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The possibility to operate current diesel engines in dual-fuel mode with the addition of an alternative fuel is fundamental to accelerate the energy transition to achieve carbon neutrality. The simulation of the dual- fuel combustion process with 0D/1D combustion models is fundamental for the performance prediction, but still particularly challenging, due to chemical interactions of the mixture. The authors defined a novel data-driven workflow for the development of combustion reaction mechanisms and used it to generate a dual-fuel mechanism for Ammonia and Diesel Primary Reference Fuels (DPRF) suitable for efficient combustion simulations in heavy duty engines, with variable cetane number Diesel fuels. A baseline reaction mechanism was created by merging the detailed ammonia mechanism by Glarborg et al. with reaction pathways for n- hexadecane and 2,2,4,4,6,8,8-heptamethylnonane from a well-established multi-component fuel mechanism.

We propose a novel dual-fuel combustion model for simulating heavy-duty engines with the G-Equation. Dual-Fuel combustion strategies in such engines features direct injection of a high-reactivity fuel into a lean, premixed chamber which has a high resistance to autoignition. Distinct combustion modes are present: the DI fuel auto-ignites following chemical ignition delay after spray vaporization and mixing; a reactive front is formed on its surroundings; it develops into a well-structured turbulent flame, which propagates within the premixed charge. Either direct chemistry or the flame-propagation approach (G- Equation), taken alone, do not produce accurate results. The proposed Dual-Fuel model decides what regions of the combustion chamber should be simulated with either approach, according to the local flame state; and acts as a “kernel” model for the G- Equation model. Direct chemistry is run in the regions where a premixed front is not present.

Over the years, much progress has been made in automotive vehicle technology to achieve high efficiency and clean combustion. Reactivity controlled compression ignition (RCCI) is one of the most widely studied high-efficiency, clean combustion strategies. However, complex dual-fuel injection systems and associated controls, high unburned hydrocarbon (UHC), and carbon monoxide (CO) emissions limit RCCI use in practical applications. Recently, single fuel RCCI strategies are gaining more attention as the above shortcomings are effectively addressed. Homogeneous charge with direct injection (HCDI) is a single fuel RCCI strategy that results in high thermal efficiency and lower UHC and CO emissions. In HCDI, the port-injected diesel fuel vapour and air are inducted during the intake stroke and ignited with direct-injected diesel fuel near the end of the compression stroke. However, high oxides of nitrogen (NOx) make HCDI less viable for practical applications.

Supercharging a single-cylinder diesel engine has proved to be a viable methodology to reduce engine-out emissions and increase full-load torque and power. The increased air availability of the supercharger (SC) system helps to inject more fuel quantity that can improve the engine's full-load brake mean effective pressure (BMEP) without elevating soot emissions. However, the increased inlet temperature of the boosted air and the availability of excess oxygen can pose significant challenges to contain oxides of nitrogen (NOx) emissions. Hence, it is important to investigate the potential NOx reduction options in supercharged diesel engines. In the present work, the potential of low-pressure exhaust gas recirculation (LP EGR) was evaluated in a single-cylinder supercharged diesel engine for its benefits in NOx emission reduction and impact on other criteria emissions and brake specific fuel consumption (BSFC).

In-cylinder emission control methods for simultaneous reduction of oxides of nitrogen (NOx) and particulate matter (PM) are gaining attention due to stringent emission targets and the higher cost of after-treatment systems. In addition, there is a renewed interest in using carbon-neutral biodiesel due to global warming concerns with fossil diesel. The bi-directional NOx-PM trade-off is reduced to a unidirectional higher NOx emission problem with biodiesel. The effect of water injection with biodiesel with low water quantities is relatively unexplored and is attempted in this investigation to mitigate higher NOx emissions. The water concentrations are maintained at 3, 6, and 9% relative to fuel mass by varying the pulse width of a low-pressure port fuel injector. Considering the corrosive effects of water at higher concentrations, they are maintained below 10% in the present work.

Extensive experimental investigations done over a decade in different engine types demonstrated the capability of achieving high efficiency along with low levels of oxides of nitrogen (NOx) and soot emissions with low temperature combustion (LTC) modes. However, the commercial application of LTC strategies requires several challenges to be addressed, including precise ignition timing control, reducing higher unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions. The lower exhaust gas temperatures with LTC operation pose severe challenges for after-treatment control systems. Among the available LTC strategies, Reactivity Controlled Compression Ignition (RCCI) has emerged as the most promising strategy due to better ignition timing control with higher thermal efficiency. Nevertheless, the complexity of engine system hardware due to the dual fuel injection system and associated controls, high HC and CO emissions are the major limiting factors in RCCI.

