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Past experimental studies conducted by the current authors on a 13 liter 16.7:1 compression ratio heavy-duty diesel engine have shown that diesel-Compressed Natural Gas (CNG) Reactivity Controlled Compression Ignition (RCCI) combustion targeting low NOx emissions becomes progressively difficult to control as the engine load is increased. This is mainly due to difficulty in controlling reactivity levels at higher loads. For the current study, CFD investigations were conducted in CONVERGE using the SAGE combustion solver with the application of the Rahimi mechanism. Studies were conducted at a load of 5 bar BMEP to validate the simulation results against RCCI experimental data. In the low load study, it was found that the Rahimi mechanism was not able to predict the RCCI combustion behavior for diesel injection timings advanced beyond 30 degCA bTDC. This poor prediction was found at multiple engine speed and load points.

Interest in natural gas as a fuel for light-duty transportation has increased due to its domestic availability and lower cost relative to gasoline. Natural gas, comprised mainly of methane, has a higher knock resistance than gasoline making it advantageous for high load operation. However, the lower flame speeds of natural gas can cause ignitability issues at part-load operation leading to an increase in the initial flame development process. While port-fuel injection of natural gas can lead to a loss in power density due to the displacement of intake air, injecting natural gas directly into the cylinder can reduce such losses. A study was designed and performed to evaluate the potential of natural gas for use as a light-duty fuel. Steady-state baseline tests were performed on a single-cylinder research engine equipped for port-fuel injection of gasoline and natural gas, as well as centrally mounted direct injection of natural gas.

Dual fuel (CI) engines provide an excellent means of maintaining high thermal efficiency and power while reducing emissions, particularly in situations where the primary fuel does not exhibit good auto-ignition characteristics. This is especially true of diesel engines operating on natural gas; usually in stationary applications such as distributed power generation. However, because two fuels are needed, the reliability of the engine is compromised. Therefore, this paper describes the first phase of a project that is to eventually manufacture dimethyl ether (DME) from natural gas and supply it to the pilot injector of a dual fuel engine. A chemical pilot plant has been built and operated, demonstrating an intermediate step in the production of DME from natural gas. DME is manufactured from methanol for pilot injection into a dual fuel engine operating with natural gas as the main fuel.

Lean burn operation is often used for improving the efficiency of SI engines. However, as a draw back, this method leads to a higher emissions of Unburned Hydro-Carbons, UHC, compared to stoichiometric combustion. In order to gain a better understanding of what is causing the higher UHC emission at lean burn condition, engine experiments have been carried out on a four-cylinder natural gas fueled SI engine. The concentration of UHC in the exhaust manifold and the HC concentration in the vicinity of the spark plug have been measured during the experiments using a Fast Response FID (FFID) analyzer. Using a model describing the outflow from the cylinder during the exhaust stroke and the measured UHC concentration in the manifold near the exhaust valve, the UHC emissions from the individual cycles have been determined. The investigation showed that under lean burn conditions, cycle by cycle variation had a significant importance on the total UHC emission from the engine.

Engine experiments have been conducted on a gas fueled SI engine. The engine was fueled with natural gas and mixtures of natural gas and hydrogen containing producer gas in order to examine the effect of addition of producer gas on the combustion process and the engine-out emissions. The experiments showed that addition of producer gas decreased the UHC emission at conditions leaner than λ=1.40. The CO emission was increased by addition of producer gas. This was mainly caused by unburned fuel CO from the producer gas. No effect of producer gas on the NOx emission was detected. Formaldehyde, which is suspected to cause odor problems from natural gas fired engine based power plants, was measured using FTIR. The investigation showed that the formaldehyde emission was decreased significantly by addition of producer gas to natural gas.

