Compare petrol and diesel engine pdf
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Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. This chapter provides an overview of the various elements that determine fuel consumption in a light-duty vehicle LDV. The primary concern here is with power trains that convert hydrocarbon fuel into mechanical energy using an internal combustion engine and which propel a vehicle though a drive train that may be a combination of a mechanical transmission and electrical machines hybrid propulsion.
A brief overview is given here of spark-ignition SI and compression-ignition CI engines as well as hybrids that combine electric drive with an internal combustion engine; these topics are discussed in detail in Chapters 4 through 6. The amount of fuel consumed depends on the engine, the type of fuel used, and the efficiency with which the output of the engine is transmitted to the wheels.
This fuel energy is used to overcome 1 rolling resistance primarily due to flexing of the tires, 2 aerodynamic drag as the vehicle motion is resisted by air, and 3 inertia and hill-climbing forces that resist vehicle acceleration, as well as engine and drive line losses. Although modeling is discussed in detail in later chapters Chapters 8 and 9 , a simple model to describe tractive energy requirements and vehicle energy losses is given here as well to understand fuel consumption fundamentals.
Also included is a brief discussion of customer expectations, since performance, utility, and comfort as well as fuel consumption are primary objectives in designing a vehicle.
Fuel efficiency is a historical goal of automotive engineering. And indeed, in the s through the s peak efficiencies went from 10 percent to as much as 40 percent, with improvements in fuels, combustion system design, friction reduction, and more precise manufacturing processes. Engines became more powerful, and vehicles became heavier, bigger, and faster.
However, by the late s, fuel economy had become important, leading to the first large wave of foreign imports. The act established the Corporate Average Fuel Economy CAFE program, which required automobile manufacturers to increase the average fuel economy of passenger cars sold in the United States in to a standard of Department of Transportation DOT to set appropriate standards for light trucks.
Before proceeding, it is necessary to define the terms fuel economy and fuel consumption ; these two terms are widely used, but very often interchangeably and incorrectly, which can generate confusion and incorrect interpretations:.
Fuel economy is a measure of how far a vehicle will travel with a gallon of fuel; it is expressed in miles per gallon. This is a popular measure used for a long time by consumers in the United States; it is used also by vehicle manufacturers and regulators, mostly to communicate with the public. As a metric, fuel economy actually measures distance traveled per unit of fuel. Fuel consumption is the inverse of fuel economy.
It is the amount of fuel consumed in driving a given distance. It is measured in the United States in gallons per miles, and in liters per kilometers in Europe and elsewhere throughout the world.
Fuel consumption is a fundamental engineering measure that is directly related to fuel consumed per miles and is useful because it can be employed as a direct measure of volumetric fuel savings.
It is actually fuel consumption. The details of this calculation are shown in Appendix E. Fuel consumption is also the appropriate metric for determining the yearly fuel savings if one goes from a vehicle with a given fuel consumption to one with a lower fuel consumption. Because fuel economy and fuel consumption are reciprocal, each of the two metrics can be computed in a straight-forward manner if the other is known.
This relationship is not linear, as illustrated by Figure 2. Also shown in the figure is the decreasing influence on fuel savings that accompanies increasing the fuel economy of high-mpg vehicles. Each bar represents an increase of fuel economy by percent or the corresponding decrease in fuel consumption by 50 percent. The data on the graph show the resulting decrease in fuel consumption per miles and the total fuel saved in driving 10, miles.
The dramatic decrease in the impact of increasing miles per gallon by percent for a high-mpg vehicle is most visible in the case of increasing the miles per gallon rating from 40 mpg to 80 mpg, where the total fuel saved in driving 10, miles is only gallons, compared to gallons for a change from 10 mpg to 20 mpg. Likewise, it is instructive to compare the same absolute value of fuel economy changes—for example, mpg and mpg.
The mpg fuel saved in driving 10, miles would be 50 gallons, as compared to the gallons in going from mpg. Appendix E discusses further implications of the relationship between fuel consumption and fuel economy for various fuel economy values, and particularly for those greater than 40 mpg.
Figure 2. Figures 2. Because of the nonlinear relationship in Figure 2. Larrick and Soll further conducted three experiments to test whether people reason in a linear but incorrect manner about fuel economy. These experimental studies demonstrated a systemic misunderstanding of fuel economy as a measure of fuel efficiency.
