Canada’s remote communities experience harsh weather much of the year and run diesel generators 24 hours a day to provide heat and power. These generators utilize diesel fuel that is transported at great expense and generate greenhouse gas (GHG) and pollutant emissions. Meanwhile, remote communities produce organic wastes, such as wastewater and food wastes. Appropriate treatment of these wastes not only improves the community health and environment, but also generates certain amount of renewable fuels, such as biogas and/or syngas. Replacing diesel fuel by the renewable fuels generated from the waste treatment in the diesel generators can offset the use of diesel and also reduce GHG and pollutant emissions in remote communities. This paper reports an application of biogas generated from wastewater treatment to replace diesel in a small diesel generator by dual fuel engine technology. With simple modification, the biogas containing 50–95% of methane was introduced into the engine intake manifold. Tests were conducted to evaluate the effects of biogas flow rate and composition on average diesel fuel consumption and emissions of carbon dioxide (CO 2 ), carbon monoxide (CO), nitrogen oxides (NOx) and unburned hydrocarbons (HC). The results reveal that the introduction of biogas into the engine reduced the average diesel consumption. However, the reduction of average diesel consumption with increasing biogas flow rate was not linear, possibly due to the increase in HC emissions. The introduction of biogas reduced NOx emissions but increased CO emissions. A change in the composition of biogas (methane to CO 2 ratio) did not significantly affect the average diesel consumption and emissions.

Converting existing compression ignition (CI) engines to spark ignition (SI) operation can increase the use of natural gas (NG) in heavy-duty engine applications and reduce the reliance on petroleum fuels. Gas fumigation upstream of the intake manifold and the addition of a spark plug in place of the diesel injector to initiate and control the combustion process is a convenient approach for converting existing diesel engines to dedicated NG operation. Stoichiometric operation and a three-way catalytic converter can help the engine to comply with increasingly strict emission regulations. However, as the CI-to-SI conversion usually maintains the conventional geometry of a CI engine (i.e., maintains the flat cylinder head and the bowl-in piston), the goal of this study was to observe some of the effects that the diesel conversion to stoichiometric NG SI operation will have on the engine’s performance and emissions. Dynamometer tests were performed at a constant engine speed at 1300 rpm but various spark timings. The experimental results for a net indicated mean effective pressure ∼ 6.7 bar showed that ignition timing did not affect the end of combustion due to the slow-burn inside the squish. Moreover, the less-optimal conditions inside the squish led to increased carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. While the combustion event was stable with no signs of knocking at the medium load conditions investigated here, the results suggest that the engine control needs to optimize the mass fraction trapped inside the squish region for a higher efficiency and lower emissions.

Recent innovations in Metal Supported Solid Oxide Fuel Cells (MS-SOFC) have increased the longevity and reliability of fuel cells. These innovations drive the desire to create power generating systems that combine different ways of extracting power from a fuel to increase overall thermal efficiency. This investigation assesses the feasibility of operating an internal combustion engine with the anode tail-gas, which is a blend of H 2 , CO, CO 2 , H 2 O, and CH 4 , exhausted by a MS-SOFC. This engine would be used to support fuel cell balance of plant equipment and produce excess electrical power. Four variations of the expected anode tail-gas blends were determined by varying the dewpoint temperature of the fuel. Gas blends are tested by combining separate flows of each constituent, and combustion is tested using a Cooperative Fuel Research (CFR) engine. Compression ratio, spark timing, inlet manifold temperature, and boost pressure were used to obtain optimal operating conditions. Stable engine operation was obtained on all test blends. A combination of computational fluid dynamics (CFD) and analysis of chemical species and reaction mechanisms is used to develop an engine and combustion model. This model allows for further investigation into anode tail-gas combustion characteristics. Response Surface Method Optimization was used to experimentally optimize operating parameters and determine the maximum achievable efficiency utilizing the CFR engine. All test blends with H 2 O produced power in the engine although the blend with the most water content caused operational problems with the CFR engine test stand, including large amounts of water entering the oil system. Three chemical kinetic mechanisms were investigated that had the correct species for simulating the fuel with a low number of reactions to facilitate low computational time: San Diego (SD), GRI and Gallway 2017 (NUIG) mechanism. Out of these four mechanisms, the NUIG mechanism results fit the CFR engine experimental data best. Response Surface Method Optimization was performed on the most viable test blends, the steam injections blends at 40°C and 90°C fuel dewpoint temperature. During optimization the 40°C dewpoint temperature blend brake efficiency increased from 20% to 21.6%, and the 90°C dewpoint temperature blend brake efficiency increased from 17% to 22.3%.

