Influence of injection timing on the exhaust emissions of a dual-fuel CI engine

Environmental concerns and limited amount of petroleum fuels have caused interests in the development of alternative fuels for internal combustion (IC) engines. As an alternative, biodegradable, and renewable fuel, ethanol is receiving increasing attention. Therefore, in this study, influence of injection timing on the exhaust emission of a single cylinder, four stroke, direct injection, naturally aspirated diesel engine has been experimentally investigated using ethanol blended diesel fuel from 0% to 15% with an increment of 5%. The engine has an original injection timing 27° CA BTDC. The tests were performed at five different injection timings (21°, 24°, 27°, 30°, and 33° CA BTDC) by changing the thickness of advance shim. The experimental test results showed that NO_x and CO₂ emissions increased as CO and HC emissions decreased with increasing amount of ethanol in the fuel mixture. When compared to the results of original injection timing, at the retarded injection timings (21° and 24° CA BTDC), NO_x and CO₂ emissions increased, and unburned HC and CO emissions decreased for all test conditions. On the other hand, with the advanced injection timings (30° and 33° CA BTDC), HC and CO emissions diminished, and NO_x and CO₂ emissions boosted for all test conditions.     

Performance,emission and combustion characteristics of a DI diesel engine using waste plastic oil

Increase in energy demand, stringent emission norms and depletion of oil resources have led the researchers to find alternative fuels for internal combustion engines. On the other hand waste plastic pose a very serious environment challenge because of their disposal problems all over the world. Plastics have now become indispensable materials in the modern world and application in the industrial field is continually increasing. In this context, waste plastic solid is currently receiving renewed interest. The properties of the oil derived from waste plastics were analyzed and compared with the petroleum products and found that it has properties similar to that of diesel. In the present work, waste plastic oil was used as an alternate fuel in a DI diesel engine without any modification. The present investigation was to study the performance, emission and combustion characteristics of a single cylinder, four-stroke, air-cooled DI diesel engine run with waste plastic oil. The experimental results have showed a stable performance with brake thermal efficiency similar to that of diesel. Carbon dioxide and unburned hydrocarbon were marginally higher than that of the diesel baseline. The toxic gas carbon monoxide emission of waste plastic oil was higher than diesel. Smoke reduced by about 40% to 50% in waste plastic oil at all loads.     

Effect of advanced injection timing on the performance of rapeseed oil in diesel engines

Combustion studies on both diesel fuel and vegetable oil fuels, with the standard and advanced injection timing, were carried out using the same engine and test procedures so that comparative assessments may be made. The diesel engine principle demands self-ignition of the fuel as it is injected at some degrees before top dead centre (BTDC) into the hot compressed cylinder gas. Longer delays between injection and ignition lead to unacceptable rates of pressure rise with the result of diesel knock because too much fuel is ready to take part in premixed combustion. Alternative fuels have been noted to exhibit longer delay periods and slower burning rate especially at low load operating conditions hence resulting in late combustion in the expansion stroke. Advanced injection timing is expected to compensate these effects. The engine has standard injection timing of 30°C BTDC. The injection was first advanced by 5.5°C given injection timing of 35.5°C BTDC. The engine performance was very erratic on this timing. The injection was then advanced by 3.5°C and the effects are presented in this paper. The engine performance was smooth especially at low load levels. The ignition delay was reduced through advanced injection but tended to incur a slight increase in fuel consumption. Moderate advanced injection timing is recommended for low speed operations.     

Effects of preheating of crude palm oil (CPO) on injection system, performance and emission of a diesel engine

Crude palm oil (CPO) is one of the vegetable oils that have potential for use as fuels for diesel engines. CPO is renewable, and is safe and easy to handle. However, at room temperature (30–32°C) CPO has a viscosity about 10 times higher than that of diesel. To lower CPO’s viscosity to the level of diesel’s viscosity, a heating temperature of at least 92 °C is needed. At this temperature, there is a concern that the close-fitting parts of the injection system might be affected. This study focused on finding out the effects of preheating of fuel on the injection system utilising a modified method of friction test, which involves injecting fuel outside the combustion chamber during motoring. Results show that preheating of CPO lowered CPO’s viscosity and provided smooth fuel flow, but did not affect the injection system, even heating up to 100 °C. Nevertheless, heating up to such a high temperature offered no benefits in terms of engine performance. However, heating is necessary for smooth flow and to avoid fuel filter clogging. Both can be achieved by heating CPO to 60 °C. Combustion analyses comparisons between CPO and diesel found that CPO produced a higher peak pressure of 6%, a shorter ignition delay of 2.6°, a lower maximum heat release rate and a longer combustion period. Over the entire load range, CPO combustion produced average CO and NO emissions that were 9.2 and 29.3% higher, respectively, compared with those from diesel combustion.     

