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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.

Natural gas is a challenging fuel for HCCI engines because its single-stage ignition and rapid combustion make it difficult to optimize combustion timing over a significant load range. This study investigates direct injection of a pilot quantity of high-cetane fuel near TDC as a range extension and combustion control mechanism for natural gas HCCI engines. The EGR and load range is studied in a supercharged natural gas HCCI engine equipped with external EGR, intake heating and a direct injection system for n-heptane pilot fuel. The operating range and emissions are of primary interest and are compared between both the baseline HCCI engine with variable intake temperature and the direct injected HCCI (DI-HCCI) engine with constant intake temperature. Test results show the EGR and load range at fixed intake temperature can be extended using pilot direct injection.

A physics-based control-oriented model is developed to dynamically predict cycle-to-cycle combustion timing in transient fueling conditions for Homogeneous Charge Compression Ignition (HCCI) engines. The model simulates the engine cycle from the intake stroke to the exhaust stroke and includes the thermal coupling dynamics caused by the residual gases from one cycle to the next cycle. A residual gas model, a modified knock integral model, a fuel burn rate model, and thermodynamic models for the gas state in combustion and exhaust strokes are incorporated to simulate the engine cycle. The gas exchange process, generated work and completeness of combustion are predicted using semi-empirical correlations. The resulting model is parameterized for the combustion of Primary Reference Fuel (PRF) blends using 5703 simulations from a detailed thermo-kinetic model. Semi-empirical correlations in the model are parameterized using the experimental data obtained from a single-cylinder engine.

Because of domestic production from renewable sources and their clean burning nature, alcohols, especially ethanol, have seen growing use as a blending agent and replacement for basic hydrocarbons in gasoline. The increasing use of alcohol in fuels raises questions on the safety of these fuels under certain non-operational situations. Modern vehicles use evaporative emission control systems to minimize environmental emissions of fuel. These systems must be relatively leak-free to function properly and are self-diagnosed by the vehicle On-Board Diagnostic system. When service is required, the service leak testing procedures may involve forcing test gases into the “evap” system and also exposure of the fuel vapors normally contained in the system to atmosphere. Previous work has discussed the hazards involved when performing shop leak testing activities for vehicles fuelled with conventional hydrocarbon gasoline [1, 2].

Although HCCI engines promise low NOx emissions with high efficiency, they suffer from a narrow operating range between knock and misfire because they lack a direct means of controlling combustion timing. A series of previous studies showed that reformer gas, (RG, defined as a mixture of light gases dominated by hydrogen and carbon monoxide), can be used to control combustion timing without changing mixture dilution, (λ or EGR) which control engine load. The effect of RG blending on combustion timing was found to be mainly related to the difference in auto-ignition characteristics between the RG and base fuel. The practical effectiveness of RG depends on local production using a fuel processor that consumes the same base fuel as the engine and efficiently produces high-hydrogen RG as a blending additive.

Homogeneous Charge Compression Ignition (HCCI) combustion offers high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a significant operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved vary with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis during operation, injecting a variable blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism.

Biodiesels are promising alternatives to diesel fuel since they are biodegradable, non-toxic and reduce air pollution. This study presents analytical comparisons of atomization characteristics of 3 types of biodiesels and 6 blends with Diesel No. 2. Results showed that the smallest and largest drop sizes were associated with coconut and peanut biodiesel blends, respectively. Using unblended biodiesels increases drop size by 40%, which indicates either custom nozzles should be used in such applications or blending is required to reduce surface tension and viscosity to enhance atomization. Knowledge of atomization of pure biodiesel and its blends as alternative fuels in diesel engines can lead to better design of diesel engine injectors to meet regulatory emission guidelines and engine performance.