A multidimensional computational fluid dynamics (CED) method has been used to improve the exhaust gas recirculation (EGR) distribution in the intake manifold. Since gas flow in the intake system is affected by intake pulsation caused by the gas exchange process, a pulsation flow simulation is used. A one-dimensional gas exchange calculation is combined with three-dimensional intake gas flow to simulate pulsation flow. This pulsation flow simulation makes it possible to predict the EGR distribution. The gas flow in the intake system was analyzed in detail. It was found that a reverse flow region formed downstream of the throttle valve. The size and shape of the reverse flow region greatly depend on the engine operating conditions. With a conventional EGR system, it is difficult to distribute EGR uniformly under various engine operating conditions. A new EGR system that uses a spiral flow to mix the fresh air and EGR gas has been developed to obtain a uniform EGR distribution. As a result of adopting this system, a uniform EGR distribution is obtained regardless of the engine operating conditions. This spiral flow EGR system was applied to a low-emission vehicle (LEV) put on the Japanese market.

The conversion of existing diesel engines to spark ignition (SI) operation by adding a low-pressure injector in the intake manifold for fuel delivery and replacing the original high-pressure fuel injector with a spark plug to initiate and control the combustion process can reduce U.S. dependence on petroleum imports and increase natural gas (NG) applications in heavy-duty transportation sectors. Since the conventional diesel combustion chamber (i.e., flat-head-and-bowl-in-piston-chamber) creates high turbulence, the converted NG SI engine can operate leaner with stable and repeatable combustion process. However, existing literatures point to a long late-combustion duration and increased unburned hydrocarbon emissions in such retrofitted engines that maintained the original combustion chamber. Consequently, the main objective of this paper was to report recent findings of NG combustion characteristics inside a bowl-in-piston combustion chamber that will add to the general understanding of the phenomena. The new results indicated that the premixed NG burn inside the bowl-in-piston combustion chamber will separate into a bowl-burn and a squish-burn processes in terms of burning location and timing. The slow burning event in the squish region explains the low slope of the burn rate towards the end of combustion in existing studies (hence the longer late-combustion period). In addition, the less-favorable conditions for the combustion in the squish region explained the increased carbon monoxide and unburned hydrocarbon emissions.

Upcoming CO 2 legislation in Europe is driving heavy-duty vehicle manufacturers to develop highly efficient engines more than ever before. Further improvements to conventional diesel combustion, or adopting the reactivity controlled compression ignition concept are both plausible strategies to comply with mandated targets. This work compares these two combustion regimes by performing an optimization on both using Design of Experiments. The tests are conducted on a heavy-duty, single-cylinder engine fueled with either only diesel, or a combination of diesel and gasoline. Analysis of variance is used to reveal the most influential operating parameters with respect to indicated efficiency. Attention is also directed towards the distribution of fuel energy to quantify individual loss channels. A load-speed combination typical for highway cruising is selected given its substantial contribution to the total fuel consumption of long haul trucks. Experiments show that when the intake manifold pressure is limited to levels that are similar to contemporary turbocharger capabilities, the conventional diesel combustion regime outperforms the dual fuel mode. Yet, the latter displays superior low levels of nitrogen oxides. Suboptimal combustion phasing was identified as main cause for this lower efficiency. By leaving the intake manifold pressure unrestricted, reactivity controlled compression ignition surpasses conventional diesel combustion regarding both the emissions of nitrogen oxides and indicated efficiency.

