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The downsizing of internal combustion engines to increase fuel economy leads to challenges in both obtaining ignition and stabilizing combustion at boosted intake pressures and high exhaust gas recirculation dilution conditions. The use of non-thermal plasma ignition technologies has shown promise as a means to more reliably ignite dilute charge mixtures at high pressures. Despite progress in fundamental research on this topic, both the capabilities and operation implications of emerging non-thermal plasma ignition technologies in internal combustion engine applications are not yet fully explored. In this work, we document the effects of using a corona discharge ignition system in a single cylinder gasoline direct injection research engine relative to using a traditional inductive spark ignition system under conditions associated with both naturally aspirated (8 bar BMEP) and boosted (20 bar BMEP) loads at moderate (2000 rpm) and high (4000 rpm) engine speeds.

Development of SI engines to further increase engine efficiency is strongly affected by the occurrence of engine knock. Engine knock has been widely investigated over the years and the main promoting parameters have been identified as load (temperature and pressure), mixture composition, engine speed, characteristic of the fuel, combustion chamber design, and etc. In this paper a new model for predicting engine knock in 0-D environment is presented. The model is based on the well-known approach of using a Livengood and Wu knock integral. Ignition delay data that are supplied to the knock integral are for specific fuel calculated by detail chemical kinetics and are comprised of low temperature heat release ignition delay and high temperature heat release ignition delay. Next, the cycle to cycle variations of engine and temperature stratification of the end gas have to be taken into account.

The objective of this research is the characterization of ringing in HCCI engines based on in-cylinder ion signal measurements. A correlation is identified to quantify ringing intensity from ion signals by comparing ion and pressure signal characteristics under ringing conditions in an HCCI engine. The maximum ion rise rate (dIon/dtmax) is shown to be an excellent indicator of the maximum pressure rise rate (dP/dtmax), a factor which is very important to measure ringing intensity. The effects of changing bias voltage and ion sensing resistors are also explored for their effects upon the ion ringing intensity. The results show that the ion ringing intensity correlation is accurate at quantifying ringing across a range of HCCI engine operating conditions, including various equivalence ratios, combustion timings and intake pressures.

Ion sensors have been shown to be a low-cost and robust method of measuring start of combustion (SOC) in Homogeneous Charge Compression Ignition (HCCI) engines. The combustion event in an HCCI engine is governed by temperature sensitive chemical-kinetics and is highly fuel dependent. Autoignition variability between various fuels can also affect emissions, efficiency, and overall operating range of the HCCI engine. Ion sensors (i.e. modified spark-plugs) can be used pragmatically to detect the combustion event for various fuels in HCCI engines over a wide range of operating conditions. An investigation of the ion currents produced from the combustion of gasoline, ethanol, and n-heptane in a 1.9L 4-cylinder VW TDI diesel engine (converted to run in HCCI mode) is conducted over a range of equivalence ratios, intake temperatures, and intake pressures. Gasoline, ethanol and n-heptane have diverse autoignition characteristics which affect the overall operation of the HCCI engine.

We numerically simulate a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with a blend of ethanol and diethyl ether by means of a stochastic reactor model (SRM). A 1D CFD code is employed to calculate gas flow through the engine, whilst the SRM accounts for combustion and convective heat transfer. The results of our simulations are compared to experimental measurements obtained using a Caterpillar CAT3401 single-cylinder Diesel engine modified for HCCI operation. We consider emissions of CO, CO2 and unburnt hydrocarbons as functions of the crank angle at 50% heat release. In addition, we establish the dependence of ignition timing, combustion duration, and emissions on the mixture ratio of the two fuel components. Good qualitative agreement is found between our computations and the available experimental data.

The influence of the small amounts (1-3%) of the additive di-tertiary butyl peroxide (DTBP) on the combustion event of Homogeneous Charge Compression Ignition (HCCI) engines was investigated using engine experiments, numerical modeling, and carbon-14 isotope tracing. DTBP was added to neat ethanol and diethyl ether (DEE) in ethanol fuel blends for a range of combustion timings and engine loads. The addition of DTBP to the fuel advanced combustion timing in each instance, with the DEE-in-ethanol mixture advancing more than the ethanol alone. A numerical model reproduced the experimental results. Carbon-14 isotope tracing showed that more ethanol burns to completion in DEE-in-ethanol blends with a DTBP additive when compared to results for DEE-in-ethanol without the additive. However, the addition of DTBP did not elongate the heat release in either case.

We have conducted a detailed numerical analysis of HCCI engine operation at low loads to investigate the sources of HC and CO emissions and the associated combustion inefficiencies. Engine performance and emissions are evaluated as fueling is reduced from typical HCCI conditions, with an equivalence ratio ϕ = 0.26 to very low loads (ϕ = 0.04). Calculations are conducted using a segregated multi-zone methodology and a detailed chemical kinetic mechanism for iso-octane with 859 chemical species. The computational results agree very well with recent experimental results. Pressure traces, heat release rates, burn duration, combustion efficiency and emissions of hydrocarbon, oxygenated hydrocarbon, and carbon monoxide are generally well predicted for the whole range of equivalence ratios. The computational model also shows where the pollutants originate within the combustion chamber, thereby explaining the changes in the HC and CO emissions as a function of equivalence ratio.

