Apparent Heat Release Research Articles

Experimental study of NOx reduction on a medium speed heavy duty diesel engine by the application of EGR (exhaust gas recirculation) and Miller timing

Emission legislation that applies to engines used in shipping, rail and land power generation becomes increasingly strict. E.g. IMO Tier III applicable to sea-going vessels limits the NOx emission by 75% compared to IMO Tier II. Attaining these without sacrificing fuel consumption is a big challenge. This paper reports on engine internal measures that can provide a viable alternative to expensive (running costs) and bulky after-treatment. EGR (exhaust gas recirculation) and early intake valve closing as NOx reduction techniques are mature technologies on automotive applications but on medium speed diesel engine as investigated here, these are still not straightforward to implement. Two camshaft configurations are considered under EGR operation. In this research, a new approach for determining the EGR rate is developed. The effects of various EGR rates on fuel consumption and engine-out emissions are investigated, while in-cylinder pressure measurements and calculated AHRR (apparent heat release rates) provide more insight into the physical effects of EGR on the combustion.

The Influence of Injection pressure on Combustion and Emission Characteristics of a common-rail HSDI Diesel Engine

The present work investigates the influence of fuel injection pressure on the combustion and emission characteristics of ultra-low diesel fuel for high speed direct injection ( HSDI) diesel engine at different fuel injection timings( -12,-9,-6,-3,0 ) ATDC has been made . The fuel injection pressure were(800,1000,1200) bar and at high load ( 80Nm= 5BMAP) , low load ( 40Nm=2.5BMAP ) , With constant engine speed ( 1500rpm) . In-cylinder pressure was measured and analyzed using LABVIWE program .A calculation program specially written in MATLAB software was used to extract the apparent heat release rate, the ignition delay, combustion duration and specifies the amount of heat released during the premixed and diffusion combustion phases ( premixed burn fraction PMBF) and ( diffusion burn fraction DBF). The influence of injection pressure on the exhaust emissions such as carbon monoxide (CO), total hydrocarbons (THCs), nitric oxides (NOx), smoke number (SN) and fuel consumption were also investigated.A result referring to that when the injection pressure was increased, the ignition delay reduced. A shorter ignition delay at high injection pressure also advanced the combustion, and increased the in-cylinder pressure, heat release rate and their peaks respectively .The premixed burn fraction increased with fuel injection pressure increasing, and this caused a decrease in each of the exhaust SN, THC and CO emissions but the NOx emissions increased.

An investigation of diesel–ignited propane dual fuel combustion in a heavy-duty diesel engine

This paper presents a detailed experimental analysis of diesel–ignited propane dual fuel combustion on a 12.9-l, six-cylinder, production heavy-duty diesel engine. Gaseous propane was fumigated upstream of the turbocharger air inlet and ignited using direct injection of diesel sprays. Results are presented for brake mean effective pressures (BMEP) from 5 to 20bar and different percent energy substituted (PES) by propane at a constant engine speed of 1500rpm. The effect of propane PES on apparent heat release rates, combustion phasing and duration, fuel conversion and combustion efficiencies, and engine-out emissions of oxides of nitrogen (NOx), smoke, carbon monoxide (CO), and total unburned hydrocarbons (HC) were investigated. Exhaust particle number concentrations and size distributions were also quantified for diesel–ignited propane combustion. With stock engine parameters, the maximum propane PES was limited to 86%, 60%, 33%, and 25% at 5, 10, 15, and 20bar BMEPs, respectively, either by high maximum pressure rise rates (MPRR) or by excessive HC and CO emissions. With increasing PES, while fuel conversion efficiencies increased slightly at high BMEPs or decreased at low BMEPs, combustion efficiencies uniformly decreased. Also, with increasing PES, NOx and smoke emissions were generally decreased but these reductions were accompanied by higher HC and CO emissions. Exhaust particle number concentrations decreased with increasing PES at low loads but showed the opposite trends at higher loads. At 10bar BMEP, by adopting a different fueling strategy, the maximum possible propane PES was extended to 80%. Finally, a limited diesel injection timing study was performed to identify the optimal operating conditions for the best efficiency-emissions-MPRR tradeoffs.

