake manifold absolute pressures (MAP) from 1.0 to 1.6 bar at different engine loads using n-heptane fuel. The effects of boost pressure were investigated on HCCI combustion and engine performance characteristics using volumetric efficiency, in-cylinder pressure, heat release rate (HRR), maximum in-cylinder pressure and gas temperature, CA50 (crank angle by which 50% of the fuel is burnt), combustion duration, apparent combustion efficiency, indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP), friction mean effective pressure (FMEP), indicated thermal efficiency (ITE), brake thermal efficiency (BTE), heat loss, exergy of heat loss, coefficient of variation of IMEP (COVIMEP), maximum pressure rise rate (MPRR) and ringing intensity (RI). The experimental results showed that high-efficiency HCCI operation is feasible at an engine compression ratio as low as 9.2 once the engine variables are properly optimized and an appropriate level of supercharging is utilized. An increase in indicated thermal efficiency was seen as boost pressure increased. In addition, combustion phasing advanced by increasing boost pressure or increasing air–fuel equivalence ratio values. Combustion events with CA50 2–3 °CA aTDC show the highest thermal efficiency especially at low boost pressure conditions. In addition, the pressure rise rate and ringing intensity increased by increasing air–fuel equivalence ratio and MAP. The test results also showed that HCCI operating range can be extended with the increase of intake manifold pressure especially at high load limits.

An experimental investigation on combustion, performance and ringing operation characteristics of a low compression ratio early direct injection HCCI engine with ethanol fuel blends

Homogenous charged compression ignition engines can be an alternative to spark ignition and compression ignition engines due to their high thermal efficiency and low exhaust emission characteristics. In this study, the effects of ethanol fuel blends on combustion, performance and ringing operation characteristics were investigated in an early direct injection homogenous charged compression ignition engine at a low compression ratio of 9.2. During the experiments, n-heptane, E10, E15 and E20 were used as test fuels. The experiments were carried out at three different intake air temperatures which are 353, 373 and 393 K, 800–1800 rpm engine speed range and 0.3–0.75 equivalence ratio range. The variations of indicated mean effective pressure, in-cylinder pressure, heat release rate, CA10, CA50, CA90, combustion duration, combustion efficiency, thermal efficiency, indicated specific fuel consumption, maximum pressure rise rate, coefficient of variation of indicated mean effective pressure, ringing intensity and combustion noise level were evaluated. The results showed that the maximum in-cylinder pressure and heat release rate decreased with the increase of ethanol fuel ratio in the mixture. The CA10, CA50 and CA90 advanced and the combustion duration shortened with the increase of the n-heptane fuel in the mixture. The coefficient of variation of indicated mean effective pressure increased with the increase of the ethanol fuel ratio in the mixture at misfiring region. The maximum pressure rise rate, ringing intensity and combustion noise level were tended to increase with the increase of the equivalence ratio at all test conditions.

Fuel-air mixing process of low pressure direct injection in a side ported rotary engine

Stratification is seen as a prominent technique for improving the performance of spark ignition engines especially at part loads. Though rotary engines have high specific power, they suffer high fuel consumption and HC emission. For this reason, direct injection methods in rotary engines have been investigated since they were introduced to the market. In this study, early direct injection in a side ported rotary engine was investigated by using CFD techniques. The aim of the study is to obtain the potential of low pressure direct injection method on mixture formation process. Geometrical model of Mazda Renesis engine that were modified as a single rotor engine for research activities was used in the modeling studies. Fuel was injected directly to the chamber from present oil hole location that has less geometrical constraints than any other location of the Renesis engine. Simulations were done for 2000 rpm which is a typical part load operation point of the engine. In numerical calculations, RNG k-ε model was used as the turbulence model; spray breakup was modeled by the Taylor Analogy Breakup (TAB) model. Flow pattern of intake air and fuel droplet distributions were investigated for a possibility of having rich mixture around spark plugs. The results showed that swirl-like motion of the side ported engine inhibits fuel spray to accumulate in the middle of the combustion chamber. Fuel droplets were driven to the counter side of the inlet wall by centrifugal force of the inlet air. This effect reduced as the swirl flow diminishes due to sweeping motion of the rotor. It is observed that the main flow in the chamber is converted to the tumble-like flow at middle and last part of the compression stroke.