As a first step toward better understanding of the effects of flame stretch on combustion rate in SI engines, the burning velocity of a premixed, spherical, laminar methane-air flame propagating freely at standard temperature and pressure was investigated. The underlying un-stretched burning velocity was computed using CHEMKIN 3.7 with GRI mechanism, while the Lewis number and subsequently the Markstein length were deduced theoretically. The burning velocity of the freely growing flame ball was calculated from the un-stretched burning velocity with curvature and stretch effects accounted via the theoretically deduced Markstein length. For the positive Markstein length methane-air flame, flame stretching reduces the burning velocity. Therefore, the burning velocity of a spark-ignited flame starts with a value lower than, and increases asymptotically to, the underlying un-stretched burning velocity as the flame grows.

It is commonly stated that natural gas-fueled forklifts produce less emissions than propane-fueled forklifts. However, there is relatively little proof. This paper reports on a detailed comparative study at one plant in Edmonton, Canada where a fleet of forklift trucks is used for indoor material movement. (For convenience, the acronym NGV, ie. Natural Gas Vehicle is used to designate natural gas-fueled and LPG, ie. Liquified Petroleum Gas, is used to designate propane-fueled forklifts). Until recently the forklift trucks (of various ages) were LPG carburetted units with two-way catalytic converters. Prompted partially by worker health concerns, the forklifts were converted to fuel injected, closed-loop controlled NGV systems with three-way catalytic converters. The NGV-converted forklifts reduced emissions by 77% (NOX) and 76% (CO) when compared to just-tuned LPG forklifts.

Energy supply and environmental concerns have led to interest in alternative transportation fuels and power-trains. Already, there are significant changes in mainstream gasoline and Diesel formulation to accommodate tighter emissions standards. Some alternative fuels are being promoted as “cleaner” replacements for gasoline and Diesel fuel. There are many research papers which present data on these different alternative fuels, yet it is difficult to compare the fuels with any confidence. The majority of published studies do not use consistent methodology and make many assumptions (which may or may not be reported). Based on an extensive literature review, this study presents emissions results drawn from a smaller number of papers which provide alternative fuel and conventional emissions data in a comparable manner. Both light-duty and heavy-duty vehicles are considered.

This paper presents an investigation of a reverse flow catalytic converter attached to a diesel/natural gas dual fuel engine. Experimental data were obtained in a ceramic monolith catalytic converter with a palladium based catalyst. A variety of flow reversal cycle times were explored experimentally when the engine load was changed from a high load to a low load. A single channel numerical model was developed for the data set and the effect of reverse flow cycle time was studied using both physical and numerical model systems. The duration of the cycle time is shown to be an important parameter in the operation of the converter. Shorter cycle times produced the least fluctuation in reactor temperature and gave the highest time-averaged conversion. Intermediate cycle times gave the most rapid increase in the maximum reactor temperature.

Life Cycle Analysis (LCA) considers the key environmental impacts for the entire life cycle of alternative products or processes in order to select the best alternative. An ideal LCA would be an expensive and time consuming process because any product or process typically involves many interacting systems and a considerable amount of data must be analysed for each system. Practical LCA methods approximate the results of an ideal analysis by setting limited analysis boundaries and by accepting some uncertainty in the data values for the systems considered. However, there is no consensus in the LCA field on the correct method of selecting boundaries or on the treatment of data set uncertainty. This paper demonstrates a new method of selecting system boundaries for LCA studies and presents a brief discussion on applying Monte Carlo Analysis to treat the uncertainty questions in LCA.

Life Cycle Value Assessment (LCVA) is a decision making tool which considers environmental, economic and/or social aspects for the entire life cycle of a product or process from “cradle-to-grave”. LCVA can be used for a wide range of public policy and business decisions with the analysis being performed at various levels of rigour. By its nature, LCVA utilizes data sets of varying qualities drawn from a wide range of sources. The uncertainties in the input data obviously lead to uncertainties in the results of the LCVA analysis. To establish confidence in an LCVA's recommendations, it is important to consider these uncertainties and incorporate an assessment of uncertainty into the LCVA process. However, the diverse nature of the data sets being used makes it difficult to rigorously establish data uncertainty levels. In addition, the complexity of most life cycle models makes it difficult to trace uncertainty through the analysis process.