Using linear reasoning about fuel economy leads people to undervalue small improvements mpg in lower-fuel-economy mpg range vehicles where there are large decreases in fuel consumption Larrick and Soll, in this range, as shown in Figure 2. Fischer further discusses the potential benefits of utilizing a metric based on fuel consumption as a means to aid consumers in calculating fuel and cost savings resulting from improved vehicle fuel efficiency.
Throughout this report, fuel consumption is used as the metric owing to its fundamental characteristic and its suitability for judging fuel savings by consumers. In cases where the committee has used fuel economy data from the. The width of each rectangle represents a 50 percent decrease in FC or a percent increase in FE. The number within the rectangle is the decrease in FC per miles, and the number to the right of the rectangle is the total fuel saved over 10, miles by the corresponding 50 percent decrease in FC.
Because of this, the committee recommends that the fuel economy information sticker on new cars and trucks should include fuel consumption data in addition to the fuel economy data so that consumers can be familiar with this fundamental metric since fuel consumption difference between two vehicles relates directly to fuel savings. The fuel consumption metric is also more directly related to overall emissions of carbon dioxide than is the fuel economy metric.
Motor vehicles have been powered by gasoline, diesel, steam, gas turbine, and Stirling engines as well as by electric and hydraulic motors. These internal combustion engines are of two types: gasoline spark-ignition and diesel compression-ignition. The discussion also addresses alternative power trains, including hybrid electrics.
Gasoline engines, which operate on a relatively volatile fuel, also go by the name Otto cycle engines after the person who is credited with building the first working four-stroke internal combustion engine.
Over the years, variations of the conventional operating cycle of gasoline engines have been proposed. A recently popular variation is the Atkinson cycle, which relies on changes in valve timing to improve efficiency at the expense of lower peak power capability. This report uses the generic term compression-ignition engines to refer to diesel engines. The distinction between these two types of engines is changing with the development of engines having some of the characteristics of both the Otto and the diesel cycles.
Although technologies to implement homogeneous charge compression ignition HCCI will most likely not be available until beyond the time horizon of this report, the use of a homogeneous mixture in a diesel cycle confers the characteristic of the Otto cycle. Likewise the present widespread use of direct injection in gasoline engines confers some of the characteristics of the diesel cycle. In a conventional vehicle propelled by an internal combustion engine, either SI or CI, most of the energy in the fuel goes to the exhaust and to the coolant radiator , with about a quarter of the energy doing mechanical work to propel the vehicle.
This is partially due to the fact that both engine types have thermodynamic limitations, but it is also because in a given drive schedule the engine has to provide power over a range of speeds and loads; it rarely operates at its most efficient point.
This is illustrated by Figure 2. It plots the engine efficiency as functions of torque and speed. The plot in Figure 2. In conventional vehicles, however, the engine needs to cover. One way to improve efficiency is to use a smaller engine and to use a turbocharger to increase its power output back to its original level. This reduces friction in both SI and CI engines as well as pumping losses.
Other methods to expand the high-efficiency operating region of the engine, particularly in the lower torque region, are discussed in Chapters 4 and 5. As discussed in Chapter 6 , part of the reason that hybrid electric vehicles show lower fuel consumption is that they permit the internal combustion engine to operate at more efficient speed-load points. The monitoring of engine and emission control parameters by the onboard diagnostic system identifies emission control system malfunctions.
A more recent development in propulsion systems is to add one or two electrical machines and a battery to create a hybrid vehicle. Such vehicles can permit the internal combustion engine to shut down when the vehicle is stopped and allow brake energy to be recovered and stored for later use. Hybrid systems also enable the engine to be downsized and to operate at more efficient operating points. Although there were hybrid vehicles in production in the s, they could not compete with conventional internal combustion engines.
What has changed is the greater need to reduce fuel consumption and the developments in controls, batteries, and electric drives. Hybrids are discussed in Chapter 6 , but it is safe to say that the long-term future of motor vehicle propulsion may likely include advanced combustion engines, combustion engine-electric hybrids, electric plug-in hybrids, hydrogen fuel cell electric hybrids, battery electrics, and more.
The challenge of the next generation of propulsion systems depends not only on the development of the propulsion technology but also on the associated fuel or energy infrastructure.
The large capital investment in manufacturing capacity, the motor vehicle fleet, and the associated fuel infrastructure all constrain the rate of transition to new technologies. The combustion process within internal combustion engines is critical for understanding the performance of SI versus CI engines. SI-engine combustion occurs mainly by turbulent flame propagation, and as turbulence intensity. A more detailed explanation is provided in Chapter 4 of this report.