Effect of advanced injection timing on emission characteristics of diesel engine running on natural gas

There has been a growing concern on the emission of greenhouse gases into the atmosphere, whose consequence is global warming. The sources of greenhouse gases have been identified, of which the major contributor is the combustion of fossil fuel. Researchers have intensified efforts towards identifying greener alternative fuel substitutes for the present fossil fuel. Natural gas is now being investigated as potential alternative fuel for diesel engines. Natural gas appears more attractive due to its high octane number and perhaps, due to its environmental friendly nature. The test results showed that alternative fuels exhibit longer ignition delay, with slow burning rates. Longer delays will lead to unacceptable rates of pressure rise with the result of diesel knock. This work examines the effect of advanced injection timing on the emission characteristics of dual-fuel engine. The engine has standard injection timing of 30° BTDC. The injection was first advanced by 5.5° and given injection timing of 35.5° BTDC. The engine performance was erratic on this timing. The injection was then advanced by 3.5°. The engine performance was smooth on this timing especially at low loading conditions. The ignition delay was reduced through advanced injection timing but tended to incur a slight increase in fuel consumption. The CO and CO₂ emissions were reduced through advanced injection timing.     

Effect of fuel opening injection pressure and injection timing of hydrogen enriched rice bran biodiesel fuelled in CI engine

Fuel opening injection pressure and injection timing are important injection parameters, and they have a significant influence on engine combustion, performance, and emissions. The focus of this work is to improve the performance and emissions of single-cylinder diesel engines by using injection parameters in engines running with rice bran biodiesel 10% blend (RB10+H₂) and 20% blend (RB20+H₂) with a fixed hydrogen flow rate of 7 lpm. In addition, hydrogen and biodiesel are excellent alternatives to conventional fuels, which can reduce energy consumption and strict emission standards. The investigation is conducted for three different opening injection pressure of 220, 240, 260 bar, and four different injection timings of 20°, 22°, 24°, and 26° bTDC. Results indicate that the sample ‘RB10+H₂’ provides 3.32% higher BTE and reduces the fuel consumption by 13% as diesel fuel. The blend RB10+H₂ attributes a maximum cylinder pressure of 68.7 bar and a peak HRR value of 49 J/ºCA. Further, compared to diesel, RB10+H₂ blend emits lower CO, HC, and smoke opacity by 17%, 22%, and 16%, respectively. However, an almost 12% increase of nitrogen oxides for the RB10+H₂ blend is observed. However, with advanced injection timing and higher opening injection pressure, NOx emissions is slightly increased.     

Characterisation and effect of using waste plastic oil and diesel fuel blends in compression ignition engine

Plastics have now become indispensable materials in the modern world and application in the industrial field is continually increasing. The properties of the oil derived from waste plastics were analyzed and found that it has properties similar to that of diesel. Waste plastic oil (WPO) was tested as a fuel in a D.I. diesel engine and its performance characteristics were analysed and compared with diesel fuel (DF) operation. It is observed that the engine could operate with 100% waste plastic oil and can be used as fuel in diesel engines. Oxides of nitrogen (NO_x) was higher by about 25% and carbon monoxide (CO) increased by 5% for waste plastic oil operation compared to diesel fuel (DF) operation. Hydrocarbon was higher by about 15%. Smoke increased by 40% at full load with waste plastic oil compared to DF. Engine fueled with waste plastic oil exhibits higher thermal efficiency upto 80% of the full load and the exhaust gas temperature was higher at all loads compared to DF operation.     