Fuel choices are being made today by consumers, industry and government. One such choice is whether to use reformulated gasoline to replace regular unleaded gasoline. A second choice involves the source of crude oil, with synthetic crude oil from tar sands currently expanding its share of the Canadian supply. Decision makers usually work with the direct economic consequences of their fuel choice. However, they generally lack the knowledge to measure environmental aspects of different fuel systems. This paper uses Life Cycle Value Assessment (LCVA) to demonstrate how the life cycle environmental aspects can be compared for alternative fuel choices. LCVA is an engineering decision making tool which provides a framework for the decision maker to consider the key economic and environmental impacts for the entire life cycle of alternative products or process systems.

Transportation, with its high energy consumption, is commonly recognized as a major contributor to local, regional, and global environmental impacts. With around 95% of transportation energy originating from petroleum and an increasing emphasis on the associated environmental impacts, alternative transportation fuels are receiving great attention from industry, government, researchers, and the public. When the motivation for developing alternative fuels is to reduce environmental impact, a rigorous tool is needed for comparing the effects of very different alternative and conventional fuels. Such an evaluation tool must consider not only the effects of fuel combustion, but also the effects of producing, refining/processing, distributing, and disposing of wastes associated with that fuel… in other words, the life cycle effects of the fuel.

The effects of turbulence on 60% stoichiometric, premixed methane-air flame propagation were investigated using high speed schlieren video and pressure trace analyses. The mixtures were centrally spark-ignited at 300 K and 101 kPa in a 125 mm cubical chamber. Turbulence was up to 2 m/s intensity with 2 to 8 mm integral scale. With quiescent mixtures, buoyancy convected the slow-burning flame upward onto the upper wall, resulting in dramatic heat loss. With turbulence, the burning rate was enhanced profoundly, though partial flame quenching resulted in cyclic variability at higher turbulence levels. Despite this partial quenching, these ultra-lean flames generally resisted total extinguishment over the conditions tested.

The different roles played by small and large eddies in engine combustion were studied. Experiments compared natural gas combustion in a converted, single cylinder Volvo TD 102 engine and in a 125 mm cubical cell. Turbulence is used to enhance flame growth, ideally giving better efficiency and reduced cyclic variation. Both engine and test cell results showed that flame growth rate correlated best with the level of high frequency, small eddy turbulence. The more effective, small eddy turbulence also tended to lower cyclic variations. Large scales and bulk flows convected the flame relative to cool surfaces and were most important to the initial flame kernel.

Diesel engined buses are the major means of transportation in many urban and suburban areas. Compared with other transportation systems, bus fleets are flexible, effective and low in capital cost. However, existing buses contribute to a serious air pollution problem in many cities. They also consume large amounts of diesel fuel, which is a concern for national economies where locally available natural gas could displace the more expensive petroleum-based fuel. New engine designs significantly reduce pollutants and some use alternative fuels. However, there is a huge infrastructure of existing diesel buses. Expensive new buses or bus engines will only gradually displace them, particularly in countries with weaker economies. The urgently required fuel replacement and pollution reduction benefits must be deferred into the future. These factors lead to the requirement for an economically viable, clean-burning conversion system to convert existing diesel engines to natural gas fuel.

This study describes the design and proof-of-concept testing of a system which has enabled sub-zero cold starting of a port-injected V6 engine fuelled with M100. At -30°C, the engine could reach running speed about 5s after the beginning of cranking. At a given temperature, starts were achieved using a fraction of the mixture enrichment normally required for the more volatile M85 fuels. During cold start cranking, firing is achieved using a high energy plasma jet ignition system. The achievement of stable idling following first fire is made possible through the use of an Exhaust Charged Cycle (ECC) camshaft design. The ECC camshaft promptly recirculates hot exhaust products, unburnt methanol and partial combustion products back into the cylinder to enhance combustion. The combined plasma jet/ECC system demonstrated exceptionally good combustion stability during fast idle following sub-zero cold starts.