Combustion and emissions characteristics of Diesel and soybean biodiesel over wide ranges of intake pressure and oxygen concentration in a compression–ignition engine at a light-load condition

The objective of this study is to understand the effects of intake pressure and intake oxygen concentration on combustion and emissions of ultra-low sulfur diesel (“Diesel”) and 100% soybean methylene ether biodiesel (“B100”) and investigate on the low-temperature combustion (LTC) regime that has a potential to simultaneously reduce nitric oxides (NOx) and soot emissions. The present study is an experimental investigation with a 1-liter single-cylinder direct-injection diesel engine. Engine experiment was conducted under intake pressures and oxygen concentrations of 100–250kPa absolute and 5–19% by volume (vol%), respectively.Thermal efficiency and carbon monoxide (CO) contour maps revealed two distinctive regions divided at an intake oxygen level of 8vol% (or an equivalence ratio of 0.85). In the oxygen-sufficient region intake pressure exhibited dominant impacts on combustion duration, stability, and thermal efficiency. The NOx–soot contour map clarifies the location and size of the “soot barrier” in Diesel, which was not observed in B100. B100 achieved simultaneous NOx and soot reduction to 0.2g/kWh and 0.1 filter smoke number (FSN), respectively, at 150kPa intake pressure with 11vol% intake oxygen concentration. Corresponding thermal efficiency was approximately 43%. Increased intake pressure over 150kPa lowered thermal efficiency at the maximum brake torque (MBT) timing. The apparent net heat release rate traces indicated that most heat release event occurred before top dead center (TDC) and burn duration was elongated when intake pressure was above 150kPa.

Determination of specific heat ratio and error analysis for engine heat release calculations

The burnt fraction f of Wiebe equation has been shown to be dependent only on the newly defined parameter ‘combustion burn factor (Ci)’; and the benefits of expressing heat release rate with respect to Ci have been presented. The errors associated with the determination of apparent heat release rate (Ahrr) and the cumulative heat release (Cum.Hrr) from the measured cylinder pressure data and the assumed specific heat ratio (γ) was determined and compared. The γ affected the calculated Ahrr more than the cylinder pressure. Overestimation of γ resulted in an underestimation of the peak value of the Ahrr and vice versa, this occurred without any shift in the combustion phasing. A new methodology has been proposed to determine the instantaneously and mean value of γ for a given combustion. This new methodology has been applied to determine γ for a wide range of engine operating conditions and for different fuels.

Accelerometer-Based Combustion Metrics Reconstruction With Radial Basis Function Neural Network for a 9 L Diesel Engine

Accelerometer-based combustion sensing in diesel engines has the potential of providing feedback for combustion control to reduce fuel consumption and engine emissions at a lower cost than in-cylinder pressure sensors. In this work, triaxial block-mounted accelerometers were used to measure the engine vibration, and pressure transducers were installed to measure the in-cylinder pressure. The in-cylinder pressure can be further utilized to compute combustion metrics, including the apparent heat release rate (AHR). Engine tests were conducted for various speeds, torques, and start of injections, on a 9 L in-line six-cylinder diesel engine equipped with a common rail high pressure injection system. The relationship between engine block acceleration and AHR was modeled using a radial basis function neural network (RBFNN). By inputting the accelerometer signal to the fixed network, AHR and other combustion metrics were estimated. As the primary concern for radial basis network training is the hidden layer weight vector selection, two algorithms for weight vector selection (modified Gram–Schmidt orthogonalization and principal component analysis) were evaluated by examining the robustness of the resulting network. One-third of the conducted tests were utilized to train the network. The network was then applied to estimate the AHR for the remaining validation tests which were not used to train the network. Comparisons were made based on the combustion metrics estimation results and the selection efficiency among the two weight vector selection methods and the random selection method. Moreover, the capability concerning the network's tolerance for additive noise was also investigated. Results confirmed that the modified Gram–Schmidt method achieved much more accurately estimated combustion metrics with the highest efficiency. On the basis of this study, a real-time closed-loop control strategy was proposed with the feedback provided based on the application of the trained RBFNN.