Anhydrous ammonia produced using wind power on farms can be a renewable alternative to conventional fertilizers and to fossil fuels used in engine-powered equipment. Although it has been shown that ammonia can be used in dual fuel modes in diesel engines, its inherently low flame speed results in poor combustion efficiency and thus reduces allowable diesel fuel replacement ratios. In this work, a novel method using a thermochemical recuperation (TCR) reactor system to partially decompose ammonia into hydrogen and nitrogen over a catalyst was demonstrated in diesel engine powered tractor. In the experiments, a John Deere 6400 agricultural tractor powered by a non-EPA tier-certified 4045TL diesel engine was operated in dual-fuel mode using anhydrous ammonia as the secondary fuel. Liquid ammonia from a tank was vaporized and heated using a series of heat exchangers and partially decomposed to hydrogen gas before being fumigated into the intake manifold. The catalytic TCR reactor utilized both exhaust waste heat and unburned hydrocarbon heating value to drive the ammonia decomposition process. Engine emissions and performance data were collected across a standard 8-mode test. The engine was operated using diesel only and in dual fuel mode with up to 42% replacement of diesel with ammonia on a lower heating value basis. Engine loading was accomplished using a power takeoff (PTO) dynamometer. Measured brake thermal efficiency was improved by up to 5.0% using thermochemical recuperation, and brake specific CO 2 emissions were reduced by up to 44% over diesel-only rates.

The electrification of powertrains is now the accepted roadmap for automotive vehicles. The next big step in this area will be the adoption of 48V systems, which will facilitate the use of technologies such as electric boosting and integrated startergenerators. The introduction of these technologies gives new opportunities for engine airpath design as an electrical energy source may now be used in addition to the conventional mechanical and exhaust thermal power used in super- and turbochargers. This work was conducted as part of the EU funded project “THOMSON” which aims to create a cost effective 48V system enabling engine downsizing, kinetic energy recovery, and emissions management to reduce the environmental impact of transportation. The paper presents a study on an electrified airpath for a 1.6L diesel engine. The aim of this study is to understand the design and control trade-offs which must be managed in such an electrified boosting system. A two-stage boosting system including an electric driven compressor (EDC) and a variable geometry turbocharger (VGT) is used. The air path also include low and high pressure EGR loops. The work was performed using a combination of 1D modelling and experiments conducted on a novel transient air path test facility. The simulation results illustrate the trade-off between using electrical energy from in the EDC or thermal energy in the turbocharger to deliver the engine boost pressure. For a same engine boost target, the use of the EDC allows wider VGT opening which leads to lower engine backpressure (at most 0.4bar reduction in full load situation) and reduced pumping losses. However, electricity consumed in EDC either needs to be provided from the alternator (which increases the load on the engine) or by depleting the state of charge of the battery. The location of charge air coolers (pre- or post-EDC) is also investigated. This changes the EDC intake temperature by 100K and the intake manifold by 5K which subsequently impacts on engine breathing. An experimentally validated model of a water charge air cooler model has been developed for predicting flow temperature.

Heavy-duty compression-ignition (CI) engines converted to natural gas (NG) spark ignition (SI) operation have the potential to increase the use of NG in the transportation sector. A 3D numerical simulation was used to predict how the conventional CI combustion chamber geometry (i.e., re-entrant bowl and flat head) affects the combustion stability, performance and emissions of a single-cylinder CI engine that was converted to SI operation by adding a low-pressure gas injector in the intake manifold and a spark plug in place of the diesel injector. The G-equation based 3D CFD simulation investigated three different combustion chamber configurations that changes the size of the squish region at constant compression ratio and clearance height. The results show that the different flame propagation speeds inside and outside the re-entrant bowl can create a two-zone combustion phenomenon. More, a larger squish region increased flame burning speed, which decreased late-combustion duration. All these findings support the need for further investigations of combustion chamber shape design for optimum engine performance and emissions in CI engines converted to NG SI operation.

Heavy-duty compression-ignition (CI) engines converted to natural gas (NG) operation can reduce the dependence on petroleum-based fuels and curtail greenhouse gas emissions. Such an engine was converted to premixed NG spark-ignition (SI) operation through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector. Engine performance and combustion characteristics were investigated at several lean-burn operating conditions that changed fuel composition, spark timing, equivalence ratio, and engine speed. While the engine operation was stable, the reentrant bowl-in-piston (a characteristic of a CI engine) influenced the combustion event such as producing a significant late-combustion, particularly for advanced spark timing. This was due to an important fraction of the fuel burning late in the squish region, which affected the end of combustion, the combustion duration, and the cycle-to-cycle variation. However, the lower cycle-to-cycle variation, stable combustion event, and the lack of knocking suggest a successful conversion of conventional diesel engines to NG SI operation using the approach described here.