Direct injection of hydrogen main fuel and diesel pilot fuel in a retrofitted single-cylinder compression ignition engine

Up to 90% hydrogen energy fraction was achieved in a hydrogen diesel dual-fuel direct injection (H2DDI) light-duty single-cylinder compression ignition engine. An automotive-size inline single-cylinder diesel engine was modified to install an additional hydrogen direct injector. The engine was operated at a constant speed of 2000 revolutions per minute and fixed combustion phasing of ?10 crank angle degrees before top dead centre (°CA bTDC) while evaluating the power output, efficiency, combustion and engine-out emissions. A parametric study was conducted at an intermediate load with 20–90% hydrogen energy fraction and 180-0 °CA bTDC injection timing. High indicated mean effective pressure (IMEP) of up to 943 kPa and 57.2% indicated efficiency was achieved at 90% hydrogen energy fraction, at the expense of NO_x emissions. The hydrogen injection timing directly controls the mixture condition and combustion mode. Early hydrogen injection timings exhibited premixed combustion behaviour while late injection timings produced mixing-controlled combustion, with an intermediate point reached at 40 °CA bTDC hydrogen injection timing. At 90% hydrogen energy fraction, the earlier injection timing leads to higher IMEP/efficiency but the NO_x increase is inevitable due to enhanced premixed combustion. To keep the NO_x increase minimal and achieve the same combustion phasing of a diesel baseline, the 40 °CA bTDC hydrogen injection timing shows the best performance at which 85.9% CO₂ reduction and 13.3% IMEP/efficiency increase are achieved.     

Experimental investigations on the effect of fuel injection parameters on diesel engine fuelled with biodiesel blend in diesel with hydrogen enrichment

Fuel injection pressure and injection timing are two extensive injection parameters that affect engine performance, combustion, and emissions. This study aims to improve the performance, combustion, and emissions characteristics of a diesel engine by using karanja biodiesel with a flow rate of 10 L per minute (lpm) of enriched hydrogen. In addition, the research mainly focused on the use of biodiesel with hydrogen as an alternative to diesel fuel, which is in rapidly declining demand. The experiments were carried out at a constant speed of 1500 rpm on a single-cylinder, four-stroke, direct injection diesel engine. The experiments are carried out with variable fuel injection pressure of 220, 240, and 260 bar, and injection timings of 21, 23, and 25 °CA before top dead center (bTDC). Results show that karanja biodiesel with enriched hydrogen (KB20H10) increases BTE by 4% than diesel fuel at 240 bar injection pressure and 23° CA bTDC injection timing. For blend KB20H10, the emissions of UHC, CO, and smoke opacity are 33%, 16%, and 28.7% lower than for diesel. On the other hand NOx emissions, rises by 10.3%. The optimal injection parameters for blend KB20H10 were found to be 240 bar injection pressure and 23 °CA bTDC injection timing based on the significant improvement in performance, combustion, and reduction in exhaust emissions.     

Optimization of diesel engine input parameters running on Polanga biodiesel to improve performance and exhaust emission using MOORA technique with standard deviation

Fast exhausting fossil fuel reserves and high rise in the air pollution levels due to combustion of these fuels bound us to discover some cleaner and environment-friendly fuels for the engines. Biodiesel from edible and non-edible seed oils has been identified as a better alternate of the diesel fuel in engines with a little sacrifice in terms of power output but with an improvement in exhaust emissions. The aim of the present research work is to optimize the input parameters of diesel engine running on Polanga biodiesel to improve performance and exhaust emissions. The input parameters selected for optimization are fuel injection timing, fuel injection pressure, Polanga biodiesel blend, and engine load with respect to brake thermal efficiency, brake specific fuel consumption, hydrocarbon emission, smoke opacity, and emission of nitrogen oxides. Relative weights of the response variables were calculated by standard deviation. The optimum combination of input parameters was obtained by Taguchi-based Multi-Objective Optimization by Ratio Analysis. Experiments were performed according to Taguchi’s L₁₆ orthogonal array in a random manner in which three replicates of each experiment were noted. The optimum combination of input parameters for maximum performance and minimum exhaust emissions found to be as fuel injection timing 27° bTDC, fuel injection pressure –? 220 bar, biodiesel blend –? B40, and engine load –? 60%. The optimum values of the response variables, at the obtained optimum combination of input parameters, were predicted by Taguchi method and then verified experimentally and a good relation was found between them. These optimum values found to be as brake thermal efficiency –? 36.351%, brake specific fuel consumption –? 0.322 kg/kW-h, hydrocarbon emission –? 2.193 ppm, smoke opacity –? 80.925 HSU, and NO_x emission –? 690.987 ppmv.     