Modelling of soot formation in a heavy-duty diesel engine with conditional moment closure

This study presents the first application of a multidimensional conditional moment closure (CMC) combustion with a two-equation soot model to study the evolution of in-cylinder soot in diesel engines. Five high-fidelity reference cases from an optically accessible heavy-duty diesel engine were used to validate the model predictions; these include two high-temperature cases and two low-temperature cases with two different injection timings and one low-temperature case with a split injection strategy. Simulation results have been compared with experimental data by means of non-reactive fuel vapour distribution, apparent heat release rates (AHRR), temporal evolutions of quantitative in-cylinder soot mass and natural luminosity. The model was capable to reproduce semi-quantitative trends of soot mass for all five cases. In particular for low-temperature conditions the evolution of soot formation and oxidation is very well captured. A line-of-sight transformation of the computed 3Dsoot is proposed to ensure a consistent comparison with the measured 2Dsoot natural luminosity images. With this methodology additional effects related to radiation adsorption were observed. Evolutions of line-of-sight soot natural luminosity were qualitatively very well reproduced. Overall the findings suggest that the presented two-equation soot model implemented in the CMC framework is a highly promising candidate for predicting time evolutions of in-cylinder soot for diesel engines operating in different combustion modes.

Predicting In-Cylinder Soot in a Heavy-Duty Diesel Engine for Variations in SOI and TDC Temperature Using the Conditional Moment Closure Model

Numerical simulations of in-cylinder soot evolution in the optically accessible heavy-duty diesel engine of Sandia National Laboratories have been performed with the multidimensional conditional moment closure (CMC) model using a reduced n-heptane chemical mechanism coupled with a two-equation soot model. Simulation results are compared to the high-fidelity experimental data by means of pressure traces, apparent heat release rate (AHRR) and time-resolved in-cylinder soot mass derived from optical soot luminosity and multiple wavelength pyrometry in conjunction with high speed soot cloud imaging. In addition, spatial distributions of soot relevant quantities are given for several operating conditions.

Effects of ambient oxygen concentration on biodiesel and diesel spray combustion under simulated engine conditions

This study investigates the effect of ambient oxygen concentration on biodiesel and diesel spray combustion under simulated compression-ignition engine conditions in a constant-volume chamber. The apparent heat release rate (AHRR) is calculated based on the measured pressure. High-speed imaging of OH* chemiluminescence and natural luminosity (NL) is employed to visualize the combustion process. Temporally and spatially resolved NL and OH* contour plots are obtained. The result indicates that AHRR depends monotonically on the ambient oxygen concentration for both fuels. A lower oxygen concentration yields a slower AHRR increase rate, a lower peak AHRR value, but a higher AHRR value during the burn-out stage when compared with higher ambient oxygen concentration conditions. OH* chemiluminescence and NL contours indicate that biodiesel may experience a longer premixed-combustion duration. The 18% ambient O2 condition works better for biodiesel than diesel in reducing soot luminosity. With 12% O2, diesel combustion is significantly degraded. However, both fuels experience low temperature combustion at 10% O2. These results may imply that biodiesel is able to achieve the desired lower soot production under a moderate oxygen level with higher combustion efficiency, while diesel needs to be burned under very low ambient oxygen concentration for low soot production.

Detailed characterization of diesel-ignited propane and methane dual-fuel combustion in a turbocharged direct-injection diesel engine

This paper presents an experimental analysis of dual-fuel combustion based on the performance, emissions, and in-cylinder combustion measurements with gaseous propane or gaseous methane as the primary fuel and diesel as the pilot fuel. Two different sets of experiments were performed on a 1.9 litre four-cylinder engine at a constant engine speed of 1800 r/min: first, constant-pilot-quantity experiments, allowing the primary fuel concentration and the brake mean effective pressure to vary; second, constant-brake-mean-effective-pressure experiments, allowing the percentage energy substitution of the primary fuel and the pilot quantity to vary. In the constant-pilot-quantity experiments, the apparent heat release rate profiles showed the influence of the preignition chemistry and gaseous fuel burn rates on the dual-fuel combustion phasing and duration, the fuel conversion efficiency, and the engine-out emissions. With a fixed pilot quantity, the nitrogen oxide emissions were either reduced or unaffected while the smoke levels were increased or unaffected with increasing primary fuel concentration. The carbon monoxide and total unburned hydrocarbon emissions decreased and the fuel conversion efficiency increased as the pilot quantity or the primary fuel concentration was increased. Overall, diesel–propane combustion yielded higher carbon monoxide emissions, lower total unburned hydrocarbon emissions, and slightly higher fuel conversion efficiencies than diesel–methane combustion did. In the constant-brake-mean-effective-pressure experiments, at a brake mean effective pressure of 2.5 bar, diesel–propane and diesel–methane combustion behaved very similarly, the primary differences being in the preignition chemistry and the ignition delay trends. At a brake mean effective pressure of 2.5 bar, the nitrogen oxide and smoke emissions were simultaneously reduced while the carbon monoxide and total unburned hydrocarbon emissions were increased. At a brake mean effective pressure of 10 bar (a baseline diesel fuel conversion efficiency of 38%), diesel–propane fueling was prone to rapid earlier combustion while diesel–methane combustion was slower. For diesel–methane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency decreased to 37.1% as the percentage energy substitution was increased to 51%. For diesel–propane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency increased to 39% as the percentage energy substitution was increased to 46%. At high-brake-mean-effective-pressure–high-percentage-energy-substitution and large-pilot-quantity–high-equivalence-ratio conditions, diesel–propane combustion showed an apparent departure from the classical three-phase dual-fuel combustion to a distributed volumetric combustion process that resembled a “diesel-regulated homogenous-charge-compression-ignition-like” combustion process.