SIMULATION MODELING OF A DUAL FUEL (NATURAL GAS-DIESEL) ENGINE USING EARLY DIRECT INJECTION TECHNIQUE OF NATURAL GAS

The research for alternative fuels increased rapidly to mitigate the pollution problems resulting from using conventional fuels in internal combustion engines. Natural gas (NG) appears the most promising alternative due to its low prices and availability around the world.In this paper, a two-zone, zero-dimensional (0-D) model for the simulation of dual fuel NG-diesel engine is developed to study the performance of the engine with a proposed technique of NG early direct injection. The model is composed of several sub-models that are based on semi-empirical formulas. NG is modeled as being directly injected at the beginning of the compression stroke. The model is applied to study the performance of HELWAN M-114 diesel engine using dual fuel of NG and diesel fuels as a case study.The results indicate that using NG early direct injection technique (EDI) results in increasing the volumetric efficiency and hence the brake power of the engine compared to the intake manifold induction (IMI) of NG with air through the intake manifold. The percentage increase in brake power is 8.7% at NG mass ratio in the total fuel (the supplement ratio (SR)) of 90% at full load. To evaluate the proposed technique, results obtained by varying the engine load and the SR. Results indicate that the slow burning rate of NG results in decrease in the brake thermal efficiency by 3.5% and increases in brake specific fuel consumption with a percentage of 10.2% at 90% SR and full load. However, a great advantage of increasing the SR is the reduction in NOx and soot emissions particularly at high engine loads where they were reduced with percentages of 28.6% and 86%, respectively at 90% SR and full load condition.

Potential of Early Direct Injection (EDI) for simultaneous NOx and soot emission reduction in a heavy duty turbocharged diesel engine

Early Direct Injection (EDI) in diesel engines with multiple injections has the potential to simultaneously reduce Nitrogen Oxide (NOx) and soot. The current work involved carrying out three-dimensional Computational Fluid Dynamic (CFD) simulations and engine experiments in order to evaluate EDI strategies on a heavy-duty diesel-fuelled engine operating at 25% load with the motivation to operate in Homogeneous Charge Compression Ignition (HCCI) mode. A uniformity Index (UI) parameter was defined to assess charge homogeneity. Results showed significant in-homogeneity and presence of wall-film for EDI. Simulations were conducted to assess improvement of charge homogeneity by several strategies; narrow spray included angle, injection timing, multiple injections and intake air heating. The maximum UI achieved by EDI was 0.78. Further work involved engine experimentation to assess the EDI strategy with dual injection. The first injection timing was varied from 90° to 20° Before Top Dead Center (BTDC) with cooled Exhaust Gas Recirculation (EGR) rate of 20%. The effect of EGR rate (0 to 35%) on the combustion behaviour was studied. An Optimized EDI (OptimEDI) strategy was developed which consisted of triple injections with fuel mass split ratio of 41%-45%-14% and an early first injection. This strategy gave 20% NOx and soot reduction simultaneously over the conventional Compression Ignition (CI) mode.

Effects of direct injection timing associated with spark timing on a small spark ignition engine equipped with ethanol dual-injection

Dual injection of ethanol fuel (DualEI) has been in development. DualEI has the potential in increasing the compression ratio and thermal efficiency of spark ignition engines by taking the advantages of ethanol fuel properties and the direct injection. This paper reports an experimental investigation of the effect of direct injection (DI) timing associated with spark timing on the performance of a small DualEI engine. Experiments were conducted with fixed port injection timing and varied DI timing before (early) and after (late) the intake valve closed at 3500 RPM and two load conditions. Results show that the engine performance is enhanced by early DI timing, although the variation of IMEP and indicated thermal efficiency with DI timing is not significant either with early DI timing or in most of the tested conditions with late DI timing. Only in the medium load condition when the DI timing is retarded from 80 to 60 CAD bTDC, the IMEP and thermal efficiency significantly reduced by about 16% due to the increased initial combustion duration, resulting in reduced flame speed and increased combustion instability. The results also show different effects of early and late DI timing associated with the spark timing on engine emissions. With late DI timing, the engine emissions of CO and NO increase with the advance of late DI timing and spark timing. With early DI timing, the engine emissions increase with the advance of spark timing. However, the variation of engine emissions with early DI timing is more complicated than that late.

Novel fuel injection strategies for PCCI operation of a heavy-duty turbocharged diesel engine

Towards the objective of achieving benefits of the Premixed Charge Compression Ignition (PCCI) mode in a multi-cylinder, turbocharged, common-rail, direct-injection, heavy-duty diesel engine, simulations were first conducted to assess improvement in in-cylinder charge homogeneity by several strategies. These strategies include multiple injections, Port Fuel Injection (PFI), and combination of PFI and Early Direct Injection (EDI). The maximum Uniformity Index (UI) achieved by EDI was 0.78. The PFI strategy could achieve UI of 0.95; however, majority of the fuel remained trapped in the port after valve closure. This indicated that except EDI, none of the above-mentioned strategies could help achieve the benefits of the PCCI mode. An optimized EDI (OptimEDI) strategy gave 20% NOx and soot reduction over the conventional CI mode. Although this strategy gave encouraging results, there was a need for more substantial reduction in emissions. Hence, a novel concept of utilizing Air-assisted Injection (AAI) into the air intake was employed. Experiments were carried out with AAI and combination of OptimEDI. Results with 48% Exhaust Gas Recirculation (EGR) and 5–10% of fuel injected using AAI gave substantial reduction in NOx and soot emissions at the part-load condition of the engine.