Low-pressure exhaust gas recirculation (LP-EGR) is an EGR configuration in which clean exhaust gas is taken downstream of the turbine and aftertreatment, and then reintroduced upstream of the compressor (1) . Employing LP-EGR on Diesel engines can improve fuel economy by reducing pumping losses, lowering intake manifold temperature and facilitating advanced combustion phasing (2, 3) . The LP-EGR can also improve compressor and turbine performance by moving their operating points towards higher flow rate and higher efficiency points, which is reflected as a net reduction in pumping losses of the engine. In this study, we focus on effects of introducing LP-EGR on the compressor pressure ratio, and isentropic total-to-total efficiency. The flow field of LP-EGR and air mixing upstream of the compressor as well as the entire compressor stage were studied using a CFD RANS model. The model was validated against turbocharger gas stand measurements. A T-junction mixer was chosen as the design baseline, and various configurations of this mixer were evaluated. The impact of the geometric configuration of the mixer was studied by varying mixing length, EGR jet introduction angle, and EGR-to-air cross section area ratio over a wide range of relevant engine operating conditions. The flow field upstream of the compressor is strongly affected by the dimensionless quantity EGR-to-air momentum ratio. At intermediate momentum ratios, stream-wise counter-rotating vortex pairs (4) are induced in the flow. These vortices can reach the impeller inlet, and depending on vorticity and length scale, perturb the local velocity triangle. At low and high momentum ratios, creeping or impinging jets respectively are formed. In addition prewhirl can be induced by eccentric introduction of EGR. The EGR-induced prewhirl acts similar to an inlet guide vane and can alter the incidence angle at the impeller inlet. The performance of the compressor is altered by the EGR-induced flow field. Compressor pressure ratio is either increased or decreased depending on the direction of EGR-induced prewhirl with eccentric EGR introduction. The compressor efficiency decreases at low flow rates by introduction of concentric EGR due to perturbation of the velocity triangle at the impeller inlet. On the other hand, at low flow rates compressor efficiency can be improved by eccentric EGR introduction, which generates prewhirl in the direction of rotation of the impeller leading to improved incidence angle. The extent to which the compressor is influenced by the EGR-induced flow field is generally reduced by increasing the EGR mixing length, due to viscous damping and breakdown of large-scale EGR-induced vortices. The LP-EGR configuration provides a potential pathway towards improvement of compressor performance, not only by increasing compressor flow rate, but also by manipulation of the flow field. Given that the engine pumping losses are strongly dependent on compressor performance, specifically the compressor efficiency, this study indicates that LP-EGR provides an important path towards reducing pumping loss and improving fuel conversion efficiency.

Since the beginning of this century, Liquefied Natural Gas (LNG) has been attracting more and more attention as a cleaner energy alternative to other fossil fuels, mainly due to the possibility to transport it over longer distances than natural gas in pipelines and lower environmental impact than other liquid fuels. It is expected that this trend in the use of LNG will lead to steady increases in demand over the next few decades. At present, in the automotive sector, natural gas is employed as fuel in spark-ignited (SI) engines in the gas phase (CNG) adopting port-fuel injection system (PFI) in the intake manifold, with the main result of reducing CO 2 emissions by up to 20%, compared with gasoline operation. However, SI engines which are operated in this manner suffer loss of peak torque and power due to a reduction in volumetric efficiency. Direct-Injection (DI) inside the cylinder can overcome this drawback by injecting CNG after intake valve closure. Another strategy could be the injection of natural gas in the liquid phase, both in PFI or DI mode. The injected fuel evaporation cools down the intake air; increasing the charge density with a substantial improvement in the engine volumetric efficiency and delivered power. However, at present, injection systems dedicated to cryogenic injection of natural gas are still in the prototype state. In the present study, the volumetric efficiency and performance of a turbocharged, LNG fuelled SI-ICE were numerically analysed both in the cases of DI and PFI modes and compared with the results of a conventional CNG system. Various fuel injection timings and injector position were analysed. The engine performance was evaluated by means of a one-dimensional model developed with the simulation program GT-Power, while the verification of the LNG-air mixture characteristics was carried out with the commercial code Aspen HYSIS. The numerical activity has shown that gaseous DI, before inlet valves closing, gives the worst result since methane, once injected into the cylinder, expands hindering the entry of air. On the other side, liquid PFI represents the best configuration to maximize the volumetric efficiency and therefore the engine power. All the technological issues related to a cryogenic liquid methane injection system were not taken into consideration in this study.