Evaluation of Peanut Fatty Acid Methyl Ester Sprays, Combustion, and Emissions, for Use in an Indirect Injection Diesel Engine

The paper provides an analysis of 100% peanut fatty acid methyl esters (FAMEs) and peanut FAME/ULSD#2 blends (P20, P35, and P50) in an indirect injection (IDI) diesel engine (for auxiliary power unit applications) in comparison to ultralow sulfur diesel no. 2 (ULSD#2) at various speeds and 100% load. From the fuel thermal and physical properties, it was determined that up to 50% peanut FAMEs blended with ULSD#2 (P50) would meet the ASTM D6751 fuel standard for viscosity. The ignition delay was in the range of 1 ms, and the apparent heat release presented similar values for all investigated fuels. The maximum cylinder instantaneous gas combustion temperature reached about 2100 K while the total heat flux was 1.95 MW/m2, and it was found that there was a 7% average increase in brake specific fuel consumption for P50 over ULSD#2. The mechanical efficiency for ULSD#2 and all of the tested FAMEs was around 77%, with 10% loss in overall engine efficiency for FAMEs compared with ULSD#2. Nitrogen oxide (NOx) emis...

Characterization of the effect of fatty ester composition on the ignition behavior of biodiesel fuel sprays

The effect of fatty ester composition on the combustion behavior of biodiesel fuel sprays is investigated for soy-based methyl esters, canola-based methyl esters and canola-based butyl esters. The purpose of this study is to aid fuel engineering efforts by identifying molecular structure features of biodiesel which can influence the compression ignition process during direct biodiesel utilization in diesel engines. Combustion behavior is classified through ignition delays and maximum apparent heat release rates measured in a rapid compression machine, and these measurements have been taken at the low temperatures (676–815K) and reduced oxygen concentrations (12% and 18%) corresponding to the low temperature combustion regime of advanced diesel engines. Ignition delay measurements show that the appearance of first heat release from the fuels is decreasingly sensitive to oxygen concentration as the reaction zone temperature is increased. Growth in the ester alkoxy chain length from one to four carbon atoms had minimal effect on the ignition delay. For tests in 12% oxygen, the increased polyunsaturated of soy methyl esters relative to canola methyl esters leads to longer ignition delays. This is not observed using 18% oxygen where physical transport processes are more important. The canola butyl esters exhibited the largest peak values for heat release rates, with the distinction becoming clear at reaction zone temperatures above 750K. Normalization on ignition delay and input energy bases indicates that variation of the maximum apparent heat release rates among the fuels is primarily due to unique mixing times and fuel heating values.