Achieving stable combustion without misfire and knocking is challenging in premixed charge compression ignition (PCCI) especially in small bore, air cooled diesel engines owing to lower power output and inefficient cooling system. In the present study, a single cylinder, air cooled diesel engine used for agricultural water pumping applications is modified to run in PCCI mode by replacing an existing mechanical fuel injection system with a flexible common rail direct injection system. An advanced start of fuel injection (SOI) and exhaust gas recirculation (EGR) are required to achieve PCCI in the test engine. Parametric investigations on SOI, EGR and fuel injection pressure are carried out to identify optimum parameters for achieving maximum brake thermal efficiency. An SOI sweep of 12 to 50 deg. CA bTDC is done and for each SOI, EGR is varied from 0 to 50% to identify maximum efficiency points. It was found that EGR helps in extending the load range from 20 to 40% of rated load.

Reactivity-Controlled Compression Ignition (RCCI) is a promising low-temperature combustion (LTC) strategy to mitigate the oxides of nitrogen (NOx) and soot emissions. However, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are much higher in RCCI compared to the conventional diesel combustion (CDC). In this present work, multiple injections of the direct-injected (DI) diesel fuel are explored as a potential method to reduce the high HC and CO emissions. Although significant research works have been done in the past on RCCI combustion in different engine types, investigations on small air-cooled diesel engines are very limited. In the present work, a production light-duty air-cooled diesel engine is modified to run in RCCI, with diesel as the high-reactivity fuel and gasoline as the low-reactivity fuel. Before modifications, the engine is run in CDC with production settings. In RCCI, experiments are initially performed with single-pulse DI.

Simultaneous reduction of oxides of nitrogen (NOx) and smoke emissions from diesel engines has always been a challenging task. In this research work, a relative comparison of diesel-water emulsion and water vapor induction methods has been made to examine NOx and smoke emissions reduction potential of a light-duty diesel engine. The water concentration was maintained at 6% of the total fuel in the emulsion and 6% of the total incoming air mass in the fumigation method. A stable diesel-water emulsion is prepared using commercially available surfactants, Span 80 and Tween 80 at 10% concentration. The stability of the emulsion was examined by visual inspection. The droplet size was quantified using dynamic light scattering technique and the emulsion was deemed stable for approximately 105 days on storage at room temperature. To generate water vapor in the intake manifold, 20 ultrasonic atomizers are utilized.

The ignition quality of a fuel is described by its cetane number. Experimental methods used to determine cetane number employ Co-operative fuel research (CFR) engine and Ignition quality tester (IQT) which are expensive, have less repeatability and require skilled operation, and hence least preferred. There are many prediction models reported, which involve number of double bonds and number of carbon atoms whose determination is not direct. Using models that relate biodiesel composition to its cetane number is limited by the range of esters involved. Hence, a model to predict cetane number of biodiesels that addresses the limitations of the existing models, without ignoring the influence of factors such as degree of unsaturation and number of carbon atoms, is needed. Fourier transform infrared spectroscopy (FTIR) could be one such method.

To comply with the stringent future emission mandates of light-duty diesel engines, it is essential to deploy a suitable combination of emission control devices like diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and DeNOx converter (LNT or SCR). Arriving at optimum size and layout of these emission control devices for a particular engine through experiments is both time and cost-intensive. Thus, it becomes important to develop suitable well-tuned simulation models that can be helpful to optimize individual emission control devices as well as arrive at an optimal layout for achieving higher conversion efficiency at a minimal cost. Towards this objective, the present work intends to develop a one-dimensional Exhaust After Treatment Devices (EATD) model using a commercial code. The model parameters are fine-tuned based on experimental data. The EATD model is then validated with experiment data that are not used for tuning the model.

Among the various Low Temperature Combustion (LTC) strategies, Homogeneous Charge Compression Ignition (HCCI) is most promising to achieve near zero oxides of nitrogen (NOx) and particulate matter emissions owing to higher degree of homogeneity and elimination of diffusion phase combustion. However, one of its major limitations include a very narrow operating load range owing to misfire at low loads and knocking at high loads. Implementing HCCI in small light duty air cooled diesel engines pose challenges to eliminate misfire and knocking problems owing to lower power output and air cooled operation, respectively. In the present work, experimental investigations are done in HCCI mode in one such light duty production diesel engine most widely used in agricultural water pumping applications. An external mixture preparation based diesel HCCI is implemented in the test engine by utilizing a high-pressure port fuel injection system, a fuel vaporizer and an air preheater.

Premixed Charge Compression Ignition (PCCI) is one of the most promising low temperature combustion (LTC) strategies to achieve near zero oxides of nitrogen (NOx) and particulate matter (PM) emissions along with higher thermal efficiency. One of the major problems in diesel PCCI is a narrow operating load range because of very early ignition and knocking combustion at higher loads owing to higher reactivity of diesel fuel. Further, low volatile diesel resist vaporization, resulting in fuel spray wall wetting and higher unburned emissions in PCCI. Thus, high reactivity and low volatility of diesel fuel make it not suitable for PCCI combustion. The present work attempts to address these limitations, by blending diesel with high volatile and low reactive fuels, viz. gasoline and butanol at 10% and 20% blend levels by volume.