Oxides of nitrogen emissions from biodiesel-fuelled diesel engines

Biodiesel has received, and continues to receive, considerable attention for its potential use as an augmenting fuel to petroleum diesel. Its advantages include decreased net carbon dioxide, hydrocarbon, carbon monoxide, and particulate matter emissions, and fuel properties similar to petroleum diesel for ease of use in diesel engines. Its disadvantages include poorer cold flow characteristics, lower heating values, and mostly reported higher emissions of oxides of nitrogen (NO_x = NO + NO₂, where NO is nitric oxide and NO₂ is nitrogen dioxide). This latter disadvantage (i.e., higher emissions of oxides of nitrogen) is the focus of this review article. NO_x formation mechanisms are complex and affected by several different features (e.g., size, operating points, combustion chamber design, fuel system design, and air system design) of internal combustion engines. The slight differences in properties between biodiesel and petroleum diesel fuels are enough to create several changes to system and combustion behaviors of diesel engines. Combined, these effects lead to several complex and interacting mechanisms that make it difficult to fundamentally identify how biodiesel affects NO_x emissions. Instead, it is perhaps better to say that several parameters seem to most strongly influence observed differences in NO_x emissions with biodiesel, thus introducing several possibilities for inconsistency in the trends. These parameters are injection timing, adiabatic flame temperature, radiation heat transfer, and ignition delay. This article provides a review of the rich literature describing these parameters, and provides additional insight into the system responses that are manifested by the use of biodiesel.     

Tertiary recycling of waste plastic using catalytic cracking into crude oil

Disposal of waste plastic and excessive use of fossil fuels have caused environmental problems in the world. According to an estimate, more than 100 million tonnes plastics are produced every year and after their usage these plastics are discarded to become waste. Both plastic- and petroleum-derived fuels are hydrocarbons that contain the elements of carbon and hydrogen. The main difference between these hydrocarbons is that plastic molecules have longer carbon chains than those of LPG, petrol and diesel fuels. Therefore, it is possible to convert waste plastic into fuels. Pyrolysis is a prospective method to handle waste plastics. The purpose of this study is to explore the ability of different types of catalysts in conversion of plastic waste to low-emissive hydrocarbon fuel. Pyrolysis experiments were conducted using three different catalysts to check their ability in increasing the production. Catalytic degradation with potato peels yielded 74.52 wt% liquid fuel product. So far, the use of potato peels as a biocatalyst in pyrolysis process has not been reported. The pyrolysis oil was analyzed by GC/MS to determine its elemental composition. The liquid products obtained were compatible with international standards. Therefore, two main global problems such as problem of waste plastic management and problem of shortage of fuel are being tackled together.     

Energy,exergy and emission analysis on a DI single cylinder diesel engine using pyrolytic waste plastic oil diesel blend

Depletion of fossil fuels and stringent emission norms focus attention to discover an evitable source of alternative fuel in order to attribute a significant compensation on conventional fuels. Besides, waste management policies encourage the valorization of different wastes for the production of alternative fuels in order to reduce the challenges of waste management. In this context, pyrolysis has become an emerging trend to convert different wastes into alternate fuel and suitable to be used as a substitute fuel for CI engines. The current investigation provides a sustainable and feasible solution for waste plastic management by widening the gap between global plastic production and plastic waste generation. It investigates the performance and emission of a single cylinder DI four stroke diesel engine using waste plastic oil (WPO) derived from pyrolysis of waste plastics using Zeolite-A as catalyst. Engine load tests have been conducted taking waste plastic oil and subsequently a blend of waste plastic oil by 10%, 20%, and 30% in volume proportions with diesel as fuel. The performance of the test engine in terms of brake thermal efficiency is found marginally higher and brake specific fuel consumption comparatively lowest for 20% WPO-diesel blend than pure diesel. The NOx and HC emission is found lower under low load condition and became higher by increasing the load as compared to diesel. Fuel exergy was significantly increasing after blending of WPO with pure diesel, but exergetic efficiency of the blended fuels followed the reverse trend. However, increase in load of the engine improved the exergetic efficiency. The 20% WPO–diesel blended fuel is found suitable to be used as an alternative fuel for diesel engine.     