Ethanol utilisation in a diesel engine using dual-fuelling technology

Renewable feedstocks and high octane rating make ethanol a promising alternative fuel. In contrast to the conventional approach of applying ethanol-gasoline blends in spark-ignition engines, this study investigates the potential of ethanol fuelling in a diesel engine to achieve higher efficiency. Experiments are performed using a single-cylinder version of a common-rail diesel engine that is widely used in passenger cars. A dual-fuelling technology is implemented such that ethanol is introduced into the intake manifold using a port-fuel injector while diesel is injected directly into the cylinder. The main focus is the effect of ethanol energy fraction and diesel injection timing on engine efficiency and tailpipe emissions. While these two parameters are varied, in-cylinder pressure measurement and subsequent analysis of indicated mean effective pressure, apparent heat release rate, ignition delay, combustion phasing, and burn duration are performed. From the ethanol energy variation tests at fixed diesel injection timing, it is found that increased ethanol energy fraction increases the engine efficiency until the operation is limited by misfiring associated with over-retarded combustion phasing. By energy fraction, up to 60% of diesel is replaced by ethanol, which achieves 10% efficiency gain compared with diesel-only operation. Detailed analysis of the results reveals that the decreased burn duration is the primary cause for the efficiency gain, i.e. the fast burning of ethanol improves the combustion. However, the burn duration appears to increase with advancing the diesel injection timing at a fixed ethanol energy ratio despite the fact that the highest indicated mean effective pressure of 1020kPa is measured when the diesel injection timing is set at eight crank angle degrees before top dead centre, the most advanced diesel injection timing of this study. This is due to optimised combustion phasing such that the main heat release occurs near top dead centre, which outperforms the increased burn duration. Therefore, both burn duration and combustion phasing should be considered to explain trends in the indicated mean effective pressure or efficiency of dual-fuel combustion engines. The tailpipe emissions suggest that unburnt hydrocarbon, carbon monoxide and NOx emissions increase with increasing ethanol fraction, which raises a question on the advantages of utilising ethanol in a diesel engine. However, negligible smoke emissions are measured at ethanol energy ratio of 20% or higher suggesting that optimisation of these emissions would be much easier compared with conventional diesel combustion.

Combustion Phasing Effect on Cycle Efficiency of a Diesel Engine Using Advanced Gasoline Fumigation

Advanced premixed compression ignition (CI) combustion using fumigation has been shown to yield significant improvements in indicated efficiency over traditional diesel combustion strategies while simultaneously reducing engine-out soot and NOx emissions. To better interpret these findings, a breakdown of the ways in which actual performance deviates from ideal engine cycles is helpful. Nonideal combustion phasing is one cause of such deviations. In this paper, the centroid of the calculated apparent heat release rate is used to estimate an adjusted maximum possible thermal efficiency based on constant volume combustion using an effective compression ratio concept. Using these metrics, experimental engine data are evaluated from a single cylinder direct-injection diesel engine operating in premixed CI mode enabled by gasoline fumigation and a diesel pilot injection. Indicated gross cycle efficiency was found to be higher for premixed fumigation compared with a conventional diesel condition at the same load. A key finding of the work is that the peak indicated cycle efficiency for fumigated premixed CI combustion occurs with combustion phased very close to top dead center. Shorter heat release duration and lower heat losses from the cylinder are thought to be the cause of differences in cycle efficiency between conventional combustion and premixed CI fumigation modes.

Fumigation of a heavy duty common rail marine diesel engine with ethanol–water mixtures

A heavy duty common rail marine diesel engine operating with two stage injection is tested under load on a test bench with vapourised ethanol–water mixtures mixed into the inlet air at various rates. Ethanol/water mixture strengths of 93%, 72% and 45% by mass are tested. Results are presented for two engine loads at 1800rpm, with brake mean effective pressure (BMEP) 17bar and 20bar. At each test point, constant engine speed and brake torque are maintained for various rates of aqueous ethanol addition. Small increases in brake thermal efficiency are measured with moderate rates of ethanol addition at a BMEP of 20bar. Exhaust emissions of oxides of nitrogen, carbon monoxide, hydrocarbons, oxygen and carbon dioxide, and exhaust opacity are measured. CO emissions and exhaust opacity tend to increase with increased ethanol addition. NOx emissions tend to decrease with increased ethanol addition and with increased water content. Hydrocarbon emissions remain low, near the detection limit of the analyser. Cylinder pressure and the electronically controlled two stage liquid fuel injection timing are recorded with a high speed data acquisition system. Apparent heat release rate is calculated from the measured cylinder pressure. The apparent heat release rate and fuel injection timing together allow analysis of the mechanism of the combustion process with ethanol fumigation. Two stage injection involves a small pre-injection of diesel fuel to reduce early pressure rise rates in normal diesel engine combustion. Even though injection timing is retarded by the Engine Control Unit as more ethanol is added, combustion timing effectively advances due to the effect of two stage injection. Where the ethanol/air mixture strength is above the lower flammability limit at compression temperatures, the mixture is ignited by the pre-injection and begins to burn rapidly by flame propagation and/or autoignitive propagation before the main liquid fuel injection begins. This occurs for ethanol energy substitution rates greater than 30%. Two distinct peaks in heat release rate appear at the higher ethanol rates. Severe knock becomes apparent for 34% ethanol. Two stage injection may be disadvantageous in these circumstances.