In-cylinder post flame oxidation of unburned hydrocarbons from crevices in a lean burn spark ignition engine has been examined for natural gas and mixtures of natural gas and a hydrogen containing producer gas. For this purpose a model was developed to describe the mixing of cold unburned reactants from crevices and hot burned bulk gas and to describe the oxidation of the unburned fuel. The post oxidation was described by a single step chemical reaction mechanism instead of detailed chemical kinetics in order to reduce the calculation time. However, the exploited Arrhenius expressions used to describe the chemical reactions were deduced from a detailed reaction mechanism. Different detailed reaction mechanisms were compared with results from combustion reactor experiments. Experiments and simulations were compared at different pressures and excesses of air similar to the conditions present during in-cylinder post oxidation.

A model process to produce dimethylether (DME) from natural gas (NG) was simulated in a one-pass mode (no material recycle), assuming steady-state and chemical and physical equilibrium. NG conversion to synthesis gas (syngas) via steam reforming resulted in stoichiometric numbers of 2.97 along with vapor mole fraction extremes for carbon dioxide, methane, and water. These concentrations formed an eight-trial simulation grid of syngas compositions. Simulation of DME production was performed in a dual reactor configuration with methanol formation as the intermediate compound. Solutions resulting from the subsequent adiabatic dehydration of the methanol-rich phase showed a consistent DME composition (88%). The resulting solutions and unreacted syngas streams from simulation were examined for applicability to a dual-fuel NG/DME CI engine.

The increased availability of natural gas (NG) in the United States (US) and its relatively low cost versus diesel fuel has increased interest in the conversion of medium duty (MD) and heavy duty (HD) engines to NG fueled combustion systems. The aim for development for these NG engines is to realize fuel cost savings and increase operating range while reduce harmful emissions and maintaining durability. Traditionally, port-fuel injection (PFI) or premixed NG spark-ignited (SI) combustion systems have been used for light duty LD, and MD engines with widespread use in the US and Europe [1]. However, this technology exhibits poor thermal efficiency and is load limited due to knock phenomenon that has prohibited its use for HD engines. Spark Ignited Direct Injection (SIDI) can be used to create a partially stratified combustion (PSC) mixture of NG and air during the compression stroke.

A diesel piloted natural gas engine's performance varies depending on operating conditions and has performed best under medium to high loads. It can often equal or better the fuel conversion efficiency of a diesel-only engine in this operating range. This paper presents a study performed on a multi-cylinder Cummins ISB 6.7L diesel engine converted to run stoichiometric natural gas/diesel micro-pilot combustion with a maximum diesel contribution of 10%. This study systematically quantifies and ranks the sensitivity of control factors on combustion and performance while operating at medium loads. The effects of combustion control parameters, including the pilot start of injection, pilot injection pressure, pilot injection quantity, exhaust gas recirculation, and global equivalence ratio, were tested using a design of experiments orthogonal matrix approach.

A thermodynamic analysis based on a pressure-time history measured during the combustion in a SI engine is a commonly used tool used for analyzing the combustion process. Both one-zone and two-zone models have been applied for this purpose. One of the major sources of the emission of unburned hydrocarbons from SI engines is the presence of crevices in the combustion chamber where a part of the unburned fuel-air mixture is trapped during the compression and the combustion. In this paper a three-zone heat release model including the effect of crevices is presented. The model is based on a thermodynamic analysis of three connected zones consisting of burned gas, unburned gas and gas trapped in crevices. Engine experiments have been carried out on a natural gas SI engine. The results from these experiments have been analyzed by the model.

Experimental investigations with a combustion bomb have been carried out with mixtures of methane and producer gas produced by thermal gasification of biomass. The investigations showed that the lamin ar flame speed increased and the amount of UHC decreased for increasing amount of producer gas in the fuel. Application of mathematical models for calculations of quench distances near the bomb walls and post oxidation reactions has led to the conclusion that the amount of unburned fuel is reduced primarily due to a promotion of post oxidation processes. Engine experiments have been carried out applying mixtures of natural gas and gasification gas as fuel for different air-fuel ratios. These investigation showed that substituting 16% (Vol.) of the natural gas by producer gas resulted in a decrease of 50% (Vol.) of the UHC from the combustion for lean mixtures.

