Join Date: May 2014
Award Points: 10
| | The Concept Behind Mileage
IMP:please don't merge this thread anywhere,
BECAUSE THIS THREAD IS NOT ABOUT GETTING MORE FE.,ITS ABOUT UNDERSTANDING THE CONCEPT BEHIND IT.
ITS A UNIQUE THREAD.
FOR PRO USERS!!
The Ideal law.
All engines in IDEAL condition must cover a same unit distance for unit of fuel
Ie: energy produced=work done(conditions apply)
1)car must already be running in its average speed
2) you are driving in vaccum(no wind ressistance)
3)all moving parts are 100% lubricated
4)no variation in throttle
5)same O2 level in intake
6)no wear in parts
7)air filter is not present (must be breathing 100% pure air)
8)all energy produced is converted as distance.
9)no load variation
10)same gear ratio (only one gear, taller one, because car is already running in its average speed)
So these conditions are not practically possible
Main reasons why all cars differ in its fuel efficiency figures
• They have different engine sizes
• They have different parts amd shapes,(ac compressor,alternator,passenger,tyre size,weight,wind ressistance……… etc.)
• They have different gear ratios and acceleration graphs
• They have different air intake and injector levels
Things you need to understand before getting max fuel efficiency
There is only 20% error due to vehicle, rest is from us driving the vehicle.
So there are infinite factors affecting cars mileage??? Lets brake down to few important factors,
Cars have different torque and power band at varying rpm, also they have different gear ratios, so what you need to do is drive in higher gear as possible without loading your engine,
Every engines job is to take air and fuel into cylinders and make rotational energy converted to tyres,where more pressure in fuel will cause less pickup in higher speeds,at taller gears in low speeds.
So let engine do its job, so don’t hit on accelerator and expect car to have amazing acceleration, you need efficiency rather than speed.
Say if you are in a signal, say 50s left, first thing you need to do is switch of engine, if you think car will suck fuel if u start engine over again then you are wrong, it only consumes 10s of idling fuel, so if signal time is 10s, you don’t need to switch of engines.
Now signal is open and what you do??
Switch to first and move?? Yes, but not longer ,all cars have shorter first gears ,so switching to second gear within seconds is useful to gain 2.3% of fuel
Now don’t rev more!! Only limit your revs to 30%-50%, depending on your need,
In second and third gear be soft in throttle, many mistakes in feather throttling and not throttling at all,All you need to do is linearly accelerate to your max efficiency speed level, and maintain your momentum, cars have a specific rpm to get max fuel efficiency, but common thing is its not over 30% of rpm,cars have specific rpm levels with each gears for max fuel efficiency,Also you need to consider that limiting revs,is not the factor, you need to keep the momentum of car,now you are in the efficient momentum, then all you need to do is maintain those momentum,linear throttling, helps save up to 25% of fuel efficiency.
Say if your car has efficient RPM of 2000rpm, then let’s assume these factors,
1st = 10kmph
So you are attaining different speeds in different gears with same amount of fuel used!!!
Now you understand the concept??? Covering more distance for same amount of fuel,These things are the main factors reducing fuel efficiency,so you need to do is travel in higher gear as possible
Going fast is so tempting. Not only do we do it to keep up with the flow of traffic, but if we can save even five minutes, it seems worth it. But if you're on the highway, driving 100 kmph per hour instead of 120 kmph will save you 2-4 kms per liter over the duration of your trip.
Windows up. Again, this is tough, especially on pleasant days. But having the windows down creates aerodynamic drag that causes an engine to work harder. On the highway, this can decrease fuel economy by up to 10 percent.
Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by 33% at highway speeds and by 5% around town.1 Sensible driving is also safer for you and others, so you may save more than gas money.
Avoid keeping unnecessary items in your vehicle, especially heavy ones. An extra 100 pounds in your vehicle could reduce your MPG by up to 2%. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones.
Idling can use a half liter of fuel per hour, depending on engine size and air conditioner (AC) use. Turn off your engine when your vehicle is parked. It only takes a few seconds worth of fuel to restart your vehicle. Turning your engine on and off excessively, however, may increase starter wear.
Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.
When you use overdrive gearing, your car's engine speed goes down. This saves gas and reduces engine wear.
• If cars piston seals are worn out will extremely reduce economy, also will burn engine oil with fuel and will destroy engine soon
• Tighten up the cam drive belt, so all valve timings and ignition timing will work in a flow to maximise efficiency
• Worn out clutch plate, will drastically reduce FE,so change if any issues are there.
• Check compression pressure in cylinder for any leak in gaskets and piston rings
• Do a dyno test ,to make sure you are with stocks performance curves
road load power = av + bv² + cv³
The letter ‘v’ represents the velocity of the car, and the letters a, b and crepresent three different constants:
The ‘a’ component comes mostly from the rolling resistance of the tires, and friction in the car's components, like drag from the brake pads, or friction in the wheel bearings.
The’ b ‘component also comes from friction in components, and from the rolling resistance in the tires. But it also comes from the power used by the various pumps in the car.
The’ c’ component comes mostly from things that affect aerodynamic drag like the frontal area, drag coefficient and density of the air.
These constants will be different for every car. But the bottom line is, if you double your speed, this equation says that you will increase the power required by much more than double. A hypothetical medium sized SUV that requires 20 horsepower at 50 mph might require 100 horsepower at 100 mph
Efficiency of an Engine
In effect the efficiency of the engine is improving. It uses a fixed amount of fuel to power itself and the accessories, and a variable amount of fuel depending on the power required to keep the car going at a given speed. So in terms of fuel used per mile, the faster the car goes, the better use we make of that fixed amount of fuel required.
This trend continues to a point. Eventually, that road load curve catches up with us. Once the speed gets up into the 40 mph range each 1 mph increase in speed represents a significant increase in power required. Eventually, the power required increases more than the efficiency of the engine improves. At this point the mileage starts dropping. Let's plug some speeds into our equation and see how a 1 mph increase from 2 to 3 mph compares with a 1 mph increase from 50 to 51 mph. To make things easy we'll assume a, b and c are all equal to 1.
Speed Equation Result
3 mph 3+3²+3³ 39
2 mph 2+2²+2³ 14
Power Increase 25
51 mph 51+51²+51³ 135,303
50 mph 50+50²+50³ 127,550
Power Increase 7,753
You can see that the increase in power required to go from 80 to 85 kmph is much greater than to go from 4 to 6 kmph.
So, for most cars, the "sweet spot" on the speedometer is in the range of 80-85 kmph. Cars with a higher road load will reach the sweet spot at a lower speed. Some of the main factors that determine the road load of the car are:
• Coefficient of drag. This is an indicator of how aerodynamic a car is due only to its shape. The most aerodynamic cars today have a drag coefficient that is about half that of some pickups and SUVs.
• Frontal area. This depends mostly on the size of the car. Big SUVs have more than double the frontal area of some small cars.
• Weight. This affects the amount of drag the tires put on the car. Big SUVs can weigh two to three times what the smallest cars weigh.
In general, smaller, lighter, more aerodynamic cars will get their best mileage at higher speeds. Bigger, heavier, less aerodynamic vehicles will get their best mileage at lower speeds.
If you drive your car in the "sweet spot" you will get the best possible mileage for that car. If you go faster or slower, the mileage will get worse, but the closer you drive to the sweet spot the better mileage you will get.
• ACCELERATE LESS
• BRAKE AHEAD
• KEEP STEADY SPEEDS
• CHECK TYRE PRESSURE,AND AIR FILTER
• CLOSE WINDOWS
• DRIVE IN ECONOMY SPEEDS ALWAYS
• KEEP YOUR CAR IN GOOD CONDITION
• KEEP UNWANTED WEIGHTS OUT OF CAR
• KEEP STOCK TYRE SIZE TO REDUCE ROLLING RESISTANCE
• USE OBD ADAPTER FOR ASSISTED DRIVING
Happy miles a head!!!
Make sure to fasten your seat belts!
PLAY SAFE !!,USE SEAT BELTS(SAVED MY LIFE)
PLAY SAFE !!,USE SEAT BELTS(SAVED MY LIFE)