A numerical study on a hydrogen assisted diesel engine

This work aims to numerically study the performance, combustion and emission characteristics of a hydrogen assisted diesel engine under various operating conditions. Simulations were performed using multi-dimensional software KIVA4 coupled with CHEMKIN. The Kelvin–Helmholtz and Rayleigh–Taylor hybrid break up model was implemented to accurately model the spray development. A detailed reaction mechanism was constructed to take into account the chemical kinetics of diesel and hydrogen, and it was validated against the experimental results with 0% of hydrogen induction. Simulation results showed that at low engine speeds, the indicated thermal efficiency, in-cylinder pressure and apparent heat release rate increased significantly with the induction of hydrogen. On the other hand, at high engine speed and high load conditions, no tangible changes on the engine performance, combustion characteristics were observed. In terms of emissions, CO and soot emissions were shown to be reduced under most of the engine operating conditions. Whereas for NOx emissions, a slight increase was observed at low engine speed of 1600 rpm.

Experimental investigations of comparative performance, emission and combustion characteristics of a cottonseed biodiesel-fueled four-stroke locomotive diesel engine

A large-bore, four-stroke, medium-speed, compression-ignition railway traction locomotive engine was fueled with cottonseed methyl ester (Biodiesel). The cottonseed methyl ester was stored for 6 months under ordinary storage conditions, and various fuel properties of this seasoned cottonseed methyl ester were evaluated. Various blends of cottonseed methyl ester (B10, B20, B50 and cottonseed methyl ester) were evaluated for engine performance, emissions and combustion characteristics of the locomotive engine compared to baseline diesel. Correlation of the fuel-injection performance parameters with the physical properties of biodiesel has been carried out. The engine was able to operate on cottonseed methyl ester without noticeable power loss. With cottonseed methyl ester, the thermal efficiency decreased marginally by 0.7% and the brake-specific energy consumption increased by 0.1 MJ/kWh at the rated power. Due to the lower calorific value of biodiesel, brake specific fuel consumption (BSFC) increased by 13.4% at eighth engine notch, nitrogen oxide emissions increased by 8% and particulate matter emissions decreased by 32% vis-a-vis mineral diesel. Nitrogen oxide emissions were found to be a function of injection timings, global oxygen/carbon ratios, time of the maximum mean in-cylinder temperatures and apparent heat release. Particulate matter emissions were found to depend on the air–fuel mixture’s oxygen/carbon ratio, fuel bound oxygen and fuel-injection pressure. The experiments were carried out to evaluate the in-cylinder pressure, heat-release rate, cumulative heat release, fuel-injection pressure, needle lift and fuel-injection velocities. Increased fuel-injection pressures (1000 bar compared to 900 bar for mineral diesel), advanced fuel-injection timings, shorter combustion duration, advanced in-cylinder pressures and higher heat-release rates were observed for biodiesel and blends. The findings of the present study have provided further insights into the combustion of biodiesel in locomotive engines.

Combustion behaviour of a heavy duty common rail marine Diesel engine fumigated with propane