Experimental investigations of a four-stroke single cylinder direct injection diesel engine operated on dual fuel mode with producer gas as inducted fuel and Honge oil and its methyl ester (HOME) as injected fuels

In order to meet the energy requirements, there has been growing interest in alternative fuels like biodiesels, methyl alcohol, ethyl alcohol, biogas, hydrogen and producer gas to provide a suitable diesel oil substitute for internal combustion engines. Vegetable oils present a very promising alternative to diesel oil since they are renewable and have similar properties. Vegetable oils offer almost the same power output with slightly lower thermal efficiency when used in diesel engine [Srivastava A, Prasad R. Triglycerides-based diesel fuels. Renew Sustain Energy Rev 2000;4:111–33. [1]; Vellguth G. Performance of vegetable oils and their monoesters as fuels for diesel engines. SAE 831358, 1983. [2]; Demirbas A. Biodiesel production from vegetable oils via catalytic and non-catalytic supercritical methanol transesterification methods. Int J Prog Energy Combust Sci 2005;31:466–87. [3]; Jajoo BN, Keoti RS. Evaluation of vegetable oils as supplementary fuels for diesel engines. In: Proceedings of the XV national conference on IC engines and combustion, Anna University Chennai, 1997. [4]; Altin R, Cetinkaya S, Yucesu HS. The potential of using vegetable oil fuels as fuel for diesel engines. Int J Energy Convers Manage 2000;42:529–38, 248. [5]; Gajendra Babu MK, Chandan Kumar Das LM. Experimental investigations on a Karanja oil methyl ester fuelled DI diesel engine. SAE 2006-01-0238, 2006. [6]; Agarwal D, Kumar Agarwal A. Performance and emission characteristics of a Jatropha oil (preheated and blends) in a direct injection compression ignition engine. Int J Appl Therm Eng 2007;27:2314–23. [7]]. Research in this direction with edible oils have yielded encouraging results, but their use as fuel for diesel engine has limited applications due to higher domestic requirement [Scholl Kyle W, Sorenson Spencer C. Combustion Analysis of soyabean oil methyl ester in a direct injection diesel engine. SAE 930934, 1993. [8]; Nwafor OMI. Effect of advanced injection timing on the performance of rapeseed oil in diesel engines. Int J Renew Energy 2000;21:433–44. [9]; Nwafor OMI. The effect of elevated fuel inlet temperature on performance of diesel engine running on neat vegetable oil at constant speed conditions. Renew Energy 2003;28:171–81. [10]]. In view of this, Honge oil (Pongamia Pinnata Linn) being non-edible oil could be regarded as an alternative fuel for CI engine applications. The viscosity of Honge oil is reduced by transesterification process to obtain Honge oil methyl ester (HOME).Gasification is a process in which solid biomass is converted into a mixture of combustible gases, which complete their combustion in an IC engine. Hence, producer gas can act as a promising alternative fuel, especially for diesel engines by substituting considerable amount of diesel fuels. Downdraft moving bed gasifiers coupled with IC engine are a good choice for moderate quantities of available biomass, up to 500 kW of electric power. Hence, bioderived gas and vegetable liquids appear more attractive in view of their friendly environmental nature. Since vegetable oils produce higher smoke emissions, dual fuel operation could be adopted for improving their performance.     

Effect of metal based additive on performance emission and combustion characteristics of diesel engine fuelled with biodiesel

This study investigates the use of ferric chloride (FeCl₃) as a fuel borne catalyst (FBC) for waste cooking palm oil based biodiesel. The metal based additive was added to biodiesel at a dosage of 20 μmol/L. Experiments were conducted to study the effect of ferric chloride added to biodiesel on performance, emission and combustion characteristics of a direct injection diesel engine operated at a constant speed of 1500 rpm at different operating conditions. The results revealed that the FBC added biodiesel resulted in a decreased brake specific fuel consumption (BSFC) of 8.6% while the brake thermal efficiency increased by 6.3%. FBC added biodiesel showed lower nitric oxide (NO) emission and slightly higher carbon dioxide (CO₂) emission as compared to diesel. Carbon monoxide (CO), total hydrocarbon (THC) and smoke emission of FBC added biodiesel decreased by 52.6%, 26.6% and 6.9% respectively compared to biodiesel without FBC at an optimum operating condition of 280 bar injection pressure and 25.5^o bTDC injection timing. Higher cylinder gas pressure, heat release rate and shorter ignition delay period were observed with FBC added biodiesel at these conditions.     