A design process was defined and implemented for the rapid development of purpose-built, heavy-fueled engines using modern CAE tools. The first exercise of the process was the clean sheet design of the 1.25 L, three-cylinder, turbocharged AMD45 diesel engine. The goal of the AMD45 development program was to create an engine with the power density of an automotive engine and the durability of an industrial/military diesel engine. The AMD45 engine was designed to withstand 8000 hours of operation at 4500 RPM and 45 kW output, while weighing less than 100 kg. Using a small design team, the total development time to a working prototype was less than 15 months. Following the design phase, the AMD45 was fabricated and assembled for first prototype testing. The minimum-material-added design approach resulted in a lightweight engine with a dry weight 89 kg for the basic engine with fuel system. At 4500 RPM and an intake manifold pressure of 2.2 bar abs., the AMD45 produced 62 kW with a peak brake fuel-conversion efficiency greater than 34%. Predictions of brake power and efficiency from the design phase matched to within 5% of experimental values. When the engine is detuned to 56 kW maximum power, the use of multi-pulse injection and boost pressure control allowed the AMD45 to achieve steady state emissions (as measured over the ISO 8178 C1 test cycle) of CO and NO x +NMHC that met the EPA Tier 4 Non-road standard without exhaust after-treatment, with the exception of idle testing. PM emissions were also measured, and a sulfur-tolerant diesel particulate filter has been designed for PM after-treatment.

This paper experimentally investigates the effect of water injection in the intake manifold on a naturally aspirated, single cylinder, Gasoline Direct Injection engine to determine the combustion and emissions performance with combustion knock mitigation. The endeavor of the current study is to use water injection to attain the optimum combustion phasing without knocking. Further elevated intake air temperature tests were conducted to observe the effect of water injection with respect to combustion and emissions. Experiments were carried out at medium load condition (800 kPa NIMEP, 1500 RPM) at intake air temperatures between 30–90° C in 20° C increments. Two fuels, an 87 AKI and a 93 AKI were used in this study. Baseline tests were undertaken with the high-octane fuel (93 AKI) to achieve optimal combustion phasing corresponding to Maximum Brake Torque (MBT) without water injection. Water injection was utilized for the low octane fuel to achieve combustion phasing of 8–10° ATDC and within the controlled knock limit. Combustion phasing was achieved by controlling the ignition timing, water injection quantity and timing to the knock threshold. The results showed that water injection and the resultant charge cooling mitigates combustion knock and an optimum combustion phasing based on indicated fuel conversion efficiency is achieved with a water to fuel ratio of 0.6. Water injection reduces the NOx emissions while achieving better indicated thermal efficiency compared to the baseline tests. A detailed comparison is presented on the combustion phasing, indicated thermal efficiency, burn durations, HC, NOx and PN emissions in this paper.

The combustion in an experimental medium duty direct injected engine was investigated in a dual mode process known as partially premixed compression ignition (PPCI). Both a common rail fuel injection system and port fuel injection (PFI) system have been custom designed and developed for the experimental single cylinder engine in order to research the combustion and emissions characteristics of Fischer Tropsch synthetic paraffinic kerosene (S8) with PFI of n-butanol in a low temperature combustion mode (LTC). Baseline results in single fuel (ULSD) combustion were compared to dual fuel strategies coupling both the low and high reactivity fuels. The low reactivity fuel, n-butanol, was port fuel injected in the intake manifold at a constant 30% fuel mass and direct injection of a high reactivity fuel initiated the combustion. The high reactivity fuels are ULSD and a gas to liquid fuel (GTL/S8). Research has been conducted at a constant speed of 1500 RPM at swept experimental engine loads from 3.8 bar to 5.8 bar indicated mean effective pressure (IMEP). Boost pressure and exhaust gas recirculation (EGR) were added at constant levels of 3 psi and 30% respectively. Dual fuel combustion with GTL advanced ignition timing due to the high auto ignition quality and volatility of the fuel. Low temperature heat release (LTHR) was also experienced for each dual-fuel injection strategy prior to the injection of the high reactivity fuel. Peak in-cylinder gas temperatures were similar for each fueling strategy, maintaining peak temperatures below 1400°C. Combustion duration increased slightly in ULSD-PPCI compared to single fuel combustion due to the low reactivity of n-butanol and was further extended with GTL-PPCI from early ignition timing and less premixing. The effect of the combustion duration and ignition delay increased soot levels for dual fuel GTL compared to dual fuel ULSD at 5.8 bar IMEP where the combustion duration is the longest. NOx levels were lowest for GTL-PPCI at each load, with up to a 70% reduction compared to ULSD-PPCI. Combustion efficiencies were also reduced for dual fuel combustion, however the atomization quality of GTL compared to ULSD increased combustion efficiency to reach that of single fuel combustion at 5.8 bar IMEP.