This paper presents results from the testing of a heavy duty common rail marine Diesel engine with electronically controlled two stage liquid fuel injection, operating under load on a test bench with propane mixed into the inlet air at various rates. Results are presented for a range of engine loads, with brake mean effective pressure up to 22bar at 1800rpm. The electronic engine control unit is not modified and allowed to respond to the addition of propane according to its inbuilt map. This results in retarded injection timing with increased propane addition at some test points. At each test point, constant engine speed and brake torque are maintained for various rates of propane addition. Cylinder pressure and the injector activation voltage are recorded with a high speed data acquisition system. Apparent heat release rate is calculated from the measured cylinder pressure. At high rates of propane addition very high pressure rise rates and severe knock are measured. At the high brake mean effective pressure conditions tested, knock limits propane supply rates to less than 20% by energy. Small increases in thermal efficiency are indicated with moderate rates of propane addition. Exhaust emissions of NOx, CO, HC and smoke are measured. CO, HC and smoke emissions increase significantly with increasing propane addition. For high propane supply rates, two distinct peaks in heat release rate are measured. Analysis is made of the flammability of the propane–air mixtures at the elevated temperatures at the end of the compression stroke, using the modified Burgess–Wheeler Law. At propane supply rates greater than 25%, the propane–air mixture is flammable in its own right at compression temperature. The apparent heat release rate, fuel injection timing and flammability data allow analysis of the mechanism of the combustion process with propane fumigation.

Effects of injection parameters and EGR on combustion and emission characteristics of rapeseed oil and its blends in diesel engines

An attempt has been made to study and compare the combustion and emission characteristics of the rapeseed oil (RSO) and blends of 50%, 30%, 20% and 10% of RSO in diesel for different fuel injection pressures, fuel injection timing and for different percentages of EGR. The injection pressure was varied from 800bar to 1200bar, EGR percentage from 0% to 20% and the injection timing from 9° bTDC to TDC. These measurements were carried out in an automotive multi-cylinder diesel engine. The influence of these parameters on the exhaust emissions such as carbon monoxide (CO), total hydrocarbons (THCs), nitric oxides (NOx), smoke number (SN) and fuel consumption were also investigated. The in-cylinder pressure data was analysed to extract the apparent heat release rate, the ignition delay, combustion duration and the amount of heat released during the premixed and diffusion combustion phases of RSO and its blends. All these results were compared against diesel fuel under the reference engine operating conditions of 2.7bar BMEP at 1500rpm, 800bar of the injection pressure, 0% of the EGR and 9° bTDC of the injection timing. At reference engine operating conditions, the RSO and its blends resulted in a significant reduction of NOx emissions at the expense of CO, THC, SN, BSFC compared to diesel. The increase in the injection pressure lowered the soot emission but the NOx emissions for RSO and its blends resulted in higher values than diesel. The EGR and the injection timing had the potential of reducing the NOx emissions at the expense of CO, THC and SN.

An investigation of the impact of injection strategy and biodiesel on engine NOx and particulate matter emissions with a common-rail turbocharged DI diesel engine

An investigation of the impact of engine injection strategy on NOx and particulate matter (PM) emissions with biodiesel fueling was conducted with a common-rail turbocharged direct injection diesel engine at moderate speed and different load/torque conditions. The fuels included a baseline ultra low sulfur diesel fuel (ULSD) and a B40 (v/v) blend of a soybean methyl ester (SME)-based biodiesel and ULSD. Single fuel injections at start of injection timings over a range from 9° before to 3° after top dead center with different fuel injection pressures were investigated. It is found that at all load conditions, an increase of fuel injection pressure significantly increases NOx emissions, and that with the same injection strategy as the baseline diesel, biodiesel fueling increases NOx emissions. For particulate matter emissions, it is found that an increase of fuel injection pressure decreases PM emissions for all load conditions. Meanwhile, biodiesel fueling has a more significant effect on PM emissions at low load and a less significant effect at moderate to high load. For an engine running with early SOI (highest brake fuel conversion efficiency in this work), a decrease of fuel injection pressure can counter the biodiesel NOx effect while maintaining a similar or even lower level of PM emissions as ULSD. Both biodiesel fueling and the change of fuel injection pressure did not significantly affect the brake fuel conversion efficiency, but retarding the start of injection appears to decrease it. Apparent heat release analysis shows a faster and higher heat release peak with higher fuel injection pressure. With biodiesel fueling, an earlier of start of combustion can be observed for low load, but no significant difference in combustion phasing can be observed at moderate to high loads. A fuel spray, mixture stoichiometry field and lift-off length model was employed. Linear correlations between the average oxygen equivalence ratio of the fuel–air mixture at the autoignition zone near the lift-off length and brake specific NOx emissions were observed for all load conditions, regardless of fuel type. This confirms that the dominant factor that determines NOx emissions is the ignition event controlled by the oxygen equivalence ratio at the autoignition zone.