Experimental tests were conducted on a Cummins B5.9 direct-injected diesel engine fueled with biodiesel blends. 20% and 50% blend levels were tested, as was 100% (neat) biodiesel. Emissions of particulate matter (PM), nitrogen oxides (NOx), hydrocarbons (HC) and CO were measured under steady-state operating conditions. The effect of biodiesel on total PM emissions was mixed; however, the contribution of the volatile organic fraction to total PM was greater for higher biodiesel blend levels. When only non-volatile PM mass was considered, reductions were observed for the biodiesel blends as well as for neat biodiesel. The biodiesel test fuels increased NOx, while HC and CO emissions were reduced. PM collected on quartz filters during the experimental runs were analyzed for carbon-14 content using accelerator mass spectrometry (AMS).

The contribution of lubrication oil to particulate matter (PM) emissions from a Cummins B5.9 Diesel engine was measured using accelerator mass spectrometry to trace carbon isotope concentrations. The engine operated at fixed medium load (285 N-m (210 ft.lbs.) at 1600 rpm) used 100% biodiesel fuel (B100) with a contemporary carbon-14 (14C) concentration of 103 amol 14C/mg C. The 14C concentration of the exhaust CO2 and PM were 102 and 99 amol 14C/mg C, respectively. The decrease in 14C content in the CO2 and PM are due to the consumption of lubrication oil which is 14C-free. Approximately 4% of the carbon in PM came from lubrication oil under these operating conditions.

A multi-zone model has been developed that accurately predicts HCCI combustion and emissions. The multi-zone methodology is based on the observation that turbulence does not play a direct role on HCCI combustion. Instead, chemical kinetics dominates the process, with hotter zones reacting first, and then colder zones reacting in rapid succession. Here, the multi-zone model has been applied to analyze the effect of piston crevice geometry on HCCI combustion and emissions. Three different pistons of varying crevice size were analyzed. Crevice sizes were 0.26, 1.3 and 2.1 mm, while a constant compression ratio was maintained (17:1). The results show that the multi-zone model can predict pressure traces and heat release rates with good accuracy. Combustion efficiency is also predicted with good accuracy for all cases, with a maximum difference of 5% between experimental and numerical results.

The addition of oxygenates to diesel fuel can reduce particulate emissions, but the underlying chemical pathways for the reductions are not understood. While measurements of particulate matter (PM), unburned hydrocarbons (HC), and carbon monoxide (CO) are routine, determining the contribution of carbon atoms in the original fuel molecules to the formation of these undesired exhaust emissions has proven difficult. Using accelerator mass spectrometry (AMS) diagnostics, carbon atoms in a specific bond position in a specific fuel molecule can be labeled with carbon-14 (14C) and traced through the combustion event to determine whether they reside in PM, HC, CO, CO2, or other emission products. This knowledge of how specific molecular structures produce certain emissions can be used to refine chemical-kinetic combustion models and to optimize fuel composition to reduce undesired emissions.

This research work has focused on measuring the effect of fuel/air mixing on performance and emissions for a homogeneous charge compression ignition engine running on propane. A laser instrument with a high-velocity extractive probe was used to obtain time-resolved measurements of the fuel concentration both at the intake manifold and from the cylinder for different levels of fuel-air mixing. Cylinder pressure and emissions measurements have been performed at these mixing levels. From the cylinder pressure measurements, the IMEP and peak cylinder pressure were found. The fuel-air mixing level was changed by adding the fuel into the intake system at different distances from the intake valve (40 cm and 120 cm away). It was found that at the intake manifold, the fuel and air were better mixed for the 120 cm fuel addition location than for the 40 cm location.

The addition of oxygenates to diesel fuel reduces particulate emissions, but the mechanisms responsible for the reductions are not well understood. Measurement of particulate matter (PM), unburned hydrocarbons (HC), and carbon monoxide (CO) are routine, but determining the origin of the carbon atoms that make up these undesired emissions is difficult. The sub-attomole (<6×105 atoms) sensitivity of accelerator mass spectrometry (AMS) for measuring carbon-14 (14C) allows tracing the carbon atoms from specific fuel components to soot or gaseous emissions. Radioactive materials are not required because contemporary carbon (e.g., ethanol from grain) has 1000 times more 14C than petroleum-derived fuels. The specificity of the 14C tracer and the sensitivity of AMS were exploited to investigate the relative contribution to diesel engine PM, CO, and CO2 from ethanol and diesel fractions of blended fuels.

A summary is presented of experimental results obtained from a Cummins B5.9 175 hp, direct-injected diesel engine fueled with oxygenated diesel blends. The oxygenates tested were dimethoxy methane (DMM), diethyl ether, a blend of monoglyme and diglyme, and ethanol. The experimental results show that particulate matter (PM) reduction is controlled largely by the oxygen content of the blend fuel. For the fuels tested, the effect of chemical structure was observed to be small. Isotopic tracer tests with ethanol blends reveal that carbon from ethanol does contribute to soot formation, but is about 50% less likely to form soot when compared to carbon from the diesel portion of the fuel. Numerical modeling was carried out to investigate the effect of oxygenate addition on soot formation. This effort was conducted using a chemical kinetic mechanism incorporating n-heptane, DMM and ethanol chemistry, along with reactions describing soot formation.