Advanced low temperature combustion (LTC) modes are most promising to reduce green house gas emissions owing to fuel economy benefits apart from simultaneously reducing oxides of nitrogen (NOx) and particulate matter (PM) emissions from diesel engines. Various LTC strategies have been proposed so far and each of these LTC strategies have their own advantages and limitations interms of precise ignition control, achievable load range and higher unburned emissions. In the present work, a small single cylinder diesel engine is initially operated under conventional combustion mode at rated speed, varying load conditions to establish the base line reference data. Then, the engine is modified to operate under different LTC strategies including Homogenous Charge Compression Ignition (HCCI), Premixed Charge Compression Ignition (PCCI) and Reactivity Controlled Compression Ignition (RCCI).

Reactivity controlled compression ignition (RCCI) is one of the most promising low temperature combustion (LTC) strategies to achieve higher thermal efficiencies along with ultra low oxides of nitrogen (NOx) and particulate matter emissions. Small single cylinder diesel engines of air-cooled type are finding increasing applications in the agriculture pump-set and small utility power generation owing to their lower cost and fuel economy advantages. In the present work, a small single cylinder diesel engine is initially operated under conventional combustion mode at rated speed, varying load conditions to establish the base line reference data. Then, the engine is modified to operate under RCCI combustion mode with a newly designed cylinder head to accommodate a high pressure, fully flexible electronically controlled direct diesel fuel injection system, a low pressure gasoline port fuel injection system and an intake air pre heater.

Reactivity Controlled Compression Ignition (RCCI) has been shown to be an attractive concept to achieve clean and high efficiency combustion. RCCI can be realized by applying two fuels with different reactivities, e.g., diesel and gasoline. This motivates the idea of using a single low reactivity fuel and direct injection (DI) of the same fuel blended with a small amount of cetane improver to achieve RCCI combustion. In the current study, numerical investigation was conducted to simulate RCCI and HCCI combustion and emissions with various fuels, including gasoline/diesel, iso-butanol/diesel and iso-butanol/iso-butanol+di-tert-butyl peroxide (DTBP) cetane improver. A reduced Primary Reference Fuel (PRF)-iso-butanol-DTBP mechanism was formulated and coupled with the KIVA computational fluid dynamic (CFD) code to predict the combustion and emissions of these fuels under different operating conditions in a heavy duty diesel engine.

A novel 2-zone combustion chamber concept (patent pending) was developed using multi-dimensional modeling. At minimum volume, an axial projection in the piston divides the volume into distinct zones joined by a communication channel. The projection provides a means to control the mixture formation and combustion phasing within each zone. The novel combustion system was applied to reactivity controlled compression ignition (RCCI) combustion in both light-duty and heavy-duty diesel engines. Results from the study of an 8.8 bar BMEP, 2600 RPM operating condition are presented for the light-duty engine. The results from the heavy-duty engine are at an 18.1 bar BMEP, 1200 RPM operating condition. The effect of several major design features were investigated including the volume split between the inner and outer combustion chamber volumes, the clearance (squish) height, and the top ring land (crevice) volume.

Control of the timing and magnitude of heat release is one of the biggest challenges for premixed compression ignition, especially when attempting to operate at high load. Single-fuel strategies such as partially premixed combustion (PPC) use direct injection of gasoline to stratify equivalence ratio and retard heat release, thereby reducing pressure rise rate and enabling high load operation. However, retarding the heat release also reduces the maximum work extraction, effectively creating a tradeoff between efficiency and noise. Dual-fuel strategies such as reactivity controlled compression ignition (RCCI) use premixed gasoline and direct injection of diesel to stratify both equivalence ratio and fuel reactivity, which allows for greater control over the timing and duration of heat release. This enables combustion phasing closer to top dead center (TDC), which is thermodynamically favorable.

The focus of the present study was to characterize Reactivity Controlled Compression Ignition (RCCI) using a single-fuel approach of gasoline and gasoline mixed with a commercially available cetane improver on a multi-cylinder engine. RCCI was achieved by port-injecting a certification grade 96 research octane gasoline and direct-injecting the same gasoline mixed with various levels of a cetane improver, 2-ethylhexyl nitrate (EHN). The EHN volume percentages investigated in the direct-injected fuel were 10, 5, and 2.5%. The combustion phasing controllability and emissions of the different fueling combinations were characterized at 2300 rpm and 4.2 bar brake mean effective pressure over a variety of parametric investigations including direct injection timing, premixed gasoline percentage, and intake temperature. Comparisons were made to gasoline/diesel RCCI operation on the same engine platform at nominally the same operating condition.

In this work computational and experimental approaches are combined to characterize in-cylinder flow structures and local flow field properties during operation of the Sandia 1.9L light-duty optical Diesel engine. A full computational model of the single-cylinder research engine was used that considers the complete intake and exhaust runners and plenums, as well as the adjustable throttling devices used in the experiments to obtain different swirl ratios. The in-cylinder flow predictions were validated against an extensive set of planar PIV measurements at different vertical locations in the combustion chamber for different swirl ratio configurations. Principal Component Analysis was used to characterize precession, tilting and eccentricity, and regional averages of the in-cylinder turbulence properties in the squish region and the piston bowl.