Analysis of combustion characteristics,engine performance and exhaust emissions of diesel engine fueled with upgraded waste source fuel

Utilization of the waste products as an alternative fuel could reduce the dependence on fossil fuel. The three types of upgraded waste source fuels discussed in this paper were tire derived fuel (TDF), waste plastic disposal fuel (WPD) and upgraded waste cooking oil (UWCO). The detailed combustion pressure showed that kinematic viscosity and cetane number played an important role in determining the combustion quality. TDF's high kinematic viscosity and low cetane number affected its fuel vaporization process; thus, lengthening its ignition delay. UWCO showed the 14% higher power and 13.8% higher torque compared to diesel fuel (DF). WPD produced the lowest NOx due to its low pressure curve during combustion. TDF had produced the highest exhaust emissions (CO, CO₂, NO and NOx). Particulate matter (PM) emissions by UWCO blends were lower than DF. UWCO's soot concentration was 40% lower than DF and increased to 62.5% from low to high engine speed operation.     

Investigations on the performance and exhaust emissions of a diesel engine using preheated waste frying oil as fuel

In the present experimental investigation, waste frying oil a non-edible vegetable oil was used as an alternative fuel for diesel engine. The high viscosity of the waste frying oil was reduced by preheating. The properties of waste frying oil such as viscosity, density, calorific value and flash point were determined. The effect of temperature on the viscosity of waste frying oil was evaluated. It was determined that the waste frying oil requires a heating temperature of 135 °C to bring down its viscosity to that of diesel at 30 °C. The performance and exhaust emissions of a single cylinder diesel engine was evaluated using diesel, waste frying oil (without preheating) and waste frying oil preheated to two different inlet temperatures (75 and 135 °C). The engine performance was improved and the CO and smoke emissions were reduced using preheated waste frying oil. It was concluded from the results of the experimental investigation that the waste frying oil preheated to 135 °C could be used as a diesel fuel substitute for short-term engine operation.     

The effects of injection timing on NOx emissions of a low heat rejection indirect diesel injection engine

Higher NO_x is one of the major problems to be overcomed in a low heat rejection (LHR) diesel engine as insulation leads to an increase in combustion temperature about 200–250 °C compared to an identical standard (STD) diesel engine. High combustion temperatures alter optimum injection timing of a LHR engine. With the proper adjustment of the injection timing, it is possible to partially offset the adverse effect of insulation on heat release rate and hence to obtain improved performance and lower NO_x. However, the injection timing and brake specific fuel consumption (BSFC) trade-off must be considered together in performance and NO_x emission point of view. In this study, optimum injection timing was found with 4 crank angle (34° CA) retarded before top dead centre (BTDC) in LHR diesel engine in comparison to that of STD diesel engine (38° CA BTDC). When the LHR engine was operated with the injection timing of the 38 crank angle, which is the optimum value of the STD engine, it was shown that NO_x emission increased about 15%. However, when the injection timing was retarded to 34° CA in the LHR case, it was observed a decrease on the NO_x emissions with about 40% and the brake specific fuel consumption (BSFC) with about 6% compared to that of the STD case. Thus, by retarding the injection timing, an additional 1.5% saving in fuel consumption was obtained.     

Science review of internal combustion engines

Internal combustion engines used in transportation produce about 23% of the UK's carbon dioxide emission, up from 14% in 1980. The current science described in this paper suggests that there could be 6–15% improvements in internal combustion fuel efficiency in the coming decade, although filters to meet emission legislation reduce these gains. Using these engines as hybrids with electric motors produces a reduction in energy requirements in the order of 21–28%. Developments beyond the next decade are likely to be dominated by four topics: emission legislation and emission control, new fuels, improved combustion and a range of advanced concepts for energy saving. Emission control is important because current methods for limiting nitrogen oxides and particulate emissions imply extra energy consumption. Of the new fuels, non-conventional fossil-derived fuels are associated with larger greenhouse gas emissions than conventional petroleum-based fuels, while a vehicle propelled by fuel cells consuming non-renewable hydrogen does not necessarily offer an improvement in emissions over the best hybrid internal combustion engines. Improved combustion may be developed for both gasoline and diesel fuels and promises better efficiency as well as lower noxious emissions without the need for filtering. Finally, four advanced concepts are considered: new thermodynamic cycles, a Rankine bottoming cycle, electric turbo-compounding and the use of thermoelectric devices. The latter three all have the common theme of trying to extract energy from waste heat, which represents about 30% of the energy input to an internal combustion engine.