Newsletter No 34

12 June 2006

 

 

 Hi Folks

 

I last wrote to you a month ago.

Not because I am lazy or on holiday or having become a politician.

No ! We have been very busy at Nick’s Racing.

 

Before you swear at my throwing a whole bunch of Dyno graphs at you, let me explain.

All of a sudden it came to be known that I could reduce the fuel consumption of most vehicles considerably. This is done by Careful jetting on Carburetted motors (see the first Graph of a 2.4L Hilux). A UNICHIP will do similar on an EFI motor, if new (3.3 Nissan in the 2’nd graph) or old (3L Nissan in the last graph).

On Efi motors we can also adjust the Timing all over the range, giving you those flatter curves.

All of this is not voodoo, it is enhancing a vehicles efficiency.

 

For those of you more technically minded, the following Article explains it best.

 

You CAN be too Rich
By Klaus Allmendinger, VP of Engineering, Innovate Motorsports

Many people with turbochargers believe that they need to run at very rich mixtures. The theory is that the excess fuel cools the intake charge and therefore reduces the probability of knock. It does work in reducing knock, but not because of charge cooling. The following little article shows why.

First let’s look at the science. Specific heat is the amount of energy required to raise 1 kg of material by one degree K (Kelvin, same as Celsius but with 0 point at absolute zero). Different materials have different specific heats. The energy is measured in kJ or kilojoules:

Air ~ 1 kJ/( kg * deg K)
Gasoline 2.02 kJ/( kg * deg K)
Water 4.18 kJ/( kg * deg K)
Ethanol 2.43 kJ/( kg * deg K)
Methanol 2.51 kJ/( kg * deg K)

Fuel and other liquids also have what's called latent heat. This is the heat energy required to vaporize 1 kg of the liquid. The fuel in an internal combustion engine has to be vaporized and mixed thoroughly with the incoming air to produce power. Liquid gasoline does not burn. The energy to vaporize the fuel comes partially from the incoming air, cooling it. The latent heat energy required is actually much larger than the specific heat. That the energy comes from the incoming air can be easily seen on older carbureted cars, where frost can actually form on the intake manifold from the cooling of the charge.

The latent heat values of different liquids are shown here:

Gasoline 350 kJ/kg
Water 2256 kJ/kg
Ethanol 904 kJ/kg
Methanol 1109 kJ/kg
Most engines produce maximum power (with optimized ignition timing) at an air-fuel-ratio between 12 and 13. Let's assume the optimum is in the middle at 12.5. This means that for every kg of air, 0.08 kg of fuel is mixed in and vaporized. The vaporization of the fuel extracts 28 kJ of energy from the air charge. If the mixture has an air-fuel-ratio of 11 instead, the vaporization extracts 31.8 kJ instead. A difference of 3.8 kJ. Because air has a specific heat of about 1 kJ/kg*deg K, the air charge is only 3.8 C (or K) degrees cooler for the rich mixture compared to the optimum power mixture. This small difference has very little effect on knock or power output.

If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can't burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.

So where does the knock suppression of richer mixtures come from?

If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.

So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power.

Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard.

Optimum mix with “later” ignition can produce more power because more energy is released from the combustion of gasoline. Here’s why: When hydrocarbons like gasoline combust, the burn process actually happens in multiple stages. First the gasoline molecules are broken up into hydrogen and carbon. The hydrogen combines with oxygen from the air to form H2O (water) and the carbon molecules form CO. This process happens very fast at the front edge of the flame front. The second stage converts CO to CO2. This process is relatively slow and requires water molecules (from the first stage) for completion. If there is no more oxygen available (most of it consumed in the first stage), the second stage can't happen. But about 2/3 of the energy released from the burning of the carbon is released in the second stage. Therefore a richer mixture releases less energy, lowering peak pressures and temperatures, and produces less power. A secondary side effect is of course also a lowering of knock probability. It's like closing the throttle a little. A typical engine does not knock when running on part throttle because less energy and therefore lower pressures and temperatures are in the cylinder.

This is why running overly-rich mixtures can not only increase fuel consumption, but also cost power.

This is all fine and well at Wide Open Throttle. But since most cars tend to cruise at below ˝ throttle I would rather look at running a very lean mixture with lots of advance.

In the picture next door we did nothing else except remove the stock restrictive Airfilter. You might argue that the removal of that restriction causes the Power increase up to 10 Kw on a ford V6 and more on a Carburetted 4500 Cruiser. The Article above shows it is not that simple. Also the Curve is at WOT, but I can tell you that Power will increase all over. Careful examination of the Curve shows you there is a power drop of at Low RPM that we can rectify by judicious adjustments.

Adding a K&N will give you more Power still due to the still air it produces.

 

All I am trying to say that whatever you change around your Engine management will produce a change in Power and more importantly power characteristics. So before you rip out that rear silencer think ! What effect will it have on your gasflow and burn rate/characteristic ?

That is why we do development on certain vehicles trying to find what gives the customer the most Bang for his buck.

 

Talking about Developments on the new Toyota VVTi bakkies:

4L        K&N followed by the tuned header exhaust system and then a UNICHIP

2.7       UNICHIP gives you a healthy increase in overall power, especially if coupled to the tuned header exhaust system. We only test fitted a K&N yesterday and gave the manufacturing go-ahead. Delivery time 2 months..

 

As you can see it is not always the same order. For instance the Exhaust system on the 2.7 for N$ 3500 makes less relative performance increase than the UNICHIP for N$ 2500. But on the 4L the Exhaust + K&N for a tad over 5 Grand is far better value for money than the UNICHIP for 2500.

My outlook in life is not how cheap something is, but rather how can I spend what little money I have, with the most effect.

 

Next week my Exhaust systems, headers etc. will increase substantially. You may still order now, quoting this Newsletter # 34.

 

Anybody heard anything about the New TATA bakkies (Telcoline Single cab 4X4) ?

A good friend wants to buy one for farming use.

Same person is looking for a 12 Volt Freezer holding about 80 L.

 

That’s it for now

Nick

Remember that Mechanical Engineers build weapons.  Civil Engineers build targets.

The Optimist says: "The glass is half full"
The Pessimist says: "The glass is half empty"
The Engineer says: "The glass is twice the size it should be"