Numerical Study of a Direct Injection Internal Combustion Engine Burning a Blend of Hydrogen and Dimethyl Ether

In the reported study, various aspects of dimethyl ether/hydrogen combustion in a Reactivity Controlled Compression Ignition (RCCI) engine are numerically evaluated using Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES). Early direct injection and mixture propagation were also explored, along with peculiaritis of dimethyl ether combustion modeling. The numerical models are validated using available experimental results of a partially premixed dimethyl ether jet flames and an optically accessible internal combustion engine with direct hydrogen injection. LES showed more predictive results in modeling both combustion and mixture propagation. The same models were applied to a full engine cycle of an RCCI engine with stratified reactivity, to gain phenomenological insight into the physical processes involved in stratified reactivity combustion. We showed that 3D and turbulence considerations had a great impact on simulation results, and the LES was able to capture the pressure oscillations typical for this type of combustion.

A CFD Investigation of the Effects of Fuel Split Fraction on Advanced Low Temperature Combustion: Comparing a Primary Reference Fuel Blend and Ethanol

There is continuously growing interest in renewable biofuels for combustion engines to help reduce transportation energy consumption. In the present work, ethanol and a Primary Reference Fuel (PRF) were studied in an advanced LTC concept using CFD. A split injection strategy was used where the majority of the fuel was injected early during the intake stroke to create a well-mixed charge, while a portion of the charge was direct injected closer to ignition to induce forced thermal and equivalence ratio stratification in a strategy similar to partial fuel stratification (PFS). This way, the combustion process in LTC can be better controlled by staggering the autoignition process through mixture stratification. The unique characteristics of ethanol, such as its high latent heat of vaporization and reduced ϕ-sensitivity, result in unique features for a PFS-style advanced LTC mode, explored in this paper. A 3D CFD model with detailed chemistry was implemented in CONVERGE. The results showed that for both ethanol and PRF fuels, a split direct injection strategy lowers the peak heat release rate and elongates the combustion process compared to a single early direct injection due to the increased stratification. However, this effect was more pronounced for ethanol compared to PRF90 due to its higher latent heat of vaporization and reduced ϕ-sensitivity. For a 60%-40% split injection, the burn duration increased by 118% for ethanol and 91.6% for PRF90. The temperature, equivalence ratio, and OH mass fraction distributions illustrated that ethanol is primarily temperature-sensitive, while PRF90 shows a degree of ϕ-sensitivity in conjunction with temperature-sensitivity. The split direct injection of fuel creates an equivalence ratio and temperature distribution that are coupled due to the latent heat of vaporization of the fuel. For the PRF, these two effects are competing; whereas for the ethanol, the autoignition event is dictated by the thermal gradients since the fuel has a higher latent heat of vaporization and is not as ϕ-sensitive. Therefore, a PFS-style injection strategy is able to elongate the heat release rates more significantly with ethanol compared to a PRF.

Toward an Improvement of Natural Gas-diesel Dual Fuel Engine Operation at Part Load Condition by Detail CFD Simulation

Natural gas-diesel dual fuel combustion is a beneficial strategy for achieving high efficient and low emissions operation in compression ignition engines, especially in genset application heavy duty diesel engine at rated power. This study aims to investigate a dual fuel engine performance and emissions using premixed natural gas and early direct injection of diesel fuel. Due to the different reactivities of natural gas and diesel fuels, the mentioned dual fuel combustion is based on reactivity controlled compression igniton (RCCI) which is introduced whitin the cylinder. A six-cylinder direct injection (DI) diesel engine was properly modified to run on dual-fuel mode. Based on experimental study, comparative results are given for various operating modes; conventional diesel mode, convential dual-fuel mode, and RCCI mode; revealing the effect of combustion mode on performance and emission characteristics in a compression ignition engine. The results show that the conventional dual fuel combustion reduces nitrogen oxides (NOx) emissions but suffers from higher carbon monoxide (CO) and unburned hydrocarbon (HC) emissions in compared to conventional diesel mode at part load condition. Results of detailed assessment of different dual fuel modes with CFD model coupled with chemical kinetic mechanism reaveled that RCCI strategy led to higher combustion efficiency as well as lower HC and CO emissions compared to conventional dual fuel combustion at part load condition.