The increased availability of natural gas (NG) in the United States (US) and its relatively low cost compared to diesel fuel has heightened interest in the conversion of medium duty (MD) and heavy duty (HD) engines to NG fueled combustion systems. The aim for development for these NG engines is to realize fuel cost savings and reduce harmful emissions while maintaining durability. Transforming part of the vehicle fleet to NG is a path to reduce dependence on crude oil. Traditionally, port-fuel injection (PFI) or premixed NG spark-ignited (SI) combustion systems have been used for MD and HD engines with widespread use in the US and Europe. But this technology exhibits poor cycle efficiency and is load limited due to knock phenomenon. Direct Injection of NG during the compression stroke promises to deliver improved thermal efficiency by avoiding excessive premixing and extending the lean limits which helps to extend the knock limit.

The increased availability of natural gas (NG) in the United States (US), and its relatively low cost compared to diesel fuel has heightened interest in the conversion of medium duty (MD) and heavy duty (HD) engines to NG fueled combustion systems. The aim is to realize fuel cost savings and reduce harmful emissions, while maintaining durability. This is a potential path to help the US reduce dependence on crude oil. Traditionally, port-fuel injection (PFI) or premixed NG spark-ignited (SI) combustion systems have been used for MD and HD engines with widespread use in the US and Europe; however, this technology exhibits poor cycle efficiency and is load limited due to knock phenomenon. Direct Injection of NG during the compression stroke promises to deliver improved thermal efficiency by avoiding excessive premixing and extending the lean limits which helps to extend the knock limit.

The increased availability of natural gas (NG) in the United States (US) and its relatively low cost compared to diesel fuel has heightened interest in the conversion of medium duty (MD) and heavy duty (HD) diesel engines to NG fuel and combustion systems (compressed or liquefied). The intention is to realize fuel cost savings and reduce harmful emissions, while maintaining or improving overall vehicle fuel economy. This is a potential path to help the US achieve energy diversity and reduce dependence on crude oil. Traditionally, port-injected, premixed NG spark-ignited combustion systems have been used for medium and heavy duty engines with widespread use in the US and Europe. But this technology exhibits poor cycle efficiency and is load limited due to knock phenomenon. Direct Injection of NG during the compression stroke promises to deliver improved thermal efficiency by avoiding premixing and extending the lean limits which helps to extend the knock limit.

Experiments have been conducted on a gas fueled spark ignition engine using natural gas and two hydrogen containing fuels. The hydrogen containing fuels are Reformulated Natural Gas (RNG) and a mixture of 50% (Vol.) natural gas and 50% (Vol.) producer gas. The producer gas is a synthetic gas with the same composition as a gas produced by gasification of biomass. The hydrocarbon emission, measured as the percentage of hydrocarbons in the fuel, which passes unburned through the engine, was for the mixture of natural gas and producer gas up to 50% lower than the UHC emissions using natural gas as fuel. The UHC emission from the experiments using reformulated natural gas was 15% lower at lean conditions. Furthermore, both hydrogen-containing fuels have a leaner lean burn limit than natural gas. The combustion processes from the experiments have been analyzed using a three-zone heat release model, which is taking the effect of crevices into account.

The medium and heavy-duty powertrain industry trend is to reduce reliance on diesel fuel and is aligned with continued efforts of achieving ultra-low emissions and high brake efficiencies. Compression Ignition (CI) of late cycle Directly Injected (DI) Natural Gas (NG) shows the potential to match diesel performance in terms of brake efficiency and power density, with the benefit of utilizing a lower carbon content fuel. A primary challenge is to achieve stable ignition of directly injected NG over a wide engine speed and load range without the need for a separate ignition source. This project aims to demonstrate the CI of DI NG through experimental studies with a Single Cylinder Research Engine (SCRE), leading to the development of a mono-fueled NG engine with equivalent performance to that of current diesel technology, 25% lower CO2 emissions, and low engine out methane emissions.