We have developed a methodology for predicting combustion and emissions in a Homogeneous Charge Compression Ignition (HCCI) Engine. The methodology judiciously uses a fluid mechanics code followed by a chemical kinetics code to achieve great reduction in the computational requirements; to a level that can be handled with current computers. In previous papers, our sequential, multi-zone methodology has been applied to HCCI combustion of short-chain hydrocarbons (natural gas and propane). Applying the same procedure to long-chain hydrocarbons (iso-octane) results in unacceptably long computational time. In this paper, we show how the computational time can be made acceptable by developing a segregated solver. This reduces the run time of a ten-zone problem by an order of magnitude and thus makes it much more practical to make combustion studies of long-chain hydrocarbons.

Engine fuel tests were conducted with an oxygenated fuel called Cetaner blended with conventional diesel fuel to determine its emissions reduction potential. Blends of 10, 20, 30 and 40% by volume were investigated. The test engine was a 1993 Cummins B5.9 diesel rated at 175 hp. Emissions of particulate matter (PM), oxides of nitrogen (NOx), hydrocarbons (HC) and carbon monoxide (CO), along with brake specific fuel consumption (bsfc) were measured during steady state operation at eight engine speed-load conditions. Soluble organic fraction (SOF) analysis was also carried out on the collected PM filter samples. The experimental results showed that the Cetaner blends can substantially reduce PM emissions. Reductions were observed in both the organic and inorganic fractions of the collected PM. On a modal-averaged basis, increasing Cetaner blend levels yielded greater PM reductions, with reductions of about 3-4% observed for each 1% of oxygen blended to the fuel by mass.

The numerical and experimental investigation of NOx and soot emission reduction by 3 methods of water addition to a Diesel engine has been presented. Of the 3 methods, 2 add water in air and one adds water in fuel. The Water-in-Air methods are valve port injection of water or spraying water continuously into the turbocharger inlet. Experimentally these two methods of water in air are considered. Numerical investigations of the chemical kinetic aspects of the combustion of n-heptane/water mixture are performed assuming the model of concentric shells of a homogenous reactor. However, a simplified turbulent mixing and detailed chemical kinetics have been considered. Thermo chemical data and the detailed chemical kinetics for each shell are computed by the CHEMKIN package of numerical codes.

Engine fuel tests were conducted with two oxygenates blended with conventional diesel and a synthetic Fisher-Tropsch (F-T) diesel to determine their emissions reduction potential. The oxygenated additives evaluated were dimethoxy methane (DMM) (also known as methylal) and diethyl ether (DEE). Blends of 5, 10, 20 and 30% by volume were investigated. The test engine was a 1993 Cummins B5.9 diesel, and data was collected for steady state operation at nine engine speed-load conditions. Experimental results show that all of the test fuels reduce PM when data is averaged across the nine engine operating modes. The largest reductions in PM were observed with a blend of 30% DMM in diesel, which yielded a 35% reduction compared to the baseline diesel fuel. Lower DMM blend levels also resulted in PM reductions, but to a lesser extent. On a modal averaged basis, F-T diesel reduced PM emissions by 29%, and DEE in concentrations of 10 to 30% reduced PM emissions by between 13 and 24%.

“Gas-to-liquids” catalytic conversion technologies show promise for liberating stranded natural gas reserves and for achieving energy diversity worldwide. Some gas-to-liquids products are used as transportation fuels and as blendstocks for upgrading crude-derived fuels. Methylal (CH3-O-CH2-O-CH3), also known as dimethoxymethane or DMM, is a gas-to-liquid chemical that has been evaluated for use as a diesel fuel component. Methylal contains 42% oxygen by weight and is soluble in diesel fuel. The physical and chemical properties of neat methylal and for blends of methylal in conventional diesel fuel are presented. Methylal was found to be more volatile than diesel fuel, and special precautions for distribution and fuel tank storage are discussed. Steady state engine tests were also performed using an unmodified Cummins B5.9 turbocharged diesel engine to examine the effect of methylal blend concentration on performance and emissions.

Recent studies suggest that the use of ethers as fuels or fuel additives may be a key to the simultaneous reduction of both particulate and NOx emissions from Diesel engines. The present study is directed towards understanding the chemical kinetics of autoignition of ethers under Diesel-like conditions. Autoignition experiments were performed in a constant volume apparatus (CVA), that allowed independent control of temperature, pressure, and oxidizing gas composition. Hollow cone sprays of methanol, dimethyl ether (DME), CH3OCH3, and dimethoxy methane (DMM), CH3OCH2OCH3, were created in quiescent air with a standard Diesel injector, and autoignition delays were inferred from pressure-time histories. A detailed chemical kinetic mechanism was developed to describe the pyrolysis, oxidation, and autoignition of methanol, DME and DMM at high pressures. The mechanism predicts autoignition delay time under Diesel-like conditions.