A partially premixed combustion (PPC) approach was applied in a single cylinder diesel research engine in order to characterize engine power improvements. PPC is an alternative advanced combustion approach that generally results in lower engine-out soot and NOx emission, with a moderate penalty in engine-out unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions. In this study PPC is accomplished with a minority fraction of jet fuel injected into the intake manifold, while the majority fraction of jet fuel is delivered directly to the combustion chamber near the start of combustion (SOC). Four compression ratios (CR) were studied. Exhaust emissions plus exhaust opacity and particulate measurements were performed during the experiments in addition to fast in-cylinder combustion metrics. It was seen that as CR increased the soot threshold equivalence ratio decreased for conventional diesel combustion, however this afforded an increased opportunity for higher levels of port injected fuel leading to power increases from 5 to 23% as CR increased from 14 to 21.5. PPC allowed for these power increases (defined by a threshold opacity level of 3%) due to smaller particles (and lower overall number of particles) in the exhaust that influence measured opacity less significantly than larger and more numerous conventional diesel combustion exhaust particulates. Carbon monoxide levels at the higher PPC driven power levels were only modestly higher, although NOx was generally lower due to the overall enriched operation.

This paper presents the chemical composition, oxidation reactivity and nanostructural characteristics of particulate matter (PM) produced by a diesel engine operating with diesel/compressed natural gas (CNG) dual-fuel combustion. Raw, undiluted soot samples from pure diesel, 40% CNG, and 70% CNG (energy-based substitution rate) combustion were collected from the exhaust pipe. Engine operating conditions were held at 1200 RPM and 20 mg/cycle baseline load. For dual-fuel operation, split diesel injection (two injections) was used as the pilot, and CNG was injected into the intake manifold. First, soot oxidation reactivity was characterized using thermogravimetric analysis (TGA). Carbon, hydrogen, and nitrogen weight fractions were obtained using elemental analysis to measure soot aging. Transmission electron microscopy (TEM) was then used to determine the diameter of the spherules, and the morphology of soot agglomerates. It was found that soot reactivity increased with increasing CNG content. TEM images revealed a higher variation in particle diameter with increasing CNG substitution. High resolution TEM (HRTEM) images showed that CNG70 soot displayed features of immature soot particles. The enhanced reactivity could also be due to more active sites available in CNG soot, as well as the CNG soot being immature. Under this test condition and engine configuration, it can be concluded that the use of CNG affects the morphology and nanostructure of PM, and hence the oxidation reactivity of the soot.

Engine induced swirl improves mixing of fuel and air and at optimal values accelerates burn, improves the combustion stability and can decrease particulate matter (PM). However, swirl increases convective heat loss and cylinder charge loss and could increase nitrogen oxides (NOx) emissions. High intensity of swirl could impede flame development and increases emissions of total hydrocarbons (THC) and carbon monoxide (CO). Therefore, careful and smart selection of optimal swirl values is paramount in order to obtain beneficial impact on combustion and emissions performance. This study is conducted on a 0.5L single cylinder research engine with common rail (CR) diesel injection system, with parameters corresponding to modern engines of passenger cars. The engine has three separate ports in the cylinder head. The change of swirl ratio is defined by closing appropriate ports. There are three levels of swirl ratio under study — 1.7, 2.9 and 4.5, corresponding to low, medium and high swirl levels respectively. This study highlights the influence of intake induced swirl on combustion parameters and emissions. Assessed combustion parameters are, among others, heat release rate, cylinder pressure rise and indicated mean effective pressure. Assessed emissions are standard gaseous emissions and smoke, with emphasis on PM emissions. An engine speed of 1500 rpm was selected, which well represents common driving conditions of this engine size. Various common rail pressures are used at ambient inlet manifold pressure (without boost pressure) and at 1 bar boosted pressure mode. It is found that when the swirl level is increased, the faster heat release during the premixed combustion and during early diffusion-controlled combustion causes a quick increase in both in-cylinder pressure and temperature, thus promoting the formation of NOx. However, since swirl enhances mixing and potentially produces a leaning effect, PM formation is reduced in general. However, maximum peak temperature is lower for high swirl ratio and boosted modes due to the increase of heat transfer into cylinder walls. Furthermore, it is necessary to find optimal values of common rail pressures and swirl ratio. Too much mixing allows increase on PM, THC and CO emissions without decrease on NOx emissions in general. Common rail injection system provides enough energy to achieve good mixing during all the injection time in the cases of supercharged modes and high common rail pressure modes. Positive influence of swirl ratio is found at lower boost pressures, lower revolution levels and at lower engine loads. The results obtained here help providing a better understanding on the swirl effects on diesel engine combustion and exhaust emissions over a range of engine operating conditions, with the ultimate goal of finding optimal values of swirl operation.