Thus, combustion characteristics have little effect on the ability of this type of engine to operate successfully at high speeds.
Therefore, this type of engine tends to have high power density e. CI engine combustion is governed largely by means of the processes of spray atomization, vaporization, turbulent diffusion, and molecular diffusion. Therefore, CI combustion, in comparison with SI combustion, is less impacted by engine speed.
As engine speed increases, the combustion interval in the crank-angle domain also increases and thus delays the end of combustion. This late end of combustion delays burnout of the particulates that are the last to form, subjecting these particulates to thermal quenching.
The consequence of this quenching process is that particulate emissions become problematic at engine speeds well below those associated with peak power in SI engines. This ultimately limits the power density i. While power density gets much attention, torque density in many ways is more relevant. Thermal auto ignition in SI engines is the process that limits torque density and fuel efficiency potential. This type of combustion is typically referred to as engine knock, or simply knock.
If this process occurs prior to spark ignition, it is referred to as pre-ignition. This is typically observed at high power settings. Knock and pre-ignition are to be avoided, as they both lead to very high rates of combustion pressure and ultimately to component failure. While approaches such as turbocharging and direct injection of SI engines alter this picture somewhat, the fundamentals remain.
CI diesel engines, however, are not knock limited and have excellent torque characteristics at low engine speed.
That is, at equal engine displacement, the turbocharged diesel tends to deliver superior vehicle launch performance as compared with that of its naturally aspirated SI engine counterpart.
The fuels and the SI and CI engines that use them have co-evolved in the past years in response to improved technology and customer demands. Engine efficiencies have improved due to better fuels, and refineries are able to provide the fuels demanded by modern engines at a lower cost.
Diesel engine , any internal-combustion engine in which air is compressed to a sufficiently high temperature to ignite diesel fuel injected into the cylinder , where combustion and expansion actuate a piston. It converts the chemical energy stored in the fuel into mechanical energy , which can be used to power freight trucks, large tractors, locomotives, and marine vessels. A limited number of automobiles also are diesel-powered, as are some electric-power generator sets. The diesel engine is an intermittent-combustion piston-cylinder device. It operates on either a two-stroke or four-stroke cycle see figure ; however, unlike the spark-ignition gasoline engine , the diesel engine induces only air into the combustion chamber on its intake stroke.
Diesel engine , any internal-combustion engine in which air is compressed to a sufficiently high temperature to ignite diesel fuel injected into the cylinder , where combustion and expansion actuate a piston. It converts the chemical energy stored in the fuel into mechanical energy , which can be used to power freight trucks, large tractors, locomotives, and marine vessels. A limited number of automobiles also are diesel-powered, as are some electric-power generator sets. The diesel engine is an intermittent-combustion piston-cylinder device. It operates on either a two-stroke or four-stroke cycle see figure ; however, unlike the spark-ignition gasoline engine , the diesel engine induces only air into the combustion chamber on its intake stroke. Diesel engines are typically constructed with compression ratios in the range to
A big part of the diesel engine vs petrol engine comparison is the fuel-efficiency figures. Diesels are simply better in this department, as much as.
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The classification of the petrol and diesel engine is done on the basis of the respective fuel used by these engines. The engine which uses petrol is called petrol engine while that uses diesel is called diesel engine. Here will discuss all the major differences among these engines. An internal combustion engine that works on petrol fuel is called petrol engine.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. This chapter provides an overview of the various elements that determine fuel consumption in a light-duty vehicle LDV.
The diesel engine , named after Rudolf Diesel , is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to the mechanical compression; thus, the diesel engine is a so-called compression-ignition engine CI engine. This contrasts with engines using spark plug -ignition of the air-fuel mixture, such as a petrol engine gasoline engine or a gas engine using a gaseous fuel like natural gas or liquefied petroleum gas. Diesel engines work by compressing only the air.
Anyone can learn for free on OpenLearn, but signing-up will give you access to your personal learning profile and record of achievements that you earn while you study. Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available. The vast majority of the world's road vehicles are powered by petrol and diesel internal combustion engines ICEs , so I will start by looking at this technology, the emissions involved and ways that these emissions could be reduced. The petrol-fuelled spark-ignition engine is characterised by the use of a spark plug to initiate the combustion process.
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The primary difference between Petrol and Diesel engines is that the Petrol engine works on the Otto cycle whereas the Diesel engine works on the Diesel cycle.
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