Effect of Fuel Injection Strategies on Performance and Emissions in HCCI Engines: a Review

Homogeneous charge compression ignition (HCCI) technology in internal combustion engines has improved several performance characteristics of engines. For instance, it has improved thermal efficiency and it has lowered the level of engine emissions, too. The application of this technology requires the usage of various blends of fuels, which are popularly injected into the engine using direct injection method at different timings i.e. early direct, late direct, and Single/Split (multiple) injections. This paper reviews the research that has shown that these three types of injection strategies have different impacts on the performance and on the emissions of engines with a particular interest in power output and thermal efficiency, cylinder pressure, heat release, pressure rise, combustion rate, energy consumption, combustion efficiency and brake mean effective pressure. Different researchers have applied varying methods in studying the impacts of these injection strategies, e.g. a method that involved a variation of the injection angles in investigating the rates of emissions at different injection timings. Furthermore, early direct injection timing strategy has proved to be more advantageous if compared to the other two injection timing strategies as it increases ignition delay (ID) thus resulting in the formation of a well-mixed fuel-oxidizer homogeneous mixture. Consequently, the early direct approach is recommended for usage in engines that adopt the HCCI technology.

Reaction-space analysis of homogeneous charge compression ignition combustion with varying levels of fuel stratification under positive and negative valve overlap conditions

Full-cycle computational fluid dynamics simulations with gasoline chemical kinetics were performed to determine the impact of breathing and fuel injection strategies on thermal and compositional stratification, combustion and emissions during homogeneous charge compression ignition combustion. The simulations examined positive valve overlap and negative valve overlap strategies, along with fueling by port fuel injection and direct injection. The resulting charge mass distributions were analyzed prior to ignition using ignition delay as a reactivity metric. The reactivity stratification arising from differences in the distributions of fuel–oxygen equivalence ratio ([Formula: see text]), oxygen molar fraction ([Formula: see text]) and temperature ( T) was determined for three parametric studies. In the first study, the reactivity stratification and burn duration for positive valve overlap valve events with port fuel injection and early direct injection were nearly identical and were dominated by wall-driven thermal stratification. nitrogen oxide (NO) and carbon monoxide (CO) emissions were negligible for both injection strategies. In the second study, which examined negative valve overlap valve events with direct injection and port fuel injection, reactivity stratification increased for direct injection as the [Formula: see text] and T distributions associated with direct fuel injection into the hot residual gas were positively correlated; however, the latent heat absorbed from the hot residual gas by the evaporating direct injection fuel jet reduced the overall thermal and reactivity stratification. These stratification effects were offsetting, resulting in similar reactivity stratification and burn durations for the two injection strategies. The higher local burned gas temperatures with direct injection resulted in an order of magnitude increase in NO, while incomplete combustion of locally over-lean regions led to a sevenfold increase in CO emissions compared to port fuel injection. The final study evaluated positive valve overlap and negative valve overlap valve events with direct injection. Relative to positive valve overlap, the negative valve overlap condition had a wider reactivity stratification, a longer burn duration and higher NO and CO emissions associated with reduced fuel–air mixing.

Load expansion of a dieseline compression ignition engine with multi-mode combustion

This paper presents a study on the upper load expansion and combustion characteristics of a multi-mode combustion engine with dieseline. The partially premixed compression ignition (PPCI) mode with early direct injection and late-injection low temperature combustion (L-LTC) mode with near-top dead center (TDC) direct injection are studied and compared at various loads with sweeps of injection parameters and exhaust gas recirculation (EGR) rates. A single injection strategy and a double injection strategy with small pilot ratios are tested. For both combustion modes, the criteria are set to identify the load limit of clean combustion. The NOx limit is 200ppm, and the particulate matter number limit is 100×106/cm3. The maximum pressure rise rate is lower than 0.8MPa/°, and the maximum cylinder pressure is below 16MPa. In addition, the coefficient of variation for the indicated mean effective pressure (IMEP) should be less than 3% combustion stability. The results indicate that L-LTC has a higher load limit than PPCI for all the test fuels; therefore, the upper load limit of PPCI can be increased using L-LTC. However, the thermal efficiency of L-LTC is lower than that of PPCI. Therefore, a multi-mode combustion strategy is proposed to be the best option for the whole load range. For the small to medium load range, PPCI can achieve a low emissions level and with a higher thermal efficiency than L-LTC; therefore, PPCI is an ideal choice for this range. For the medium to high load range, the L-LTC mode is the only suitable mode due to its low emissions. In the high load range, a simultaneous reduction in NOx and PM is not possible for both PPCI and L-LTC; therefore, the conventional CI mode has to be used to ensure high fuel economy performance.