Reductions of Nitrogen oxides (NOx), sulphur oxides (SOx) and carbon dioxide (CO 2 ) emissions have been acknowledged on the global level. The International Maritime Organization (IMO) has developed some mandatory or non-mandatory instruments such as codes, amendments, recommendations or guidelines to strengthen the emissions regulations on ships engaged in international voyage. However, it is difficult to meet the strengthened emissions regulations on the conventional marine diesel engines. Lean burn gas engines have been thus recently attracting attention in the maritime industry. The lean burn gas engines use natural gas as fuel and can simultaneously reduce both NOx and CO 2 emissions. On the other hand, since methane is the main component of natural gas, the slipped methane which is the unburned methane emitted from the lean burn gas engines might have a potential impact on global warming. The authors investigated on a ship installed conventional marine diesel engines and lean burn gas engines, and have proposed a C-EGR (combined exhaust gas recirculation) system to reduce the slipped methane from the gas engines and NOx from marine diesel engines. This system consists of a marine diesel engine and a lean burn gas engine, and the exhaust gas emitted from the lean burn gas engine is provided to the intake manifold of the marine diesel engine by a blower installed between both engines. Since exhaust gas from the gas engine including slipped methane, this system could reduce both the NOx from the marine diesel engine and the slipped methane from the lean burn gas engine simultaneously. This paper introduces the details of the proposed C-EGR system, and presents the experimental results of emissions and engine performance characteristics on the C-EGR system. In the experiment, the diesel engine was operated at three load conditions of 25, 50 and 75% along with the propeller load curve. In order to keep the slipped methane concentration constant, the gas engine was operated at a constant load condition of 25%. The intake exhaust gas quantity which is supplied to the diesel engine was adjusted by the blower speed. As a result, it was confirmed that the C-EGR system attained more than 75% reduction of the slipped methane in the intake gas. In addition, the NOx emission from the diesel engine decreased with the effect of the EGR system. Also the fuel consumption of the diesel engine did not increase, because of the methane combustion in the intake gas.

The noise of diesel engines is dependent upon numerous factors such as: load, speed, fuel injection strategies and fuel type, design of the piston, piston-pin and cylinder and their tolerances, bearings, valves and rocker arm clearances, and designs of the manifolds. In this study, engine sound and vibrations analysis have been conducted using two types of fueling and combustion strategies: classical ULSD combustion and the new RCCI with n -butanol injected in the intake manifold. The analyses add to the understanding of the influence of combustion characteristics’ effect on mechanical noise and vibrations throughout the engine’s operating cycle. The sound and vibration signals were both analyzed in the frequency and angle domain spectrum. Overall NVH spectrum from ULSD combustion was compared to that of RCCI with 50% by mass PFI of n -butanol (the 50% remaining ULSD fuel was directly injected). Frequency analyses were performed using the FFT and CPB methods with Bruel & Kjaer’s Pulse sound and vibrations analysis software. Angle domain analyses were performed, referencing 0 CAD as TDC in combustion. The engine tests were conducted at 1500 rpm and 4 bar IMEP. The COV of IMEP for DI ULSD and RCCI were 2.4 and 2.2, respectively. The correlations between sound, three dimensional vibration levels, and timings were found for: pressure gradients from combustion process, intake and exhaust valve actuations and gas exchange, and piston slap on the cylinder liner. The measurements were extracted and analyzed, and the results determined that virtually all the noise and vibration values pertinent to RCCI were lower than those of ULSD classical combustion.